A method for producing a furan derivative containing 5-hydroxymethylfurfural (5-HMF), a furan derivative, a solution containing the furan derivative, and a method for producing a franzicarboxylic acid or franzicarboxylic acid ester.

Abstract

The objective is to provide a method for producing 5-hydroxymethylfurfural from glucose in high yield, with high selectivity, and at low cost. [Solution] The problem is solved by a method for producing 5-hydroxymethylfurfural, which includes the step of contacting glucose with an isomerization catalyst and a dehydration catalyst in a two-phase solvent system of water and an organic solvent that is immiscible with water.

Description

[Technical Field]

[0001] The present invention relates to a method for producing 5-hydroxymethylfurfural (hereinafter also referred to as 5-HMF) by contacting glucose with a mixed catalyst, which is a mixture of an isomerization catalyst and a dehydration catalyst, in a two-phase solvent system of an organic solvent that is immiscible with water and water. Furthermore, the present invention relates to a method for producing formylfuran acetal, which is an intermediate in the production of dicarboxylic acid esters or dicarboxylic acids having a furan skeleton derived from biomass raw materials, and to formylfuran acetal and a solution containing said acetal. The present invention also relates to a method for producing furan derivatives, which are intermediates in the production of franciocarboxylic acid or franciocarboxylic acid esters derived from biomass raw materials, as well as the furan derivatives and solutions containing the furan derivatives. Furthermore, the present invention relates to a method for producing frangic acid or frangic acid ester derived from biomass raw materials. [Background technology]

[0002] In recent years, there has been a growing need to address global environmental issues such as the depletion of fossil fuels and the increase in carbon dioxide in the atmosphere. In response to these societal demands, the development of processes for producing fuels and various useful chemicals from biomass raw materials grown in the current atmospheric environment has attracted attention and is being actively pursued. Methods utilizing biomass raw materials like these are expected to be a viable alternative to petroleum-based raw materials. For example, plant-based raw material production can be dispersed and diversified across various locations, resulting in a highly stable raw material supply. Furthermore, because fuel production and consumption occur within the atmosphere without the consumption of fossil fuels, the material balance between carbon dioxide absorption and emission is relatively balanced. Therefore, it has the potential to realize a circular economy, something that cannot be expected at all with fossil fuels, and thus possesses extremely great industrial value.

[0003] In a series of catalytic reactions that convert biomass raw materials into starting materials for fuels and chemical raw materials, 5-hydroxymethylfurfural (5-HMF) is an important intermediate. 5-HMF is generally produced by intramolecular dehydration of fructose, which has a hexose skeleton, using an acid catalyst. 5-HMF is a raw material for 2,5-dimethylfuran (DMF) and 2,5-franzicarboxylic acid (FDCA). DMF has recently attracted attention as a biofuel to replace fossil fuels, and FDCA is produced as polyethylene furanoate (PEF) by condensation polymerization with ethylene glycol as a substitute for terephthalic acid, which makes up polyethylene terephthalate.

[0004] Patent Document 1 discloses a method for producing 5-HMF from hexoses. Specifically, at 150°C, glucose is heated in a two-phase solvent system of water and a polar organic solvent (methyl isobutyl ketone (MIBK) / 2-BuOH) using poly(styrenesulfonic a 5-HMF is obtained by contacting and reacting with a water-soluble complex catalyst, cid)AlCl3(PSSA-AlCl3). The conversion rate and yield of this method are 95% and 45%, respectively. On the other hand, Non-Patent Document 1 describes a method for obtaining 5-HMF by dissolving fructose in a solvent of N-methylpyrrolidone:water = 70:30, and then passing it through a flow-through reactor packed with a cation ion exchange resin (DIAION RCP160M) catalyst. The conversion rate and yield of this method are 91%. Here, fructose is usually produced by isomerizing glucose. Non-Patent Document 2 describes the isomerization of glucose using glucose isomerase. The isomerization method is described. Since this isomerization reaction is an equilibrium reaction, the yield obtained by this method is 57%. The fructose that is commercially available is produced by separating and recovering fructose that has been generated from glucose to a concentration of slightly over 50%. Non-patent document 3 describes a method for obtaining 5-HMF by contacting glucose with sodium chloride and a cation exchange resin (DIAION RCP160M) catalyst in a two-phase solvent system of water, N-methylpyrrolidone, and methyl isobutyl ketone. The yield of this method is stated to be 84%, and the selectivity is 90%.

[0005] On the other hand, among the series of catalytic reactions that derive useful chemicals from biomass raw materials, processes involving compounds with a furan ring have been proposed as particularly important processes in terms of their functionality, versatility of applications, environmental impact, and economic efficiency. For example, the following reaction method has been proposed for producing franciocarboxylic acid and its esters, which are the target products of the present invention. [ka]

[0006] Regarding specific manufacturing methods, for example, Patent Document 2 proposes a method for producing hydroxymethylfurfural (HMF) from monosaccharides such as glucose and fructose in the presence of hydrated niobic acid, and Patent Documents 3 and 4 propose a method for producing frangic acid (FDCA) or its esters by the oxidation reaction of HMF. However, in the methods for producing frangic acid or its esters by the direct oxidation reaction of HMF described in Patent Documents 3 and 4, HMF has low thermal stability because it has reactive functional groups such as aldehyde groups and hydroxyl groups, and side reactions such as polymerization and ring-opening reactions occur concurrently. These side reactions not only reduce the reaction yield due to the formation of oligomers such as humins, polymers, and levulinic acid, but also cause problems such as reduced thermal conductivity and blockage of the reactor and pipes due to the adhesion of oligomers and polymers to the inside of the reactor and pipes, making stable long-term operation difficult. These problems are particularly pronounced when producing frangic acid or its esters under high HMF concentration conditions, and therefore pose a major challenge in industrial processes where production under low HMF concentration conditions is required and economic efficiency is essential.

[0007] On the one hand, as a highly productive process capable of efficiently producing furandicarboxylic acid (FDCA) or its ester even under high HMF concentration conditions, a method for producing furandicarboxylic acid (FDCA) or its ester using a cyclic acetal of HMF as an intermediate has been proposed in Patent Document 5. However, even in this production method, there remains a problem that when the concentration of the cyclic acetal of HMF is increased, the yield of FDCA decreases. This is because in the production method described in Patent Document 5, the oxidation reaction of the acetal group of the cyclic acetal hardly occurs. In order to promote the oxidation reaction of the acetal group, it is necessary to increase the amount of catalyst used or to conduct the reaction under high-pressure conditions using a high-oxygen-concentration gas. The reaction under such severe oxidation conditions requires the use of high-pressure equipment using a high-oxygen-concentration gas, which increases the construction cost of the production equipment. In addition, since a part of the diol required to obtain the cyclic acetal of HMF is oxidized and consumed, there is a problem that the production cost increases. Further, in order to avoid contamination of the product of this diol decomposition product and the recovered diol, a complicated purification process is required, which further increases the production cost.

Chemical formula

Prior art documents

Patent documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-patent documents

[0009] [Non-Patent Document 1] Chemical Engineering & Processing,Process Intensification,138,2019,65-72 [Non-Patent Document 2] Yoshiyuki Takasaki, "Development of Isomerized Sugars Using Glucose Isomerase," Organic Synthesis Chemistry, 1980, Vol. 38, No. 6, pp. 538-545. [Non-Patent Document 3] Royal Society of Chemistry Advances,2020,10,9492-9498 [Overview of the project] [Problems that the invention aims to solve]

[0010] As described in Non-Patent Document 1, a method for producing 5-HMF from fructose in good yield has been reported. However, this method requires a step of isomerizing glucose to fructose. For example, if fructose is obtained from glucose using the method described in Non-Patent Document 2, and then 5-HMF is produced using the method described in Non-Patent Document 1, the cumulative yield remains at just over 50%.

[0011] When 5-HMF is produced from glucose using the method described in Patent Document 1, the yield is approximately 45%. Furthermore, when 5-HMF is produced from glucose using the method described in Non-Patent Document 3, the yield is improved. However, side reactions form condensates and oligomers such as humic acid, as well as degradation products such as formic acid and levulinic acid, resulting in a low selectivity of 5-HMF, around 90%. These by-products and degradation products may also cause discoloration. If discoloration occurs, complex purification processes such as adsorption decolorization are required to remove the discoloration, leading to increased manufacturing costs. Furthermore, if these by-products and decomposition products adhere to the inside of the reactor, it can lead to a decrease in the reactor's heat transfer efficiency and blockages in the piping, making stable long-term operation difficult.

[0012] In the method described in Non-Patent Document 3, when producing 5-HMF from glucose, the following is used The sodium chloride used leads to the deactivation (capping) of the acidic groups of the cation ion exchange resin, resulting in a shortened catalyst lifespan. Furthermore, it accelerates reactor corrosion, necessitating reactors made of more corrosion-resistant materials, such as glass-lined reactors or Hastelloy reactors. In other words, the method described in Non-Patent Document 3 has the problem of significantly increasing the construction costs of the reaction facility.

[0013] Thus, when producing 5-HMF directly from glucose, the reaction yield and selectivity are still insufficient, and many challenges remain regarding productivity and long-term stable operation. In contrast, the present invention aims to provide a method for producing 5-HMF from glucose in high yield, with high selectivity, and at low cost. More specifically, in the process of producing 5-HMF from glucose, the basic configuration is a process in which a mixed catalyst, which is a mixture of an isomerization catalyst and a dehydration catalyst, is brought into contact with glucose in a two-phase solvent system of an organic solvent that is immiscible with water and water, thereby (1) isomerizing glucose to fructose with the isomerization catalyst, while the partially produced fructose is rapidly and selectively converted to 5-HMF by the dehydration catalyst, and (2) in a two-phase solvent system of an organic solvent that separates in two phases with water and water, the 5-HMF produced during the reaction is distributed into the organic solvent phase as it occurs, so as not to cause decomposition reactions such as the formation of by-products such as formic acid and levulinic acid, or polymerization reactions such as huminization and oligomerization that cause discoloration (the above is the first problem).

[0014] Furthermore, although methods for producing FDCA or its esters by the oxidation reaction of HMF have been proposed in Patent Documents 3 to 5, challenges remain in terms of productivity and manufacturing costs from an industrial perspective. The present invention aims to solve the above-mentioned problems in a method for producing FDCA or its ester by the oxidation reaction of HMF, and to provide a novel intermediate that can be used in a method for producing FDCA or its ester under reaction conditions that are more advantageous in terms of production cost and in high yield (the above is the second problem). [Means for solving the problem]

[0015] The inventors of the present invention have diligently investigated the first problem described above and have found that by reacting a mixed catalyst of an isomerization catalyst and a dehydration catalyst with glucose, and then distributing the resulting 5-HMF into an organic solvent that separates water into two phases (hereinafter also referred to as an organic solvent), side reactions such as the above-mentioned decomposition reaction and polymerization reaction can be prevented, and 5-HMF can be produced in high yield and with high selectivity (94-95%). In other words, the first gist of this invention is as follows:

[0016] [1] A method for producing 5-hydroxymethylfurfural, comprising the step of contacting glucose with a mixed catalyst, which is a mixture of an isomerization catalyst and a dehydration catalyst, in a two-phase solvent system of an organic solvent that is immiscible with water and water. [2] A method for producing 5-hydroxymethylfurfural, comprising a contact step of contacting glucose with an isomerization catalyst and a dehydration catalyst in a two-phase solvent system of water and an organic solvent that is immiscible with water, A method for producing 5-hydroxymethylfurfural, characterized in that the two-phase solvent contains 80 parts by mass or less of an alkali metal salt or an alkaline earth metal salt per 100 parts by mass of glucose. [3] The method for producing 5-hydroxymethylfurfural according to [1] or [2], characterized in that the isomerization catalyst is a metal oxide. [4] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [3], characterized in that the dehydration catalyst is a solid acid. [5] The specific surface area of ​​the isomerization catalyst is 100 m² 2 / g or more, and the specific surface area of ​​the dehydration catalyst is 4 0m 2 A method for producing 5-hydroxymethylfurfural according to any one of [1] to [4], characterized in that the amount is 1 / g or more. [6] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [5], characterized in that the ratio of the product of the specific surface area and the amount of catalyst of the isomerization catalyst to the product of the specific surface area and the amount of catalyst of the dehydration catalyst is 1:20 to 20:1. [7] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [6], characterized in that the mixing ratio (mass ratio) of the isomerization catalyst and the dehydration catalyst is 1:3 to 3:1. [8] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [7], characterized in that the isomerization catalyst is aluminum oxide and the dehydration catalyst is an ion exchange resin. [9] The method for producing 5-hydroxymethylfurfural according to any one of [1] to [8], characterized in that the organic solvent is hydrophobic and is one or more selected from the group consisting of ethers, ketones, aromatic hydrocarbons and saturated aliphatic hydrocarbons.

[10] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [9], characterized in that the boiling point of the organic solvent at atmospheric pressure is 70°C or higher.

[11] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[10] , characterized in that the organic solvent has an inorganic value / organic value ratio of 0.10 or more and 1.00 or less.

[12] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[11] , characterized in that the organic solvent is one or more selected from the group consisting of methyltetrahydropyran (MTHP), methyl isobutyl ketone (MIBK), and methyl ethyl ketone (MEK).

[13] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[12] , characterized in that the mass ratio of the organic solvent to water is 1:1 to 4:1.

[14] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[13] , characterized in that the temperature in the reaction is 120°C or higher.

[0017] <ii>[1] A method for producing 5-hydroxymethylfurfural, comprising the steps of: reacting glucose with a mixed catalyst, which is a mixture of an isomerization catalyst and a dehydration catalyst, in a two-phase solvent system of an organic solvent that is immiscible with water and water; and separating the reaction solution obtained by the reaction into an organic solvent phase containing 5-hydroxymethylfurfural produced by the reaction and an aqueous phase containing sugar and the mixed catalyst contained in the solution after the reaction. [2] A method for producing 5-hydroxymethylfurfural, comprising a contact step of contacting glucose with an isomerization catalyst and a dehydration catalyst in a two-phase solvent system of water and an organic solvent that is immiscible with water, and an oil-water separation step of separating the reaction solution obtained from the reaction into an organic solvent phase containing 5-hydroxymethylfurfural produced by the reaction and an aqueous phase containing sugar and the mixed catalyst contained in the solution after the reaction, A method for producing 5-hydroxymethylfurfural, characterized in that the two-phase solvent contains 80 parts by mass or less of an alkali metal salt or an alkaline earth metal salt per 100 parts by mass of glucose. [3] A method for producing 5-hydroxymethylfurfural according to [1] or [2], characterized in that the isomerization catalyst is a metal oxide and the dehydration catalyst is a solid acid. [4] The specific surface area of ​​the isomerization catalyst is 100 m² 2 / g or more, and the specific surface area of ​​the dehydration catalyst is 40 m² 2 A method for producing 5-hydroxymethylfurfural according to any one of [1] to [3], characterized in that the amount is 1 / g or more. [5] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [4], characterized in that the ratio of the product of the specific surface area and the amount of catalyst of the isomerization catalyst to the product of the specific surface area and the amount of catalyst of the dehydration catalyst is 1:20 to 20:1. [6] The mixing ratio (mass ratio) of the isomerization catalyst and the dehydration catalyst is 1:3 to 3:1. A method for producing 5-hydroxymethylfurfural according to any one of [1] to [5], characterized by the above. [7] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [6], characterized in that the isomerization catalyst is aluminum oxide and the dehydration catalyst is an ion exchange resin. [8] The method for producing 5-hydroxymethylfurfural according to any one of [1] to [7], characterized in that the organic solvent is hydrophobic and is one or more selected from the group consisting of ethers, ketones, aromatic hydrocarbons and saturated aliphatic hydrocarbons. [9] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [8], characterized in that the boiling point of the organic solvent at atmospheric pressure is 70°C or higher.

[10] The method for producing 5-hydroxymethylfurfural according to any one of [1] to [9], characterized in that the organic solvent has an inorganic value / organic value ratio of 0.10 to 1.00.

[11] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[10] , characterized in that the organic solvent is one or more selected from the group consisting of methyltetrahydropyran (MTHP), methyl isobutyl ketone (MIBK), and methyl ethyl ketone (MEK).

[12] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[11] , comprising the step of dissolving (distributing) the 5-hydroxymethylfurfural produced by the above reaction into an organic solvent phase obtained by the oil-water separation step and recovering it.

[13] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[12] , comprising the step of recovering the sugar contained in the solution after the reaction and the mixed catalyst together with the aqueous phase obtained by the oil-water separation step.

[14] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[13] , characterized in that the mass ratio of the organic solvent to water is 1:1 to 4:1.

[15] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[14] , characterized in that the temperature in the reaction is 120°C or higher.

[0018] Furthermore, the inventors diligently investigated the second problem described above and discovered a new method for producing an intermediate that can be used in the production of FDCA or its ester, thereby completing the present invention. They also discovered that the above problem can be solved by using a method that includes specific production steps, thus completing the present invention. By using the intermediate and specific steps according to the present invention, not only FDCA or its ester, but also diformylfuran and formylfurancarboxylic acid having asymmetric substituents can be produced in high yield and with high selectivity.

[0019] In other words, the present invention has the following as its second main feature. <iii>[1] A production method of a furan derivative having an acetal group and a carbonyl group, including an oxidation step of contacting hydroxymethylfurfural acetal with an oxidation catalyst. [2] The production method according to [1], wherein the furan derivative is a compound represented by formula (1). [Chemical formula] (In formula (1), Z is a hydrogen atom or a hydroxyl group, and R 2 and R 3 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent.) [3] The production method according to [1] or [2], wherein in the product after the oxidation step, the concentration of the furan derivative in all the compounds having a furan skeleton is 70 mol% or more. [4] The production method according to any one of [1] to [3], wherein the oxidation catalyst is a metal catalyst. [5] A furan derivative represented by formula (1). [Chemical formula] (In formula (1), Z is a hydrogen atom or a hydroxyl group, and R 2 and R 3 are independently selected from a hydrogen atom, an alkyl group having 1 to​​​​​​​​​​​​​​​(These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.)

[0020] <iv>[1] A method for producing a furan derivative, comprising a deprotection step of synthesizing a furan derivative by deprotecting a formylfuran acetal or an ester thereof, A method for producing the furan derivative, wherein the furan derivative is one or more selected from the group consisting of formylfuranic acid and its esters. [2] The method for producing the compound represented by formula (3) according to [1], wherein the formylfuran acetal or ester thereof is a compound represented by formula (3). [ka] (In formula (3), X, R 4 and R 5 (These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.) [3] In the product after the deprotection step, formyl is present in all compounds having a furan skeleton. The method for producing furanic acid and its esters according to [1] or [2], wherein the concentration of furanic acid and its esters is 70 mol% or more. [4] A manufacturing method according to any one of [1] to [3], further comprising a recovery step of recovering a diol from the reaction solution after the deprotection step. [5] The manufacturing method according to [4], wherein the diol is a diol having 2 to 10 carbon atoms. [6] A solution containing compounds having a furan skeleton, wherein the concentration of formylfuran carboxylic acid and its esters in the total compounds having a furan skeleton is 70 mol% or more.

[0021] <v>[1] A method for producing a furan carboxylic acid or an ester thereof, comprising an oxidation step of contacting a composition containing a furan derivative with an oxidation catalyst, The furan derivative is one or more selected from the group consisting of diformylfuran, formylfuran carboxylic acid, and its esters. A method for producing the furan derivative, wherein the concentration of the furan derivative in the total compounds having a furan skeleton contained in the composition containing the furan derivative is 70% by mass or more. [2] The manufacturing method according to [1], wherein the oxidation catalyst is a metal catalyst. [3] The manufacturing method according to [1] or [2], wherein the reaction temperature in the oxidation step is 50°C or lower.

[0022] <vi>[1] A method for producing frangic acid or frangic acid ester from hydroxymethylfurfural, comprising the following manufacturing steps (i) to (iv). (i) An acetalization step to synthesize hydroxymethylfurfural acetal by acetalizing hydroxymethylfurfural. (ii) A first oxidation step of oxidizing hydroxymethylfurfural acetal to synthesize formylfuran acetal or its ester. (iii) A deprotection step of synthesizing formylfuranic acid or an ester thereof by deprotecting formylfuranic acid acetal or an ester thereof. (iv) A second oxidation step of oxidizing formylfuranic acid or its ester. [2] The method for producing a frangic acid or frangic acid ester according to [1], wherein the formylfuran acetal or ester thereof is a compound represented by formula (3). [ka] (In formula (1), X, R 4 and R 5 (These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.) [3] A method for producing a frangic acid or frangic acid ester according to [1] or [2], wherein in step (i), an organic solvent selected from toluene and methyltetrahydropyran is used. [4] A method for producing a frangic acid or frangic acid ester according to any one of [1] to [3], further comprising a recovery step of recovering a diol from the reaction solution after step (iii). [5] The method for producing a frangic acid or frangic acid ester according to [4], wherein the diol is a diol having 2 to 10 carbon atoms. [Effects of the Invention]

[0023] According to the first gist of the present invention, glucose can be contacted with a mixed catalyst comprising an isomerization catalyst and a dehydration catalyst to isomerize glucose to fructose, while the partially produced fructose can be rapidly and selectively converted to 5-HMF by the dehydration catalyst. Furthermore, by rapidly distributing the produced 5-HMF into an organic solvent, product degradation is prevented, making it possible to produce 5-HMF from glucose at a lower cost with higher yield and selectivity than conventional methods. In other words, this method eliminates the need for a preliminary preparation step to produce a fructose intermediate from the glucose raw material, allowing for the direct production of 5-HMF from the glucose raw material with high yield and selectivity. This reduces the construction costs of manufacturing facilities and avoids complex operational management.

[0024] Furthermore, according to the second aspect of the present invention, a novel intermediate can be provided that can be used in a method for producing FDCA or its ester by the oxidation reaction of HMF. In addition, by using this intermediate, it is possible to lower the reaction pressure and temperature during the oxidation reaction, and the use of high-pressure equipment using high-oxygen concentration gas becomes unnecessary, contributing to a reduction in manufacturing costs. Moreover, it becomes possible to produce FDCA or its ester in high yield. [Modes for carrying out the invention]

[0025] The following describes typical embodiments for carrying out the present invention, but the present invention is not limited to these embodiments unless it exceeds the gist of the invention. Furthermore, in this specification, when "~" is used to express a value with a numerical value or physical property value enclosed before or after it, it shall be used to include the values ​​before and after it.

[0026] <First summary> One embodiment of the present invention (first summary) is a method for producing 5-hydroxymethylfurfural, comprising a contact step of contacting glucose with an isomerization catalyst and a dehydration catalyst in a two-phase solvent system of water and an organic solvent that is immiscible with water.

[0027] <Reaction method> The reaction method according to this embodiment can be implemented in a batch method, in which the substrate, solvent, and catalyst are introduced into the reactor, or in a flow method, in which the solution is circulated through a reactor (such as a fluidized bed or fixed bed) containing the catalyst. The CSTR continuous stirred tank reaction method is also suitably used. The wetted material of the reactor and flow channels is not particularly limited, but examples include glass, stainless steel (SUS), iron, and other metals. Glass or stainless steel (SUS) is preferred because it has corrosion resistance and high energy transfer efficiency. Furthermore, from the viewpoint of manufacturing equipment cost, stainless steel (SUS) is preferred.

[0028] <Organic solvents> The organic solvent used in this embodiment is not particularly limited as long as it is hydrophobic and immiscible with water, and may be a mixture. In other words, it is sufficient if it separates into two phases when mixed with water. The boiling point of the organic solvent used in this embodiment at atmospheric pressure is not particularly limited. It is usually 70°C or higher, preferably 75°C or higher, and more preferably 80°C or higher. On the other hand, the upper limit is usually 250°C or lower, preferably 200°C or lower, and more preferably 150°C or lower. By using an organic solvent within this range, the reaction conversion rate can be improved. Furthermore, the load during the distillation and purification of the recovered organic solvent can be reduced.

[0029] The organic solvent used in this embodiment is not particularly limited. For example, tetrahydropyran, methyltetrahydropyran, dipropyl ether, diisopropyl ether, methyl-t Ethers with 4 to 20 carbon atoms, such as ert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether; 2-butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptone Ketones with 4 to 20 carbon atoms, such as tanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, 3-dodecanone, 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, acetophenone, etc.; acetate Esters such as propyl acetate, butyl acetate, etc.; 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 1-heptanol, 2-heptanol, 1-octanol, 2-octanol, 3-octanol, 2-ethyl-1-hexanol, 1-nonanol, 1-decano Monoalcohols with 4 to 20 carbon atoms, such as 1-undecyl alcohol, 1-lauryl alcohol, 1-tridecyl alcohol, 1-tetradecanol, 1-pentadecanol, 1-hexadecanol, cis-9-hexadecene-1-ol, 1-heptadecanol, 1-octadecanol, 16-methylheptadecene-1-ol, nonadecyl alcohol, arachidyl alcohol, etc.; saturated aliphatic hydrocarbons with 3 to 12 carbon atoms, such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, dodecane, isododecane;Examples include aromatic hydrocarbons such as toluene, xylene, trimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene; lactones such as γ-butyrolactone and γ-valerolactone; and halogenated hydrocarbons such as dichloromethane, chloroform, dichloroethane, tetrachloroethane, and hexachloroethane.

[0030] Among these, it is preferable that the organic solvent is one or more selected from the group consisting of ethers, ketones, esters, lactones, aromatic hydrocarbons, halogenated hydrocarbons, and saturated aliphatic hydrocarbons. More preferably, one or more selected from the group consisting of ethers, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons are selected, and even more preferably, ethers or ketones are particularly preferred.

[0031] As for the ether, cyclic ethers are more preferred. Specifically, examples of cyclic ethers include methyltetrahydropyran (MTHP) and tetrahydropyran (THP). Among these, methyltetrahydropyran (MTHP) is even more preferred because it has a high boiling point at atmospheric pressure, improves the reaction conversion rate in a short time, and provides high reaction selectivity.

[0032] As ketones, methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), and diethyl ketone are more preferred. Methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK) are even more preferred because they have high boiling points at atmospheric pressure, improve the reaction conversion rate in a short time, and provide high reaction selectivity.

[0033] As aromatic compounds, xylene, toluene, and benzene are more preferred. Toluene is even more preferred because it has a high boiling point at atmospheric pressure, improves the reaction conversion rate in a short time, and provides high reaction selectivity. These organic solvents may be used individually or in any ratio and combination of two or more.

[0034] In this embodiment, using the above-mentioned organic solvent having the above-mentioned boiling point improves the reaction conversion rate in a short time and allows 5-HMF to be obtained with high reaction selectivity. Furthermore, since the generated 5-HMF can be efficiently extracted, the recovery rate of 5-HMF by subsequent oil-water separation can be increased.

[0035] The book "Organic Conceptual Theory" ("Systematic Qualitative Analysis of Organic Compounds," by Atsushi Fujita, Kazama Shobo (1974)) proposes inorganic and organic values ​​for solvents. This method calculates organic and inorganic values ​​based on predetermined numerical values ​​for the functional groups constituting organic compounds, and characterizes the properties of organic compounds based on their ratio. In this embodiment, the organic solvent preferably has an inorganic value / organic value ratio defined in "Systematic Organic Qualitative Analysis" by Atsushi Fujita, Kazama Shobo (1974) of 0.10 or more and 1.00 or less. The lower limit is more preferably 0.20 or more, and the upper limit is more preferably 0.90 or less. By selecting a solvent within this range, affinity for not only hydrocarbon groups but also hydroxyl groups and aldehyde groups is increased, making it possible to efficiently extract 5-HMF. Table 1 below shows the inorganic value (I), organic value (O), and their ratio (I / O) for major organic solvents.

[0036] [Table 1]

[0037] The above organic solvent is mixed with water and used in the reaction as a two-phase solvent system. Examples of the two-phase solvent system of an immiscible organic solvent and water in this embodiment include solvents in which water and an organic solvent form two layers, solvents in which the organic solvent is dispersed in an aqueous solvent, and solvents in which water is dispersed in an organic solvent. Furthermore, in the present invention, the solvent consists of a combination of water and an organic solvent that is immiscible with water. A two-phase solvent system is one preferred embodiment because it reduces the load during solvent recovery. The mass ratio of the organic solvent to water is not particularly limited, but is usually 1:1 to 4:1, preferably 2:1 to 4:1. This range is preferable because it allows for efficient extraction of 5-HMF from the aqueous phase and reduces the degradation of 5-HMF. The above mass ratios are those observed under atmospheric pressure and at 25°C.

[0038] <Isomerization catalyst> The isomerization catalyst used in this embodiment is a catalyst that isomerizes glucose to fructose. The isomerization catalyst is preferably a metal oxide, and examples include metal oxides and metal composite oxides such as aluminum oxide, magnesium oxide, calcium oxide, zirconium oxide, aluminum oxide, magnesium oxide, magnesium oxide, calcium oxide, zirconium oxide, aluminum oxide, magnesium oxide, magnesium oxide, calcium oxide, zirconium oxide, and other metal oxides and metal composite oxides, as well as immobilized catalysts such as clay. Among these, aluminum oxide, magnesium oxide, calcium oxide, and zirconium oxide are preferred, and aluminum oxide is particularly preferred. These isomerization catalysts may be used individually or in any ratio and combination of two or more types.

[0039] When aluminum oxide is used as an isomerization catalyst, the specific surface area of ​​the aluminum oxide is preferably 100 m². 2 It is 150m or more / g, more preferably 150m 2 It is 1 / g or more. There is no particular upper limit, but it is usually 500m 2 It is less than or equal to / g, preferably 300m 2 The value is less than or equal to / g. Within this range, the probability of glucose and aluminum oxide coming into contact becomes sufficient, and the isomerization rate can be increased. The specific surface area of ​​aluminum can be measured by the permeation method or the gas adsorption method. Note that the specific surface area value will be the same regardless of which method is used.

[0040] <Dehydration catalyst> The dehydration catalyst used in this embodiment catalyzes the intramolecular dehydration reaction of glucose and fructose. A solid acid is preferred as the dehydration catalyst. A solid acid is a solid that chemically adsorbs a base and either donates a proton to a reactant or accepts an electron pair from a reactant. Preferably, the solid acid is a solid at 25°C and exhibits acidity. Specifically, heteropoly acids, diatomaceous earth phosphate, activated carbon, steam-activated carbon, phosphate-activated carbon, acid-modified silica gel, acid-modified silica alumina, zeolite, ion exchange resin, sulfated ZrO 2 Examples include sulfuric acid-immobilized catalysts and phosphoric acid-immobilized catalysts such as titania and niobia treated with phosphoric acid. Among these, ion exchange resins are preferred. The ion exchange resin is not particularly limited as long as it has Brønsted acid sites on the surface of the support, and examples include those having carboxyl groups and / or sulfonic acid groups. From the viewpoint of reactivity, strongly acidic cation exchange resins having sulfonic acid groups are preferred. From the viewpoint of catalyst recovery, sparingly soluble catalysts (also called heterogeneous catalysts) are preferred over water-soluble catalysts. These dehydration catalysts may be used individually or in any ratio and combination of two or more types.

[0041] Furthermore, the specific surface area of ​​the dehydration catalyst is 40 m². 2 It is preferable that it be 50m or more / g 2 It is more preferable that the amount be 1 / g or more. There is no particular upper limit, but it is usually 200m 2 It is less than or equal to / g, preferably 100m 2 The value is less than or equal to / g. Within this range, the probability of contact between the fructose produced from glucose and the dehydration catalyst becomes sufficient, and the efficiency of the dehydration reaction can be increased. The specific surface area of ​​the dehydration catalyst can be measured by permeation or gas adsorption.

[0042] <Mixed catalyst> The above isomerization catalyst and the above dehydration catalyst are brought into contact with the raw material glucose as a mixed catalyst. The specific manner in which the mixed catalyst is brought into contact with glucose is not particularly limited. A mixed catalyst, in which an isomerization catalyst and a dehydration catalyst are mixed substantially uniformly, may be brought into contact with glucose, or a catalyst in which isomerization catalysts and dehydration catalysts are alternately stacked may be packed into a column, and contact may be brought by passing a solution containing an organic solvent and glucose through it. In the case of liquid passage, one embodiment may be prepared by preparing separate lines for the organic solvent and the glucose solution, and having them merge before contact with the catalyst. Alternatively, the two-phase solvent, mixed catalyst, and glucose may be added to the reactor and reacted while stirring.

[0043] Using a mixed catalyst facilitates the isomerization and dehydration reactions compared to contacting the raw materials with individual catalysts. Furthermore, compared to methods in which the raw materials are sequentially contacted in an isomerization catalyst tank and a dehydration catalyst tank, it is advantageous in that only one reaction tank is used, thus shortening the reaction process.

[0044] In this embodiment, the mixing ratio of the isomerization catalyst and the dehydration catalyst is not particularly limited and is determined by considering the specific surface area of ​​each catalyst. Typically, the mass ratio is 1:3 to 3:1, preferably 1:3 to 1:2. Within this range, it is possible to rapidly dehydrate the fructose partially produced by the glucose isomerization reaction.

[0045] The ratio of the product of the specific surface area and catalyst amount of the isomerization catalyst to the product of the specific surface area and catalyst amount of the dehydration catalyst is not particularly limited. A ratio of 1:20 to 20:1 is preferred, 1:10 to 10:1 is more preferred, and 1:1 to 10:1 is particularly preferred. Within this range, it is possible to promote the isomerization reaction of glucose, which is the rate-limiting factor, and to rapidly dehydrate the partially produced fructose.

[0046] The amount of mixed catalyst used in this embodiment is not particularly limited. Typically, it is 0.01 g or more, preferably 0.1 g or more, and more preferably 0.5 g or more, per 1 g of glucose. Also, it is typically 10 g or less, preferably 5 g or less, and more preferably 3 g or less. If the amount of catalyst is above the lower limit, the reaction can proceed efficiently. If it is below the upper limit, costs can be reduced by reducing the amount of excess catalyst.

[0047] <glucose> The method for producing 5-HMF in this embodiment is characterized by contacting the above-mentioned mixed catalyst with glucose and causing a reaction. As the source of glucose, glucose itself (monosaccharide) may be used, or a sugar polymer (oligosaccharide or polysaccharide) containing glucose as a constituent sugar may be used. Furthermore, a derivative of glucose may be used as the source of glucose. There are no particular restrictions on the sugar polymers that contain glucose as a constituent sugar. Examples include sucrose, maltose, trehalose, turanose, isomaltulose, cellobiose, isomaltose, nigerose, maltulose, isomaltulose, genthiobiose, maltotriose, 1-kestose, maltooligosaccharide, dextrin, dextran, starch, cellulose, lactose, lactulose, mannan, and xyloglucan. Among these, sucrose and starch are preferred. When sugar polymers containing glucose as a constituent sugar are used as a source of glucose, glucose can be supplied while the sugar polymer is decomposed by a heating reaction, and further converted to 5-HMF by isomerization and intramolecular dehydration reactions using a mixed catalyst.

[0048] Glucose derivatives are not particularly limited as long as they have functional groups such as hydroxyl groups that are subjected to dehydration reactions, but examples include modified sugars such as amino sugars, etherified sugars, halogenated sugars, and phosphorylated sugars. Examples of such derivatives include glucosamine, glucosamine, and glucosamine. One example is -6-phosphate. Such derivatives can be converted to 5-HMF by pretreatment such as hydroxylation or reduction, while supplying glucose, and then by isomerization and intramolecular dehydration reactions using a mixed catalyst.

[0049] Furthermore, the glucose source may include hexoses other than glucose, either as a sugar polymer or monosaccharide. The hexoses other than glucose are not particularly limited, but fructose is preferred due to its reactivity, availability, and price. The glucose source described above preferably contains 10% by mass or more of glucose relative to the total sugar, more preferably 50% by mass or more, and particularly preferably 90% by mass or more, considering raw material cost and availability. According to the manufacturing method of this embodiment, even when using raw materials containing glucose within the above range, 5-HMF can be obtained with high yield and high selectivity, thus keeping manufacturing costs lower than when using fructose as a raw material.

[0050] In this embodiment, the glucose content in the glucose solution obtained by dissolving the glucose source in the above two-phase solvent is preferably 1% to 90% by mass, more preferably 3% to 80% by mass, and particularly preferably 5% to 70% by mass, relative to water. The glucose solution may also contain solid components consisting of undissolved sugars. The solid content concentration of the solution is preferably 1% to 85% by mass, more preferably 5% to 80% by mass, and particularly preferably 20% to 75% by mass. By using a solution with a solid content concentration below a certain level, the formation of sugar condensates as by-products can be further suppressed, and by using a solution with a solid content concentration above a certain level, the reaction can proceed efficiently.

[0051] The conditions for contacting the mixed catalyst with glucose are not particularly limited. The reaction temperature is preferably 80°C or higher, more preferably 100°C or higher. It is also preferably 200°C or lower, and more preferably 150°C or lower. If the reaction temperature is above the lower limit, the reaction can proceed efficiently. If it is below the upper limit, the generation of by-products can be suppressed and the degradation of the catalyst can be suppressed. The reaction time is not particularly limited, but is preferably 1 to 24 hours, and more preferably 2 to 10 hours. The reaction time can be appropriately set according to the reaction temperature. For example, if the reaction temperature is increased, the reaction rate will increase, and the reaction time can be shortened.

[0052] The reaction pressure is not particularly limited, but is preferably 0.01 MPa or higher, more preferably 0.1 MPa or higher, preferably 10 MPa or lower, and more preferably 1 MPa or lower. Within this range, the generation of by-products can be suppressed.

[0053] <Alkali metal salts or alkaline earth metal salts> In this embodiment, the two-phase solvent preferably contains 80 parts by mass or less of an alkali metal salt or alkaline earth metal salt per 100 parts by mass of glucose, usually 80 parts by mass or less, and more preferably 50 parts by mass or less. The lower limit is not particularly limited, but is usually 1 part by mass or more, and more preferably 0.01 parts by mass or more. Note that it is not necessary to contain an alkali metal salt or alkaline earth metal salt. Including the above amount of alkali metal salt or alkaline earth metal salt in the above two-phase solvent system is preferable because it may facilitate the oil-water separation described later. The alkali metal salt or alkaline earth metal salt is not particularly limited, and known salts can be used. Specifically, sodium chloride, potassium chloride, etc., can be mentioned.

[0054] <Oil / water separation> The manufacturing method of this embodiment may further include an oil-water separation step. The oil-water separation step is a step of separating the organic solvent phase from the aqueous phase, and is carried out for the purpose of separating the target compound, 5-HMF, from other substances from the reaction solution obtained by the above reaction. Specifically, organic The solvent phase contains oil-soluble components, mainly 5-HMF produced by the above reaction, while the aqueous phase contains water-soluble components such as sugar raw materials and catalysts. The method of oil-water separation is not particularly limited as long as it utilizes the difference in specific gravity between the organic solvent phase and the aqueous phase. For example, the reaction solution is placed in a separation tank and allowed to stand until the organic solvent phase and the aqueous phase separate. The specific standing time is not particularly limited, but is usually 0.1 hours or more, preferably 1 hour or more. Also, is usually 48 hours or less, preferably 24 hours or less.

[0055] When performing oil-water separation, the temperature is preferably between room temperature and 90°C, with a lower limit of 30°C being more preferable. The upper limit is more preferably 60°C, and even more preferably 40°C. Controlling the reaction temperature within this range improves extraction efficiency during recovery and shortens the working time.

[0056] In the manufacturing method of this embodiment, the reaction is carried out in a two-phase solvent system consisting of an organic solvent that is immiscible with water and water, thus shortening the time required for oil-water separation after the reaction. As a result, the generated 5-HMF is separated from the catalyst, preventing its degradation and enabling the production of 5-HMF in a higher yield than conventional methods. 5-HMF can be further separated and purified by distilling off the organic solvent from the organic solvent phase recovered by oil-water separation. During purification, processes such as centrifugation, drying, and extraction may be performed. At this time, the distilled organic solvent may be reused.

[0057] In oil-water separation, only the organic solvent phase may be recovered, and the aqueous phase may be discarded. Alternatively, the manufacturing method of this embodiment may include a step of recovering the aqueous phase. The aqueous phase contains water-soluble components such as sugar raw materials and catalysts. Sugars in the aqueous phase include those listed above as glucose sources and hexoses other than glucose, as well as sugars produced by their isomerization reactions and / or side reactions such as sugar condensation reactions. Specifically, these include glucose and fructose. The aqueous phase may be recovered, raw sugars added to the recovered aqueous phase, and then reintroduced into the 5-HMF production reactor. This process is preferable from the viewpoint of production cost because it allows for efficient use of unreacted raw sugars and allows for the direct use of the recovered catalyst. The recovered sugar and mixed catalyst may be further purified by processes such as centrifugation, drying, and extraction. The recovered sugar and mixed catalyst can be reused in the 5-HMF production reaction.

[0058] The 5-HMF obtained by the manufacturing method of this embodiment can be converted into derivatives as needed and then used as a raw material for biofuels, synthetic resins, fragrance components, physiologically active components, foods, pharmaceuticals, etc. Examples of derivatives include 2,5-dimethylfuran (DMF), 2,5-franzicarboxylic acid (FDCA), and 5-methoxymethylfurfural. Known methods can be used to produce the above derivatives.

[0059] Furthermore, the method of this embodiment can also be used to produce compounds from hexoses other than glucose through isomerization and dehydration reactions. The catalysts and reaction conditions used can be those described above.

[0060] <Second summary> Another embodiment of the present invention (second summary) is a method for producing a furan derivative having an acetal group and a carbonyl group, comprising a first oxidation step of contacting an HMF acetal with an oxidation catalyst. While methods for producing FDCA or frangic acid esters from HMF are disclosed in Patent Documents 3 and 4, etc., we have found that FDCA or frangic acid esters can be produced from HMF in high yield by a production method that goes through a furan derivative having an acetal group and a carbonyl group. In the method for producing FDCA or frangic acid esters from HMF, when the furan derivative is used, the following steps are included: That's fine. • Acetalization process to convert HMF into acetal • Deprotection process for furan derivatives having acetal groups and carbonyl groups, A recovery step for recovering the diol from the reaction solution after the deprotection step, • A second oxidation step in which the compound obtained in the deprotection step is oxidized. The following explains the process step by step.

[0061] <Acetalization process> The acetalization process involves acetalizing HMF. HMF can be obtained by derivation from biomass raw materials. For example, HMF can be obtained using known methods disclosed in Green Chemistry 16 (2014) 4816-4838, but is not limited to these methods. In one example, biomass raw materials can be subjected to known pretreatment and saccharification processes such as chemical treatment with acids or alkalis, biological treatment using microorganisms, or physical treatment to decompose (saccharify) the polysaccharides contained in the biomass raw materials into their constituent sugars, thereby obtaining a sugar solution containing oligosaccharides, disaccharides, and monosaccharides, and HMF can be obtained from this sugar solution.

[0062] Biomass raw materials include substances that are stored when sunlight energy is converted into starch, cellulose, hemicellulose, etc., through the photosynthesis of plants, as well as products made by processing plant materials. Examples of biomass raw materials include wood, rice straw, rice husks, rice bran, old rice, corn, sugarcane, cassava, sago palm, cardoon, switchgrass, pine wood, poplar wood, maple wood, okara (soy pulp), corn cob, corn stover, corn fiber, tapioca, bagasse, vegetable oil cake, potatoes, buckwheat, soybeans, waste paper, papermaking residue, fishery residue, livestock waste, sewage sludge, and food waste. Among these, plant resources such as wood, rice straw, rice husks, rice bran, old rice, corn, sugarcane, cassava, sago palm, cardoon, switchgrass, pine wood, poplar wood, maple wood, okara, corn cob, corn stover, corn fiber, tapioca, bagasse, vegetable oil cake, potato, buckwheat, soybean, waste paper, papermaking residue, and food waste are preferred, and more preferably wood, rice straw, rice husks, old rice, corn, sugarcane, cassava These include sava, sago palm, cardoon, switchgrass, pine wood, poplar wood, maple wood, corn cob, corn stover, corn fiber, bagasse, potatoes, waste paper, papermaking residue, and food waste, most preferably corn, sugarcane, cassava, sago palm, bagasse, cardoon, switchgrass, pine wood, poplar wood, maple wood, corn cob, corn stover, corn fiber, waste paper, papermaking residue, and food waste.

[0063] The sugars derived from the above-mentioned biomass raw materials typically include hexoses such as glucose, mannose, galactose, fructose, sorbose, and tagatose, as well as disaccharides, oligosaccharides, and polysaccharides such as saccharose, starch, cellulose, and hemicellulose. Among these, glucose and fructose are preferred due to their high reaction yield. On the other hand, cellulose and hemicellulose are preferred as sugars derived from plant resources in a broader sense.

[0064] Acetalization is usually carried out in a solvent. The solvent may contain a catalyst, and from the viewpoint of carrying out the reaction in a short time, it is preferable to contain a solid catalyst that is insoluble in the solvent and carry out the reaction in a heterogeneous system. Preferred catalysts include acidic cation exchange resins such as amberlist, amberlite, and diaion; zeolites; metal oxides and metal composite oxides such as Nb2O5, YNbO4, Ta2O5, Nb2O5-WO3, Nb2O5-MoO3, TiO2-WO3, TiO2-MoO3, SiO2-Nb2O5, and SiO2-Ta2O5; clay; sulfuric acid-immobilized catalysts such as sulfurized ZrO2; and phosphoric acid-immobilized catalysts such as titania and niobia treated with phosphoric acid. Among these, acidic cation exchange resins such as Amberlist, Amberlite, and Diaion, zeolites, Nb2O5, Nb2O5-WO3, and Nb2O5-MoO3 are more preferred, and in particular, acidic cation exchange resins such as Amberlist, Amberlite, and Diaion are preferred, for the reason that they selectively allow only the acetalization reaction of HMF to proceed. preferable.

[0065] These catalysts may be used individually or in combination of two or more types. When two or more catalysts are used, the combination is not particularly limited, and the catalysts used in the combination may be co-catalysts in which the metal has catalytic activity, or co-catalysts that enhance the catalytic activity of the other metals.

[0066] While water or organic solvents are typically used as solvents, it is sometimes preferable to use a mixed solvent combining water and an organic solvent. From a cost-effectiveness standpoint, it is preferable to use a single solvent as the reaction solvent.

[0067] The organic solvent used is not particularly limited, but examples include ethers with 4 to 20 carbon atoms such as diethyl ether, tetrahydrofuran (THF), tetrahydropyran, methyltetrahydropyran, dipropyl ether, diisopropyl ether, methyl-tert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, etc.; 2-butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone Ketones with 4 to 20 carbon atoms, such as cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, 3-dodecanone, 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, acetophenone, etc.; esters such as ethyl acetate, propyl acetate, and butyl acetate;Methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 1-heptanol, 2-heptanol, 1-octanol, 2-octanol, 3-octanol, 2-ethyl-1-hexanol Monoalcohols with 1 to 20 carbon atoms, such as 1-nonanol, 1-decanol, 1-undecyl alcohol, 1-lauryl alcohol, 1-tridecyl alcohol, 1-tetradecanol, 1-pentadecyl alcohol, 1-hexadecanol, cis-9-hexadecene-1-ol, 1-heptadecanol, 1-octadecanol, 16-methylheptadecene-1-ol, nonadecyl alcohol, arachidyl alcohol, etc.; ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,3- Diols with 1 to 6 carbon atoms, such as tandiol, 1,3-pentanediol, 1,2-propanediol, 1,2-butanediol, and 1,2-pentanediol; phenols with 6 to 12 carbon atoms, such as phenol, methylphenol, ethylphenol, propylphenol, and butylphenol; saturated aliphatic hydrocarbon compounds with 3 to 12 carbon atoms, such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, dodecane, and isododecane; toluene, xylene, trimethylbenzene, and 1,2,3,4-tetrahydrona Aromatic hydrocarbons such as phthalene and 1-methylnaphthalene; lactones such as γ-butyrolactone and γ-valerolactone; halogenated hydrocarbons such as dichloromethane, chloroform, dichloroethane, tetrachloroethane, and hexachloroethane; and others such as dimethylacetamide, N,N-dimethylformamide, N-methylmorpholine, N-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, hexamethyltriamide, tetramethylurea, dimethyl sulfoxide, sulfolane, isosorbide, and isosorbide. Examples include rubidodimethyl ether, propylene carbonate, and mixtures thereof. Other ionic liquids that may be used include, for example, pyrrolidinium salts such as 1-butyl-1-methylpyrrolidinium bromide; piperidinium salts such as 1-butyl-1-methylpiperidinium triflate; pyridinium salts such as 1-butylpyridinium tetrafluoroborate; imidazolium salts such as 1-ethyl-3-methylimidazolium chloride; ammonium salts such as tetrabutylammonium chloride; phosphonium salts such as tetrabutylphosphonium bromide; and sulfonium salts such as triethylsulfonium bis(trifluoromethanesulfonyl)imide.

[0068] Among these, the organic solvent is preferably selected from at least one of the group consisting of ethers, ketones, diols, esters, lactones, aromatic hydrocarbons, halogenated hydrocarbons, and saturated aliphatic hydrocarbons, more preferably selected from at least one of the group consisting of ethers, ketones, diols, aromatic hydrocarbons, and saturated aliphatic hydrocarbons, and even more preferably selected from at least one of the group consisting of ethers, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons. Specifically, methyltetrahydropyran, 2-butanone (methyl ethyl ketone), 4-methyl-2-pentanone (methyl isobutyl ketone), and toluene are preferred.

[0069] In the acetalization process, a diol is usually added to acetalize HMF, but any alcohol having two or more hydroxyl groups is acceptable, such as a trihydric alcohol like glycerin or a tetrahydric alcohol like erythritol. Catechol is also suitably used. The diol to be added is appropriately determined according to the type of acetal intermediate to be produced, and is preferably a diol having 2 to 10 carbon atoms. Examples include ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,3-pentanediol, 1-phenyl-1,3-propanediol, 2-phenyl-1,3-propanediol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1-phenyl-ethylene glycol. Among these diols, those forming a six-membered ring structure are preferred because they improve the stability of the acetal intermediate. Specifically, examples include 1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,3-pentanediol, 1-phenyl-1,3-propanediol, and 2-phenyl-1,3-propanediol. It is possible to use two or more diols, but usually only one is used.

[0070] Furthermore, a diol may be used as the organic solvent. When a diol is used as the organic solvent, it is preferable that it be in a liquid state at room temperature. In this case, acetalization of HMF can be carried out without adding a diol separately to the organic solvent. When a diol is used as the organic solvent, specific examples include ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,3-butanediol, 1,3-pentanediol, 1,2-propanediol, 1,2-butanediol, and 1,2-pentanediol.

[0071] The reaction method in the acetalization process can be carried out using batch or flow methods. The materials in contact with the fluid, such as the reactor and flow channels, are not particularly limited to glass, stainless steel (SUS), iron, or other metals. However, glass or stainless steel (SUS) are preferred due to their corrosion resistance and high energy transfer efficiency. Furthermore, from the perspective of industrial manufacturing equipment costs, stainless steel (SUS) is preferred.

[0072] Furthermore, in the acetalization process, a membrane may be placed in the reaction system, and the acetalization reaction may be carried out while dehydrating the reaction system using reaction separation. There are no restrictions on the membrane placed in the reaction system, but examples include zeolite membranes, silica membranes, and carbon membranes. In order to selectively remove water, it is preferable to use a hydrophilic zeolite membrane having a certain pore size corresponding to the diameter of water molecules. Zeolite membrane types include FAU type, BEA type, MOR type, MFI type, FER type, LTA type, CHA type, and DDR type, but LTA type (pore size approximately 4 Å), CHA type (pore size approximately 3.8 Å), and DDR type (pore size approximately 3.2 Å), which have pore sizes close to the diameter of water molecules (approximately 2.7 Å), are preferably used in dehydration. The silica (SiO2) / alumina (Al2O3) ratio of the zeolite membrane is preferably in the range of 2 to 40, and more preferably 2 to 20. Selecting a film with a silica / alumina ratio within this range is preferable because it offers good film stability (acid resistance), is hydrophilic, and has high dehydration capacity.

[0073] The reaction temperature in the acetalization step is preferably between room temperature and 120°C, with a lower limit of 30°C being more preferable, and 40°C being even more preferable. The upper limit is more preferably 100°C, and 80°C being even more preferable. By controlling the reaction temperature within this range, it is possible to suppress prolonged reaction times, concurrent side reactions, runaway reactions, and discoloration of the product. In the acetalization process, the reaction time in the batch method is typically 1 minute to 30 hours, preferably 10 minutes to 20 hours, and more preferably 30 minutes to 15 hours, starting from the time stirring begins. By controlling the reaction time within this range, the occurrence of side reactions and discoloration of the product can be suppressed. However, this does not apply to the reaction time when a flow method is used. The reaction pressure in the acetalization process is not particularly limited, but is usually atmospheric pressure.

[0074] <First oxidation step> In the first oxidation step, HMF acetal is oxidized to synthesize a furan derivative having an acetal group and a carbonyl group. This oxidation step includes oxidative esterification. In this embodiment, in the first oxidation step, a furan derivative having an acetal group and a carbonyl group is synthesized by contacting an HMF acetal with an oxidation catalyst. The furan derivative is preferably a compound represented by the following formula (1), more preferably a compound represented by the following formula (2), and even more preferably a compound represented by the following formula (4). [ka]

[0075] In formula (1), Z is a hydrogen atom or a hydroxyl group, and R 2 and R 3 This is independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent. Examples of alkyl substituents include C1-C6 alkyl groups. [ka] In formula (2), R 2 and R 3 This is independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent. [ka]

[0076] The oxidation of HMF acetals is carried out in the presence of a catalyst, and examples of catalysts include metals from Groups 8 to 10 of the periodic table and their compounds, such as platinum, palladium, nickel, iron, ruthenium, and cobalt; metals from Group 11 of the periodic table and their compounds, such as copper, silver, and gold; metals from Group 12 of the periodic table and their compounds, such as zinc; metals from Group 13 of the periodic table and their compounds, such as indium; metals from Group 14 of the periodic table and their compounds, such as tin and lead; metals from Group 7 of the periodic table and their compounds, such as manganese and rhenium; metals from Group 6 of the periodic table and their compounds, such as chromium and molybdenum; metals from Group 5 of the periodic table and their compounds, such as niobium and tantalum; metals from Group 4 of the periodic table and their compounds, such as zirconium; metals from Group 3 of the periodic table and their compounds, such as scandium; metals from Group 2 of the periodic table and their compounds, such as magnesium and calcium; metals from Group 1 of the periodic table and their compounds, such as cesium; and mixtures (including alloys) of these metals. Metals and compounds of groups 6-12 of the periodic table, as well as mixtures thereof (including alloys), are particularly preferred, and metals and compounds of groups 7-11 of the periodic table are even more preferred, with platinum, palladium, rhenium, magnesium, copper, silver, gold, zinc, manganese, cobalt, and their compounds being particularly preferred, and platinum, palladium, rhenium, copper, silver, gold, cobalt, manganese, and their compounds being the most preferably used. Examples of compounds include oxides of these metals, alkoxy compounds, alkyl compounds, and organic acid salts, but metals and metal oxides or organic acid salts are preferred. These metals and their compounds may be mixtures, and for example, a catalyst consisting of a combination of a cobalt compound, a manganese compound, and a bromine compound may also be used.

[0077] Furthermore, these metal catalysts are preferably used as metal-supported catalysts supported on various carriers. Examples of carriers include carbon, silica, alumina, titania, zirconia, niobia, ceria, tungsten oxide, silicon carbide, boron carbide, titanium carbide, diatomaceous earth, and natural minerals such as layered silicates. Among these, carbon, titania, and ceria are preferred in terms of ease of catalyst preparation and activity. These catalysts may be used individually, in combination of two or more, or added later.

[0078] In this process, the oxidation reaction of HMF acetal in the presence of a metal catalyst can be carried out using a batch method or a flow method, but it is preferable to adopt the flow method due to its higher production efficiency.

[0079] When the oxidation reaction is carried out in a batch manner, the amount of catalyst used is preferably 0.002 ppm by mass or more and 100,000 ppm by mass in terms of metal equivalent relative to the raw materials. The lower limit of the amount of catalyst used is more preferably 0.02 ppm by mass, even more preferably 0.2 ppm by mass, and particularly preferably 2 ppm by mass, in terms of metal equivalent relative to the raw materials. The upper limit of the amount of catalyst used is more preferably 50,000 ppm by mass, even more preferably 20,000 ppm by mass, and particularly preferably 10,000 ppm by mass, in terms of metal equivalent relative to the raw materials. By adopting such amounts of catalyst, the furan derivative can be produced efficiently in a moderate reaction time, while suppressing the increase in catalyst costs and the discoloration of the product. The amount of catalyst used when employing a flow method is not limited to these amounts.

[0080] In this process, the presence of a base can improve the stability of the acetal, suppress side reactions, and potentially increase the yield of the desired product. Therefore, the oxidation reaction may be carried out in the presence of a base. Examples of such bases include inorganic bases such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, and potassium bicarbonate, as well as organic bases such as triethylamine. Among these, inorganic bases are preferred due to their efficient removal from the product.

[0081] The amount of base used when carrying out the oxidation reaction in the presence of a base is not particularly limited, but the lower limit is 0.01 equivalents or more, preferably 0.1 equivalents or more, relative to the HMF acetal, and the upper limit is 10 equivalents or less, preferably 5 equivalents or less, more preferably 3 equivalents or less. By using such amounts, the stability of the HMF acetal can be improved and side reactions can be suppressed, and the yield of the target product can be improved. The reaction temperature in this process is preferably between room temperature and 200°C, with a lower limit of 30°C, even more preferably 40°C, and particularly preferably 60°C. The upper limit is more preferably 180°C, even more preferably 150°C, particularly preferably 130°C, and most preferably 80°C. By controlling the reaction temperature within this range, it is possible to suppress prolonged reaction times, concurrent side reactions, decomposition of the diol acting as the acetalizing agent, runaway reactions, and discoloration of the product.

[0082] The oxygen source used in the oxidation reaction is not particularly limited and can include oxygen-containing organic compounds, inorganic peroxides, or oxygen-containing gases. However, an oxygen-containing gas such as oxygen gas or air that does not require separation and purification after the reaction is usually used. In the batch method, the oxygen-containing gas is confined within the reactor, while in the flow method, the oxygen-containing gas is circulated within the reactor to carry out the oxidation reaction. The flow method is preferred.

[0083] When using an oxygen-containing gas, the oxygen content in the gas is usually 20% by volume or more, and may be 50% by volume or more. Pure oxygen (99% or more) may also be used. From the viewpoint of reducing the risk of explosion and ensuring reaction safety, it is preferable to use air containing approximately 21% by volume of oxygen, or an oxygen-containing gas with a composition almost identical to air. By using such an oxygen-containing gas, not only can the reaction selectivity be improved, but the oxidative decomposition reaction of the diol necessary to obtain the cyclic acetal of HMF can also be suppressed.

[0084] The reaction time in this process is not particularly limited when the oxidation reaction is carried out in a flow manner. When the oxidation reaction is carried out in a batch manner, the reaction time is taken as the starting point from the time when the oxygen-containing gas is first introduced into the reactor, and is usually 10 minutes to 30 hours, preferably 30 minutes to 20 hours, more preferably 1 hour to 10 hours, and even more preferably 1 hour to 5 hours. By controlling the reaction time within this range, the occurrence of side reactions and runaway reactions can be suppressed, and manufacturing costs can be reduced.

[0085] When carrying out an oxidation reaction using a flow-through method, the rate at which oxygen-containing gas is circulated into the reactor is as follows: The flow rate is typically 1 mL / min to 100 L / min, preferably 10 mL / min to 10 L / min, more preferably 100 mL / min to 5 L / min, and even more preferably 500 mL / min to 1 L / min. By controlling the flow rate within this range, the oxygen consumption efficiency and the production efficiency of the target product are improved, side reactions and runaway reactions are suppressed, and manufacturing costs can be reduced.

[0086] Methods for circulating oxygen-containing gas into the reactor include blowing the oxygen-containing gas into the liquid phase of the reactor or blowing it into the gas phase of the reactor, but the preferred method is blowing it into the liquid phase of the reactor. The oxygen-containing gas may be circulated continuously or intermittently, but continuous circulation is preferred. When circulating intermittently, it is preferable to appropriately adjust the interval of intermittent circulation so that oxygen does not become deficient. Alternatively, the oxygen-containing gas may be supplied to pressurize the reaction vessel and carry out the oxidation reaction. The reaction pressure in this case is usually 0.1 MPa or higher, preferably 0.3 MPa or higher, more preferably 0.4 MPa or higher, and usually 15 MPa or lower, preferably 10 MPa or lower, more preferably 5 MPa or lower, even more preferably 3 MPa or lower, and particularly preferably 1 MPa or lower. By controlling the pressure within this range, high-pressure reaction equipment becomes unnecessary, and the occurrence of side reactions and the oxidative decomposition reaction of the diol necessary to obtain the cyclic acetal of HMF can be suppressed.

[0087] The reaction solvent in this process is not particularly limited, but it is preferably a solvent containing water to dissolve the HMF acetal raw material. In this case, a mixed solvent of the reaction solvent and water from the acetalization process described above, a mixed solvent of the diol and water described above, or water alone can be used. When oxidation is performed after isolating the cyclic acetal intermediate, the solvent does not necessarily have to be a mixed solvent, and a water solvent may be used. Here, when using a mixed solvent with water, the water content is not particularly limited as long as it is 1 equivalent or more relative to the cyclic acetal intermediate, but usually, the lower limit as a volume ratio is 1% by volume or more, preferably 10% by volume or more, more preferably 50% by volume or more, and there is no upper limit.

[0088] The concentration of HMF acetal in the reaction solvent introduced into the reactor is typically 1% by mass at the lower limit, preferably 5% by mass, more preferably 10% by mass, even more preferably 20% by mass, and particularly preferably 30% by mass, with an upper limit of typically 60% by mass, preferably 50% by mass. By controlling the concentration within this range, it is possible to avoid using excessively large reaction vessels and to carry out the reaction in a short time with high production efficiency. Furthermore, side reactions such as the decomposition reaction of HMF acetal can be suppressed.

[0089] Furthermore, if the oxidation in this process is oxidative esterification, the presence of an alcohol in the reaction system will produce an ester of formylfuran carboxylic acid (FFCA) acetal. If the alcohol present is a diol added in the acetalization step, a hydroxyalkyl ester of FFCA acetal will be produced; if it is a monool, an alkyl ester of the acetal will be produced. The alcohol present is not particularly limited, but includes methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 1-heptanol, 2 -Heptanol, 1-octanol, 2-octanol, 3-octanol, 2-ethyl-1-hexanol, 1-nonanol, 1-decanol, 1-undecyl alcohol, 1-lauryl alcohol, 1-tridecyl alcohol, 1-tetradecanol, 1-pentadecyl alcohol, 1-hexadecanol, cis-9-hexadecene-1-ol, 1-heptadecanol, 1-octadecanol, 16-methylheptadecene-1-ol, nonadecyl alcohol, araki It may also be an aliphatic monoalcohol having 1 to 20 carbon atoms, such as dialdehyde, or an aliphatic diol having 2 to 8 carbon atoms, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or 1,4-cyclohexanedimethanol.

[0090] The reaction solution obtained after oxidizing the HMF acetal contains a furan derivative having an acetal group and a carbonyl group. In the reaction solution, the concentration of the furan derivative in the total compounds having a furan skeleton is preferably 70 mol% or more, and more preferably 90 mol% or more. That is, another embodiment of the present invention is a solution containing a furan derivative having an acetal group and a carbonyl group, wherein the concentration of the furan derivative in the total compounds having a furan skeleton is 70 mol% or more. Since the aforementioned furan derivative is a compound with high thermal stability, controlling it within this range has the effect of suppressing the decomposition of the compound containing the furan skeleton in the reaction solution during the deprotection step and the second oxidation step described later.

[0091] <Deprotection process> The deprotection step involves deprotecting the furan derivative having an acetal group and a carbonyl group obtained in the oxidation step by a hydrolysis reaction to synthesize diformylfuran, FFCA, or its ester. The inclusion of this deprotection step makes it possible to easily produce FDCA and FDCA esters even under mild conditions. Here, the deprotection of the furan derivative can be carried out by a hydrolysis reaction under acidic conditions. Another aspect of this embodiment is a method for producing a furan derivative, comprising a deprotection step of synthesizing a furan derivative by deprotecting an acetal-protected FFCA (formylfuranic acid) acetal or ester thereof, wherein the furan derivative is one or more selected from the group consisting of formylfuranic acid and its esters. While methods for producing FDCA or frangic acid esters from HMF are disclosed in Patent Documents 3 and 4, we have discovered that a method for deprotecting FFCA acetal or its ester can produce FDCA or its ester, i.e., frangic acid ester, from HMF in high yield.

[0092] The deprotection step involves deprotecting FFCA acetal or its ester by hydrolysis to synthesize FFCA or its ester. This step makes it possible to easily produce FDCA and FDCA esters even under mild conditions. Here, the deprotection of FFCA acetal or its ester can be carried out by hydrolysis under acidic conditions.

[0093] In this embodiment, in the deprotection step, FFCA acetal or its ester is deprotected to synthesize FFCA or its ester. The FFCA acetal or its ester used in the deprotection step is not particularly limited, but is preferably a compound having a cyclic acetal structure of a 5-membered ring or a 6-membered ring. The FFCA acetal is preferably a compound represented by the following formula (3). [ka] In formula (3), X, R 4 and R 5 This is independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent. Examples of alkyl substituents include C1-C6 alkyl groups.

[0094] The reaction method in the deprotection process can be implemented using batch or flow methods. The wetted materials for reactors and flow channels are not particularly limited to glass, stainless steel (SUS), iron, or other metals, but glass or stainless steel (SUS) are preferred due to their corrosion resistance and high energy transfer efficiency. Furthermore, from the perspective of industrial manufacturing equipment costs, stainless steel (SUS) is preferred. The hydrolysis conditions are not particularly limited as long as they allow the hydrolysis of the furan derivative to proceed, and the pH is preferably in the range of 0.1 to 7.

[0095] The reaction temperature in hydrolysis is preferably between room temperature and 120°C, with a lower limit of 30°C and an even higher limit of 40°C. The upper limit of the reaction temperature is more preferably 100°C and an even higher limit of 80°C. By controlling the reaction temperature within this range, it is possible to suppress prolonged reaction times, side reactions, runaway reactions, and product discoloration. In the case of a batch hydrolysis, the reaction time is typically 1 minute to 30 hours, preferably 10 minutes to 20 hours, and more preferably 30 minutes to 15 hours, starting from the time stirring begins. By controlling the reaction time within this range, it is possible to suppress the occurrence of side reactions and discoloration of the product. This does not apply to the flow-through method. The reaction pressure in hydrolysis is not particularly limited, but is usually atmospheric pressure.

[0096] While water is typically used as the solvent in hydrolysis, a mixed solvent of water and an organic solvent may also be used. From the viewpoint of hydrolysis efficiency and cost advantages, it is preferable to use water as the reaction solvent. When using a mixed solvent of water and an organic solvent, the organic solvent is not particularly limited, but examples include ethers with 4 to 20 carbon atoms such as diethyl ether, tetrahydrofuran (THF), tetrahydropyran, methyltetrahydropyran, dipropyl ether, diisopropyl ether, methyl-tert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, etc.; 2-butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, 2-hexanone Ketones with 4 to 20 carbon atoms, such as 3-hexanone, cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, 3-dodecanone, 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, acetophenone, etc.; esters such as ethyl acetate, propyl acetate, and butyl acetate;Methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 1-heptanol, 2-Heptanol, 1-Octanol, 2-Octanol, 3-Octanol, 2-Ethyl-1-Hexanol, 1-Nonanol, 1-Decanol, 1-Undecyl Alcohol, 1-Lauryl Alcohol, 1-Tridecyl Alcohol, 1-Tetradecanol, 1-Pentadecyl Alcohol, 1-Hexadecanol, cis-9-Hexadecen-1-ol, 1-Heptadecanol, 1-Octadecanol, 16-Methic; Monoalcohols with 1 to 20 carbon atoms, such as heptadecene-1-ol, nonadecyl alcohol, and arachidyl alcohol; phenols with 6 to 12 carbon atoms, such as phenol, methylphenol, ethylphenol, propylphenol, and butylphenol; saturated aliphatic hydrocarbon compounds with 3 to 12 carbon atoms, such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, dodecane, and isododecane; aromatic hydrocarbons such as toluene, xylene, trimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene; γ-butyl Examples include lactones such as loractone and γ-valerolactone; halogenated hydrocarbons such as dichloromethane, chloroform, dichloroethane, tetrachloroethane, and hexachloroethane; and other substances such as dimethylacetamide, N,N-dimethylformamide, N-methylmorpholine, N-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphate triamide, tetramethylurea, dimethyl sulfoxide, sulfolane, isosorbide, isosorbide dimethyl ether, propylene carbonate, and mixtures thereof. In addition, ionic liquids such as pyrrolidinium salts including 1-butyl-1-methylpyrrolidinium bromide; piperidinium salts including 1-butyl-1-methylpiperidinium triflate; pyridinium salts including 1-butylpyridinium tetrafluoroborate; imidazolium salts including 1-ethyl-3-methylimidazolium chloride; ammonium salts including tetrabutylammonium chloride; phosphonium salts including tetrabutylphosphonium bromide; and sulfonium salts including triethylsulfonium bis(trifluoromethanesulfonyl)imide may also be used.

[0097] As catalysts for hydrolysis, acidic cation exchange resins such as Amberlist, Amberlite, and Diaion, zeolites, metal oxides and metal composite oxides such as Nb2O5, YNbO4, Ta2O5, Nb2O5-WO3, Nb2O5-MoO3, TiO2-WO3, TiO2-MoO3, SiO2-Nb2O5, and SiO2-Ta2O5, clay, sulfuric acid-immobilized catalysts such as sulfurized ZrO2, and phosphoric acid-immobilized catalysts such as titania and Niobia treated with phosphoric acid are preferred. Among these, acidic cation exchange resins such as Amberlist, Amberlite, and Diaion, and zeolites are more preferred in that they selectively allow only the deprotection of HMF acetal in a water-containing solvent, and acidic cation exchange resins such as Amberlist, Amberlite, and Diaion are particularly preferred.

[0098] The reaction solution obtained by hydrolyzing the furan derivative contains diformylfuran, FFCA, or its ester. In this reaction solution, the concentration of diformylfuran, FFCA, and its ester is preferably 70 mol% or more, and more preferably 90 mol% or more, among all compounds having a furan skeleton. In particular, since FFCA and its ester are compounds with high thermal stability, controlling the concentration within this range can suppress the decomposition of compounds containing a furan skeleton in the reaction solution during the second oxidation step described later.

[0099] <Recovery Process> In the deprotection step, the reaction solution obtained when a furan derivative having an acetal group and a carbonyl group is deprotected to synthesize diformylfuran, FFCA, or its ester may be subjected to a recovery step to recover the diol from the reaction solution. The recovered diol is the diol added in the acetalization step. The method for recovering the diol from the reaction solution is not particularly limited and can be recovered by extraction, distillation, or other means. When extraction is performed in the recovery process, the temperature is preferably above room temperature and below 90°C, with a lower limit of 30°C being more preferable. The upper limit is more preferably 60°C, and even more preferably 40°C. By controlling the reaction temperature within this range, the extraction efficiency during recovery is improved, and the working time can be shortened.

[0100] While organic solvents are typically used as extraction solvents, a mixed solvent of water and an organic solvent may also be used. From a cost-effectiveness standpoint, it is preferable to use a single solvent as the extraction solvent. . The aforementioned organic solvents are not particularly limited, but examples include ethers with 4 to 20 carbon atoms such as diethyl ether, tetrahydropyran, methyltetrahydropyran, dipropyl ether, diisopropyl ether, methyl-tert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether; 2-butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, and 3-dodecanone. , 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, acetophenone and other ketones with 4 to 20 carbon atoms; esters such as ethyl acetate, propyl acetate, and butyl acetate; pentane, hexane, cyclohexa Saturated aliphatic hydrocarbon compounds having 3 to 12 carbon atoms, such as nitrates, heptane, octane, nonane, decane, dodecane, and isododecane; aromatic hydrocarbons such as toluene, xylene, trimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene; lactones such as γ-butyrolactone and γ-valerolactone; and halogenated hydrocarbons such as dichloromethane, chloroform, dichloroethane, tetrachloroethane, and hexachloroethane may be used. Among these, the organic solvent is preferably selected from at least one of the group consisting of ethers, ketones, esters, lactones, aromatic hydrocarbons, halogenated hydrocarbons, and saturated aliphatic hydrocarbons, more preferably from at least one of the group consisting of esters, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons, and even more preferably esters.Furthermore, ethyl acetate is specifically preferred as the ester.

[0101] The recovery process is carried out using methods such as batch processing or flow processing. The materials in contact with the fluid, such as reactors and flow paths, are not particularly limited to glass, stainless steel (SUS), iron, or other metals. However, glass or stainless steel (SUS) materials are preferred due to their corrosion resistance and high energy transfer efficiency. Furthermore, from the perspective of industrial manufacturing equipment costs, stainless steel (SUS) materials are preferred.

[0102] <Second oxidation step> The second oxidation step involves oxidizing the diformylfuran, FFCA, or their esters obtained in the deprotection step. This oxidation step includes oxidative esterification. FDCA is obtained by oxidation of these compounds, and FDCA esters are obtained by oxidative esterification. Another aspect of this embodiment is a method for producing franciocarboxylic acid or its ester, comprising a second oxidation step of contacting a composition containing a furan derivative with an oxidation catalyst, wherein the furan derivative is one or more selected from the group consisting of diformylfuran, formylfurancarboxylic acid and its esters, and the concentration of the furan derivative in the total compounds having a furan skeleton contained in the composition containing the furan derivative is 70% by mass or more. While methods for producing FDCA or franca carboxylic acid esters from HMF are disclosed in Patent Documents 2 and 3, we have found that a method including a step of oxidizing a high concentration of the furan derivative can produce FDCA or franca carboxylic acid esters from HMF in high yield. Among the compositions subjected to the second oxidation step, among all compounds having a furan skeleton, diformyl furan It is preferable that the concentration of FFCA and its ester is 70 mol% or more, and more preferably 90 mol% or more. Among these compounds having a furan skeleton, particularly, since FFCA and its ester are compounds with high thermal stability, by controlling within this range, the effect of suppressing the decomposition of the compound containing a furan skeleton in the reaction solution can be achieved.

[0103] In the second oxidation step, since the oxidation of the formyl group proceeds easily, from the viewpoint of suppressing the concurrent occurrence of side reactions, the reaction can be carried out at a temperature lower than the reaction temperature in the second oxidation step. Specifically, it may be 80 °C or lower, or may be 60 °C or lower. Also, the lower limit value of the reaction temperature in the second oxidation step may be the same as the lower limit value of the reaction temperature in the oxidation step. Thus, the second oxidation step can carry out the oxidation reaction under milder conditions compared to the oxidation step. Regarding the reaction conditions other than the reaction temperature in the second oxidation step, they are the same as the conditions described in the first oxidation step.

[0104] <Method for recovering FDCA and FDCA ester> The recovery of FDCA and FDCA ester obtained in the above second oxidation step is not particularly limited, and the product can be recovered by a solvent distillation method, an extraction method with an organic solvent after solvent distillation, a distillation method, a sublimation method, a crystallization method, or a chromatography method. Among these, a method of recovering while purifying the product by a distillation method is preferable.

[0105] [[ID=十六]]Also, as another aspect of this embodiment, the following production method can also be mentioned. That is, a method for producing a furandicarboxylic acid or a furandicarboxylic acid ester from hydroxymethylfurfural, which has the following production steps (i) to (iv). (i) An acetalization step of acetalizing hydroxymethylfurfural to synthesize hydroxymethylfurfural acetal, (ii) A first oxidation step of oxidizing hydroxymethylfurfural acetal to synthesize formylfurancarboxylic acid acetal or its ester, (iii) Deprotecting formylfuranate acetal or its ester A deprotection step for synthesizing refranic acid or its ester, and (iv) A second oxidation step of oxidizing formylfuranic acid or its ester. Furthermore, the process may include a recovery step, which will be described later, after step (iii).

[0106] The above-mentioned formylfuran acetal or its ester is preferably a compound represented by formula (3). [ka] In formula (3), X, R 2 and R 3 (These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.) Furthermore, in step (i), it is preferable to use an organic solvent selected from 2-butanone (methyl ethyl ketone), 4-methyl-2-pentanone (methyl isobutyl ketone), toluene, and methyltetrahydropyran, and it is preferable to have a recovery step after step (iii) in which the diol is recovered from the reaction solution, and it is preferable that the diol is a diol having 2 to 10 carbon atoms. [Examples]

[0107] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples unless it exceeds the essence of the invention.

[0108] <<Example A>> The yield of the product was determined by diluting the post-reaction solution and quantitatively measuring the product using the absolute calibration curve method with liquid chromatography (Shimadzu Corporation: LC-2010, column: ULTRON PS-80H). A differential refractive index detector (RI detector) was used, and water was the developing solvent. The yield of 5-hydroxymethylfurfural (5-HMF) was determined by the following formula. Selectivity of 5-HMF (%) = Moles of 5-HMF produced / Moles of glucose consumed in the reaction × 100 5-HMF yield (%) = Moles of 5-HMF produced / Moles of glucose used in the reaction × 100

[0109] [Example A1] Glucose (0.3g, 1.7 mmol), aluminum oxide (Al2O3) (0.3g, 100 wt%) relative to the substrate as an isomerization catalyst, and a hyperporous type strongly acidic cation exchange resin (Diaion) as a dehydration catalyst. TM 0.6 g of RCP160M (200 wt%) relative to the substrate was placed in a pressure vessel, and 7 g of methyltetrahydropyran (MTHP) and 3 g of water were added and the vessel was sealed. The vessel was heated to 120°C and heated under a pressure of 0.2 MPa with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0110] [Example A2] Glucose (0.3g, 1.7 mmol), aluminum oxide (Al2O3) (0.3g, 100 wt%) relative to the substrate as an isomerization catalyst, and a hyperporous type strongly acidic cation exchange resin (Diaion) as a dehydration catalyst. TM 0.6 g of RCP160M (200 wt%) relative to the substrate was placed in a pressure vessel, and 7 g of methyl isobutyl ketone (MIBK) and 3 g of water were added and the vessel was sealed. The vessel was heated to 120°C and heated under a pressure of 0.2 MPa with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0111] [Example A3] Glucose (1.0g, 5.7 mmol) and aluminum oxide (Al) as an isomerization catalyst. 2 O 3 ) (1.0 g, 100 wt%) relative to the substrate) and a hypoporous type strongly acidic cation exchange resin (Diaion TMRCP160M) (2.0 g, 200 wt%) relative to the substrate were placed in a pressure vessel, and methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0112] [Example A4] Glucose (1.0g, 5.7 mmol) and aluminum oxide (A) as an isomerization catalyst. 1.0 g of l₂O₃ (100 wt%) relative to the substrate and a porous type strongly acidic cation exchange resin (Amberlyst® 15) (2.0 g, 200 wt%) relative to the substrate were placed in a pressure vessel, and methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0113] [Example A5] Glucose (1.0 g, 5.7 mmol), magnesium oxide (MgO) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, and a hypoporous type strongly acidic cation exchange resin (Diaion TMRCP160M) (2.0 g, 200 wt% relative to the substrate) as a dehydration catalyst were placed in a pressure vessel. Methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0114] [Example A6] Glucose (1.0 g, 5.7 mmol), magnesium oxide (MgO) (1.0 g, 100 wt%) as an isomerization catalyst, and phosphate-activated carbon (1.0 g, 100 wt%) as a dehydration catalyst were placed in a pressure vessel. Methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added, and the vessel was sealed. The vessel was heated to 140°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0115] [Example A7] Glucose (1.0 g, 5.7 mmol), magnesium oxide (MgO) (1.0 g, 100 wt%) as an isomerization catalyst, and phosphate-modified silica gel (1.0 g, 100 wt%) as a dehydration catalyst were placed in a pressure vessel. Methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added, and the vessel was sealed. The vessel was heated to 140°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0116] [Comparative Example A1] Glucose (0.3 g, 1.7 mmol) and phosphoric acid (15 mg, 5 wt% relative to the substrate) as a catalyst were placed in a pressure vessel. Methyl isobutyl ketone (MIBK) (7 g) and water (3 g) were added, and the vessel was sealed. The vessel was heated to 140°C and heated with stirring for 4 hours. After 4 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0117] [Comparative example A2] Glucose (0.3g, 1.7 mmol) and phosphoric acid (15mg, applied to the substrate) as a catalyst. 5 wt% of the mixture was placed in a pressure vessel, and methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added and the vessel was sealed. The vessel was heated to 140°C and heated for 4 hours with stirring. After 4 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0118] [Comparative example A3] Glucose (1.0g, 5.7 mmol) and a hypoporous type strongly acidic cation exchange resin (Diaion) as a dehydration catalyst. TM 2.0 g of RCP160M (200 wt%) relative to the substrate and sodium chloride (NaCl) (1.0 g, 100 wt%) as an additive were placed in a pressure vessel, and 7 g of methyl isobutyl ketone (MIBK) and 3 g of water were added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0119] [Comparative example A4] Glucose (1.0 g, 5.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, a hyperporous type strongly acidic cation exchange resin (Diaion TMRCP160M) (2.0 g, 200 wt% relative to the substrate) as a dehydration catalyst, and sodium chloride (NaCl) (1.0 g, 100 wt% relative to the substrate) as an additive were placed in a pressure vessel, and dimethyl sulfoxide (DMSO) (10 g) was added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0120] [Comparative Example A5] Glucose (1.0 g, 5.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt%) relative to the substrate as an isomerization catalyst, and a hyperporous type strongly acidic cation exchange resin (Diaion) as a dehydration catalyst. TM 2.0 g of RCP160M (200 wt%) relative to the substrate was placed in a pressure vessel, and 10 g of dimethyl sulfoxide (DMSO) was added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0121] [Comparative example A6] Glucose (1.0 g, 5.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt%) as an isomerization catalyst, and porous strong acid cation exchange resin (Amberlyst® 15) (2.0 g, 200 wt%) as a dehydration catalyst were placed in a pressure vessel, and dimethyl sulfoxide (DMSO) (10 g) was added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0122] [Comparative example A7] Glucose (0.3g, 1.7 mmol) and aluminum oxide (A) as an isomerization catalyst. (1.0g, 100wt%) of l2O3, and a hypoporous type strongly acidic cation exchange resin (Diaion) as a dehydration catalyst. TM 2.0 g of RCP160M (200 wt%) relative to the substrate and 4.0 g of sodium chloride (NaCl) (400 wt%) as an additive were placed in a pressure vessel, and 7 g of methyltetrahydropyran (MTHP) and 3 g of water were added and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0123] [Comparative example A8] Glucose (0.1g, 0.5 mmol), aluminum oxide (Al2O3) (2.0g, 200 wt%) as an isomerization catalyst, and a hyperporous type strongly acidic cation exchange resin (Diaion) as a dehydration catalyst. TM 2.0 g of RCP160M (200 wt%) relative to the substrate, along with sodium chloride (NaCl) (4.0 g, 400 wt%) as an additive, were placed in a pressure vessel. Methyl isobutyl ketone (MIBK) (7 g), N-methylpyrrolidone (NMP) (2.4 g), and water (0.6 g) were added, and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0124] [Comparative example A9] Glucose (0.1g, 0.5 mmol), aluminum oxide (Al2O3) (2.0g, 200 wt%) as an isomerization catalyst, and a hyperporous type strongly acidic cation exchange resin (Diaion) as a dehydration catalyst. TM 2.0 g of RCP160M (200 wt%) relative to the substrate and sodium chloride (NaCl) (1.0 g, 100 wt%) as an additive were placed in a pressure vessel. Methyl isobutyl ketone (MIBK) (7 g), N-methylpyrrolidone (NMP) (2.4 g), and water (0.6 g) were added, and the vessel was sealed. The vessel was heated to 120°C and heated with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was collected by liquid-liquid extraction. Subsequently, the organic solvent was removed by distillation to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions and the selectivity and yield of 5-HMF are shown in Table 2.

[0125] [Table 2] *The catalyst and additive amounts in the table represent the mass ratio (wt%) to glucose (substrate).

[0126] As shown in Table 2, in the process of producing 5-HMF from glucose, Examples A1 to A7, which used a two-phase solvent and a mixed catalyst consisting of an isomerization catalyst and a dehydration catalyst, yielded 5-HMF in high yield and with high selectivity. On the other hand, Comparative Examples A1 to A9, which used conventional methods using only a two-phase solvent or only a mixed catalyst, showed lower yield and selectivity of 5-HMF compared to the examples, particularly lower selectivity. Furthermore, Comparative Examples A7 to A9 were investigated by adding 100 to 400 wt% of NaCl to the substrate, as in the prior art, but the yield and selectivity of 5-HMF were also low. As asserted in this technology, while the addition of a Na salt promotes the distribution of the product into the oil phase, it has a significant adverse effect on the isomerization catalyst and the dehydration catalyst, especially the dehydration catalyst (reduction in acid strength).

[0127] <<Example B>> The yield of the product was determined by adding trioxane as an internal standard to the reaction solution and quantifying the product using a nuclear magnetic resonance (NMR) spectrometer (JOEL-JNM-ECX400, JOEL Corporation). The measurement frequency was 400 MHz and the measurement solvent was deuterated dimethyl sulfoxide. The yield of FDCA was calculated using the following formula. Yield of HMF acetal in the acetalization process (%) = Moles of HMF acetal produced in the acetalization process / Moles of HMF used in the reaction in the acetalization process × 100 Yield of FFCA acetal in the oxidation step (%) = Moles of FFCA acetal produced in the oxidation step / Moles of HMF acetal used in the reaction in the oxidation step × 100 Yield of FFCA in the deprotection step (%) = Moles of FFCA produced in the deprotection step / Moles of FFCA acetal used in the reaction in the deprotection step × 100 Yield of FDCA in the second oxidation step (%) = Moles of FDCA produced in the second oxidation step / Moles of FFCA used in the reaction in the second oxidation step × 100 The total process yield of FDCA (%) = (Yield of HMF acetal in the acetalization process (%) / 100) × (Yield of FFCA acetal in the oxidation process (%) / 100) × (Yield of FFCA in the deprotection process (%) / 100) × (Yield of FDCA in the second oxidation process (%) / 100) × 100

[0128] [Example B1] <Acetalization process> HMF (10.0 g, 79.3 mmol), neopentyl glycol (12.4 g, 119.0 mmol) as a diol, and porous type strongly acidic cation exchange resin (Amberlist 15) (1.0 g, 10 wt% relative to the substrate) as a catalyst were added to toluene (40.0 g) as a solvent and stirred at 30°C for 1 hour. The reaction mixture was then cooled to room temperature, and the catalyst was separated by filtration. After washing with water, toluene was removed by distillation to obtain HMF acetal in 97% yield. The reaction conditions for the acetalization step and the yield of HMF acetal are shown in Table 3.

[0129] <First oxidation step> The obtained HMF acetal (4.0 g, 18.8 mmol), potassium carbonate (5.2 g, 37.6 mmol) as a base, and 5% palladium-supported carbon (Pd / C) (4.0 g, 100 wt% relative to the substrate) as a catalyst were added to water (16.0 g) as a solvent. Air was introduced to a pressure of 0.9 MPa, and the mixture was stirred at 80°C for 8 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Subsequently, the catalyst was separated by filtration to obtain an aqueous solution containing FFCA acetal represented by the following formula (4). The yield was 97%. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for the oxidation step and the yield of FFCA acetal are shown in Table 4. [ka]

[0130] <Deprotection process> The FFCA acetal (4.0 g, 17.7 mmol) obtained in the above example and a hypoplastic type strongly acidic cation exchange resin (Diaion TMRCP160M) (0.4 g, 10 wt% relative to the substrate) as a catalyst were added to water (16.0 g) as a solvent and stirred at 60°C for 1 hour. The reaction mixture was then cooled to room temperature, and the catalyst was separated by filtration. Subsequently, it was washed with ethyl acetate to obtain FFCA in 96% yield. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for the deprotection step and the yield of FFCA are shown in Table 5.

[0131] <Second oxidation step> The obtained FFCA (2.4g, 17.0 mmol), potassium carbonate (4.7g, 34.0 mmol) as a base, and 5% palladium-supported carbon (Pd / C) (2.4g, 100 wt% relative to the substrate) as a catalyst were added to water (9.6g) as a solvent, and air was removed. The reaction mixture was introduced to a pressure of 0.9 MPa and stirred at 80°C for 8 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Next, the catalyst was separated by filtration, sulfuric acid was added to the resulting filtrate, and the precipitated material was collected by filtration. The resulting solid was washed with water to obtain FDCA in 96% yield. The overall yield of FDCA throughout the entire process was 87%. The reaction conditions for the second oxidation step and the yield of FDCA are shown in Table 6.

[0132] [Example B2] <Acetalization process> HMF acetals were obtained in 97% yield using the same method as in Example B1, except that the amounts of HMF (40.0 g, 317.2 mmol), neopentyl glycol (49.6 g, 475.8 mmol), porous type strongly acidic cation exchange resin (Amberlist 15) (4.0 g, 10 wt% relative to the substrate), and toluene (60.0 g) were changed. The reaction conditions for the acetalization step and the yield of HMF acetals are shown in Table 3.

[0133] <First oxidation step> FFCA acetal was obtained in 97% yield using the same method as in Example B1, except that the amounts of HMF acetal (8.0 g, 37.7 mmol), potassium carbonate (10.4 g, 75.4 mmol), 5% palladium-supported carbon (Pd / C) (0.8 g, 10 wt% relative to the substrate), and water (12.0 g) were changed. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for this oxidation step and the yield of FFCA acetal are shown in Table 4.

[0134] <Deprotection process> FFCA was obtained in 95% yield using the same method as in Example B1, except that the amount of water was changed to 6.0 g. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for the deprotection step and the yield of FFCA are shown in Table 53.

[0135] <Second oxidation step> FDCA was obtained in 97% yield using the same method as in Example B1, except that the amounts of FFCA (1.2 g, 8.6 mmol), potassium carbonate (2.4 g, 17.2 mmol), 5% palladium-supported carbon (Pd / C) (0.12 g, 10 wt% relative to the substrate), and water (1.8 g) were changed. The overall yield of FDCA was 87%. The reaction conditions for the second oxidation step and the yield of FDCA are shown in Table 6.

[0136] [Example B3] <Acetalization process> HMF acetal was obtained in 96% yield using the same method as in Example B2, except that the amount of neopentyl glycol was changed to 39.6 g and 380.6 mmol. The reaction conditions for the acetalization step and the yield of HMF acetal are shown in Table 3.

[0137] <First oxidation step> FFCA acetal was obtained in 97% yield by the same method as in Example B2, except that 5% platinum-supported carbon (Pt / C) (0.8 g, 10 wt% relative to the substrate) was used as a catalyst. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for this oxidation step and the yield of FFCA acetal are shown in Table 4.

[0138] <Deprotection process> FFCA was obtained in 96% yield using the same method as in Example B2, except that the reaction time was changed to 2 hours. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for the deprotection step and the yield of FFCA are shown in Table 5.

[0139] <Second oxidation step> FDCA was obtained in 98% yield using the same method as in Reference Example 2, except that 5% platinum-supported carbon (Pt / C) (0.1g, 10wt% relative to the substrate) was used as a catalyst. The overall yield of FDCA was 88%. The reaction conditions for the second oxidation step and the yield of FDCA are shown in Table 6.

[0140] [Comparison reference example B1] HMF (0.3 g, 2.4 mmol) and 5% platinum-supported carbon (Pt / C) (0.03 g, 10 wt% relative to the substrate) as a catalyst were added to water (2.7 g) as a solvent. Air was introduced to a pressure of 0.9 MPa, and the mixture was stirred at 80°C for 16 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Subsequently, the catalyst was separated by filtration, sulfuric acid was poured into the resulting filtrate, and the precipitated precipitate was collected by filtration. The obtained solid was washed with water to obtain FDCA in a yield of 22%. The reaction conditions and the yield of FDCA are shown in Table 7.

[0141] [Comparison reference example B2] FDCA was obtained in 45% yield by the same method as in comparative reference example B1, except that HMF (1.2 g, 9.6 mmol), 5% platinum-supported carbon (Pt / C) (0.12 g, 10 wt% relative to the substrate) and potassium carbonate (2.65 g, 19.2 mmol) were added as catalysts to water (1.8 g) as a solvent. The reaction conditions and FDCA yield are shown in Table 7.

[0142] [Table 3]

[0143] [Table 4]

[0144] [Table 5]

[0145] [Table 6]

[0146] [Table 7]

[0147] As shown in Table 3, Examples B1 to B3, which included an oxidation step in which HMF acetal was contacted with an oxidation catalyst, yielded FFCA acetal in high yield. Furthermore, as shown in Table 4, Examples B1 to B3, which included a deprotection step in which FFCA acetal was deprotected, yielded FFCA in high yield. Also, as shown in Tables 5 and 6, Examples B1 to B3, using the obtained FFCA acetal, yielded FDCA in high yield. Finally, as shown in Table 6, Examples B1 to B3, which included a second oxidation step in which FFCA was contacted with an oxidation catalyst, yielded FDCA in high yield. On the other hand, as shown in Table 7, comparative reference examples B1-B2, which used a conventional method for producing FDCA by direct oxidation of HMF, showed a lower FDCA yield compared to examples B1-B3. Furthermore, FDCA ester can be obtained by oxidative esterification of the FFCA obtained in the deprotection step of this embodiment in the second oxidation step.

[0148] <<Example C>> [Example C1] <Process (i): Acetalization process> HMF (10.0 g, 79.3 mmol), neopentyl glycol (12.4 g, 119.0 mmol) as a diol, and porous type strongly acidic cation exchange resin (Amberlist 15) (1.0 g, 10 wt% relative to the substrate) as a catalyst were added to toluene (40.0 g) as a solvent and stirred at 30°C for 1 hour. The reaction mixture was then cooled to room temperature, and the catalyst was separated by filtration. After washing with water, toluene was removed by distillation to obtain HMF acetal in 97% yield. The reaction conditions for step (i) are shown in Table 8.

[0149] <Step (ii): First oxidation step> The obtained HMF acetal (4.0 g, 18.8 mmol), potassium carbonate (5.2 g, 37.6 mmol) as a base, and 5% palladium-supported carbon (Pd / C) (4.0 g, 100 wt% relative to the substrate) as a catalyst were added to water (16.0 g) as a solvent. Air was introduced at 0.9 MPa, and the mixture was stirred at 80°C for 8 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Subsequently, the catalyst was separated by filtration to obtain FFCA acetal in 97% yield. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0150] <Step (iii): Deprotection step> The obtained FFCA acetal (4.0 g, 17.7 mmol) and a hypo-porous type strongly acidic cation exchange resin (Diaion) as a catalyst were used. TM RCP160M) (0.4 g, 10 wt% relative to the substrate) was added to water (16.0 g) as a solvent and stirred at 60°C for 1 hour. The reaction mixture was then cooled to room temperature, and the catalyst was separated by filtration. Subsequently, it was washed with ethyl acetate to obtain FFCA in 96% yield. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for step (iii) are shown in Table 10.

[0151] <Step (iv): Second oxidation step> The obtained FFCA (2.4 g, 17.0 mmol), potassium carbonate (4.7 g, 34.0 mmol) as a base, and 5% palladium-supported carbon (Pd / C) (2.4 g, 100 wt% relative to the substrate) as a catalyst were added to water (9.6 g) as a solvent. Air was introduced at 0.9 MPa, and the mixture was stirred at 80°C for 8 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Subsequently, the catalyst was separated by filtration, sulfuric acid was poured into the resulting filtrate, and the precipitated precipitate was collected by filtration. The obtained solid was washed with water to obtain FDCA in 96% yield. The overall yield of FDCA throughout the entire process was 87%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0152] [Example C2] <Process (i): Acetal Process> HMF acetal was obtained in 97% yield by the same method as in Example 1, except that the amount of neopentyl glycol was 9.9 g, or 95.2 mmol. The reaction conditions are shown in Table 8. <Step (ii): First oxidation step> FFCA acetal was obtained in 98% yield by the same method as in Example 1, except that 5% platinum-supported carbon (Pt / C) (4.0 g, 100 wt% relative to the substrate) was used as a catalyst. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0153] <Step (iii): Deprotection step> FFCA was obtained in 96% yield using the same method as in Example 1. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> FDCA was obtained in 97% yield by the same method as in Example 1, except that 5% platinum-supported carbon (Pt / C) (2.4 g, 100 wt% relative to the substrate) was used as a catalyst. The overall yield of FDCA was 89%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0154] [Example C3] <Process (i): Acetalization process> HMF (40.0 g, 317.2 mmol) was added to propanediol (60.0 g, 788.5 mmol) as a solvent, and the mixture was stirred at 80°C for 12 hours. Propanediol also acts as a diol for acetalization. During this process, a zeolite membrane ZX2 (CHA type, SiO2 / Al2O3=6~8, vacuum 12 Pa) was immersed in the reaction solution, and the reaction solution was stirred while dehydrating it. After that, the reaction solution was cooled to room temperature, and the propanediol was removed by distillation to obtain HMF acetal in 96% yield. The reaction conditions for step (i) are shown in Table 8. <Step (ii): First oxidation step> The obtained HMF acetal (8.0 g, 37.7 mmol), potassium carbonate (10.4 g, 75.4 mmol) as a base, 2% gold-supported hydroxyapatite (Au / HAP) (0.8 g, 10 wt% relative to the substrate) as a catalyst, and water (12.0 g) as a solvent. In addition, air was introduced at 0.9 MPa and the mixture was stirred at 80°C for 8 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Subsequently, the catalyst was separated by filtration, yielding FFCA acetal in 95% yield. No decomposition of propanediol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0155] <Step (iii): Deprotection step> FFCA was obtained in 96% yield using the same method as in Example 1, except that the amount of water was changed to 6.0 g and the reaction time to 2 hours. No decomposition of propanediol was observed in this step. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> The obtained FFCA (1.2 g, 8.6 mmol), potassium carbonate (2.4 g, 17.2 mmol) as a base, and 2% gold-supported hydroxyapatite (Au / HAP) (0.12 g, 10 wt% relative to the substrate) as a catalyst were added to water (1.8 g) as a solvent. Air was introduced at 0.9 MPa, and the mixture was stirred at 80°C for 8 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Subsequently, the catalyst was separated by filtration, sulfuric acid was poured into the resulting filtrate, and the precipitated precipitate was collected by filtration. The obtained solid was washed with water to obtain FDCA in 91% yield. The overall yield of FDCA throughout the entire process was 80%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0156] [Example C4] <Process (i): Acetalization process> HMF (40.0 g, 317.2 mmol), neopentyl glycol (49.6 g, 475.8 mmol) as a diol, and porous type strongly acidic cation exchange resin (Amberlist 15) (4.0 g, 10 wt% relative to the substrate) as a catalyst were added to toluene (60.0 g) as a solvent and stirred at 30°C for 1 hour. The reaction mixture was then cooled to room temperature, and the catalyst was separated by filtration. After washing with water, toluene was removed by distillation to obtain HMF acetal in 97% yield. The reaction conditions for step (i) are shown in Table 8. <Step (ii): First oxidation step> FFCA acetal was obtained in 97% yield by the same method as in Example 3, except that 5% palladium-supported carbon (Pd / C) (0.8 g, 10 wt% relative to the substrate) was used as a catalyst. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0157] <Step (iii): Deprotection step> FFCA was obtained in 95% yield using the same method as in Example 1, except that the amount of water was changed to 6.0 g. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> FDCA was obtained in 97% yield by the same method as in Example 3, except that 5% palladium-supported carbon (Pd / C) (0.12 g, 10 wt% relative to the substrate) was used as a catalyst. The overall yield of FDCA was 87%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0158] [Example C5] <Process (i): Acetalization process> HMF acetal was obtained in 96% yield using the same method as in Example 4, except that the amount of neopentyl glycol was changed to 39.6 g and 380.6 mmol. The reaction conditions for step (i) are shown in Table 8. <Step (ii): First oxidation step> As a catalyst, 5% platinum-supported carbon (Pt / C) (0.8g, 10 wt relative to the substrate) FFCA acetal was obtained in 97% yield using the same method as in Example 3, except that %) was used. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0159] <Step (iii): Deprotection step> FFCA was obtained in 96% yield using the same method as in Example 1, except that the amount of water was changed to 6.0 g and the reaction time to 2 hours. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> FDCA was obtained in 98% yield by the same method as in Example 3, except that 5% platinum-supported carbon (Pt / C) (0.1 g, 10 wt% relative to the substrate) was used as a catalyst. The overall yield of FDCA was 88%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0160] [Comparative Example C1] HMF (0.3 g, 2.4 mmol) and 5% platinum-supported carbon (Pt / C) (0.03 g, 10 wt% relative to the substrate) as a catalyst were added to water (2.7 g) as a solvent. Air was introduced at 0.9 MPa, and the mixture was stirred at 80°C for 16 hours. The reaction mixture was then cooled to room temperature, and the reaction vessel was depressurized. Subsequently, the catalyst was separated by filtration, and sulfuric acid was poured into the resulting filtrate. The precipitated material was collected by filtration. The obtained solid was washed with water to obtain FDCA in 22% yield. The reaction conditions and FDCA yield are shown in Table 12. [Comparative Example C2] FDCA was obtained in 57% yield by the same method as in Comparative Example C1, except that HMF (0.9 g, 7.2 mmol), 5% platinum-supported carbon (Pt / C) (0.09 g, 10 wt% relative to the substrate) and potassium carbonate (2.0 g, 14.4 mmol) were added as catalysts to water (2.1 g) as a solvent. The reaction conditions and FDCA yield are shown in Table 12. [Comparative Example C3] HMF (1.2 g, 9.6 mmol), 5% platinum supported carbon (Pt / C) (0.12 g, 10 wt% based on the substrate) as a catalyst, and potassium carbonate (2.65 g, 19.2 mmol) were added to water (1.8 g) as a solvent, and FDCA was obtained in a yield of 45% in the same manner as in Comparative Example C1 except for this. The reaction conditions and the yield of FDCA are shown in Table 12.

[0161]

Table 8

[0162]

Table 9

[0163]

Table 10

[0164]

Table 11

[0165]

Table 12

[0166] As shown in Table 11, in the process of producing FDCA from HMF, in Examples C1 to C5 using the method having steps (i) to (v), FDCA was obtained in a high yield. On the other hand, as shown in Table 12, in Comparative Examples C1 to C3 using the conventional method for producing FDCA by direct oxidation of HMF, the FDCA yield was lower as compared with Examples C1 to C5. v), the FDCA was obtained in a high yield. On the other hand, as shown in Table 12, in Comparative Examples C1 to C3 using the conventional method for producing FDCA by direct oxidation of HMF, the FDCA yield was lower as compared with Examples C1 to C5.< / vi> < / v> < / iv> < / iii> < / ii>

Claims

1. A method for producing a furan derivative having an acetal group and a carbonyl group, comprising an oxidation step of contacting hydroxymethylfurfural acetal with an oxidation catalyst.

2. The manufacturing method according to claim 1, wherein the furan derivative is a compound represented by formula (1). 【Chemistry 1】 (In formula (1), Z is a hydrogen atom or a hydroxyl group, and R ２ and R ３ (These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.)

3. The production method according to claim 1 or 2, wherein the concentration of the furan derivative in the total compounds having a furan skeleton in the product after the oxidation step is 70 mol% or more.

4. The manufacturing method according to claim 1 or 2, wherein the oxidation catalyst is a metal catalyst.

5. A furan derivative represented by formula (1). 【Chemistry 2】 (In formula (1), Z is a hydrogen atom or a hydroxyl group, and R ２ and R ３ (These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.)

6. A solution comprising the furan derivative described in claim 5, wherein the concentration of the furan derivative in the total compounds having a furan skeleton is 70 mol% or more.

7. The solution according to claim 6, wherein the furan derivative is a compound represented by formula (2). 【Transformation 3】 (In formula (2), R ２ and R ３ (These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.)

8. A method for producing a furan derivative, comprising a deprotection step of synthesizing a furan derivative by deprotecting a formylfuran acetal or its ester, A method for producing the furan derivative, wherein the furan derivative is one or more selected from the group consisting of formylfuranic acid and its esters.

9. The method for producing the product according to claim 8, wherein the formylfuran acetal or ester thereof is a compound represented by formula (3). 【Chemistry 4】 (In formula (3), X, R ４ and R ５ (These are independently selected from a hydrogen atom, a C1-C6 alkyl group, and a C6-C12 aryl group which may have an alkyl substituent.)

10. The production method according to claim 8 or 9, wherein in the product after the deprotection step, the concentration of formylfurancarboxylic acid and its esters in the total compounds having a furan skeleton is 70 mol% or more.

11. The manufacturing method according to claim 8 or 9, further comprising a recovery step of recovering a diol from the reaction solution after the deprotection step.

12. The manufacturing method according to claim 11, wherein the diol is a diol having 2 to 10 carbon atoms.

13. A solution containing compounds having a furan skeleton, wherein the concentration of formylfuran carboxylic acid and its esters in the total compounds having a furan skeleton is 70 mol% or more.

14. A method for producing a furan carboxylic acid or its ester, comprising an oxidation step of contacting a composition containing a furan derivative with an oxidation catalyst, The furan derivative is one or more selected from the group consisting of diformylfuran, formylfuran carboxylic acid, and its esters. A method for producing the furan derivative, wherein the concentration of the furan derivative in the total compounds having a furan skeleton contained in the composition containing the furan derivative is 70% by mass or more.

15. The manufacturing method according to claim 14, wherein the oxidation catalyst is a metal catalyst.

16. A method for producing frangic acid or frangic acid ester from hydroxymethylfurfural, comprising the following manufacturing steps (i) to (iv). (i) An acetalization step to synthesize hydroxymethylfurfural acetal by acetalizing hydroxymethylfurfural. (ii) A first oxidation step in which hydroxymethylfurfural acetal is oxidized to synthesize formylfuran acetal or its ester. (iii) Deprotecting formylfuran acetal or its ester A deprotection step for synthesizing refranic acid or its ester. (iv) A second oxidation step in which formylfuran carboxylic acid or its ester is oxidized.

17. The method for producing a frangic acid or frangic acid ester according to claim 16, wherein the formylfuran acetal or ester thereof is a compound represented by formula (3). 【Transformation 5】 (In formula (3), X, R ４ and R ５ are each independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent.)

18. A method for producing a frangic acid or frangic acid ester according to claim 16 or 17, wherein in step (i), an organic solvent selected from toluene and methyltetrahydropyran is used.

19. A method for producing a frangic acid or frangic acid ester according to claim 16 or 17, further comprising a recovery step of recovering a diol from the reaction solution after step (iii) above.

20. The method for producing a frangic acid or frangic acid ester according to claim 19, wherein the diol is a diol having 2 to 10 carbon atoms.

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