Method for producing 2,5-diformylfuran

Abstract

To provide a method for producing DFF that is capable of easily producing DFF in a one-pot manner from saccharides without the need for a specific catalyst such as a vanadium compound.SOLUTION: A method for producing 2,5-diformylfuran comprising a heating step of heating saccharides in the presence of a sulfoxide compound and a halide salt to react the saccharides, thereby generating 2,5-diformylfuran.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing 2,5-diformylfuran. [Background technology]

[0002] 2,5-Diformylfuran (hereinafter also referred to as DFF) is useful as a raw material or intermediate for resins, pharmaceuticals, fragrances, etc. DFF is a versatile intermediate that can be produced from naturally occurring sugars derived from biomass.

[0003] Patent Document 1 discloses a method for synthesizing 2,5-diformylfuran, which includes a hydrothermal step in which a raw material containing a biomass-derived carbohydrate is hydrothermally treated in the presence of one or more salts of an alkali metal salt and an alkaline earth metal salt using a mixed liquid of an organic liquid and water as a medium to obtain a reaction liquid containing 5-hydroxymethyl-2-furfural; a water removal step in which water is removed from the organic liquid layer of the reaction liquid to obtain a crude product containing 5-hydroxymethyl-2-furfural; and an oxidation step in which 5-hydroxymethyl-2-furfural in the crude product is oxidized to obtain 2,5-diformylfuran.

[0004] Patent Document 2 states: a) combining a carbohydrate source with a solvent; b) heating the reaction mixture of step (a) at a temperature sufficient to produce 2,5-hydroxymethylfurfural; c) adding an oxidizing agent and a catalytic amount of a vanadium compound to the reaction mixture of step (b). , and d) heating the reaction mixture of step (c) at a temperature sufficient to produce 2,5-diformylfuran. wherein no additional solvent is added after steps (b), (c), or (d). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-143046 [Patent Document 2] Special Publication No. 2005-506984 Summary of the Invention [Problem to be solved by the invention]

[0006] In the synthesis method described in Patent Document 1, saccharides are dehydrated to produce 5-hydroxymethyl-2-furfural (hereinafter also referred to as HMF), the crude product containing HMF is isolated, and then the HMF is oxidized using a solvent different from that used in the dehydration reaction to produce DFF. This requires two complicated steps, one for producing HMF and the other for producing DFF. Furthermore, after the HMF production step, treatments such as isolating the crude product containing HMF and replacing the solvent are required, which requires time and money. In the production method described in Patent Document 2, a step of producing HMF by dehydrating a carbohydrate source and a step of producing DFF by oxidizing HMF are carried out in one pot. However, in the production method described in Patent Document 2, DFF is produced using an expensive vanadium catalyst, and as described in the examples of Patent Document 2, a special vanadium catalyst needs to be prepared. An object of the present invention is to provide a method for producing DFF, which enables DFF to be easily produced from sugars in one pot without using a special catalyst such as a vanadium compound. [Means for solving the problem]

[0007] As a result of intensive research to solve the above problems, the present inventors have conceived the following invention and found that the problems can be solved. That is, the present invention is as follows.

[0008] [1] A method for producing 2,5-diformylfuran, comprising a heating step of heating a sugar in the presence of a sulfoxide compound and a halide salt to react the sugar to produce 2,5-diformylfuran. [2] The method for producing 2,5-diformylfuran according to [1] above, wherein the halide salt is a salt of at least one of an alkali metal ion and an alkaline earth metal ion with a halide ion. [3] The method for producing 2,5-diformylfuran according to [1] or [2] above, wherein in the heating step, the sugars are further heated in the presence of an acid catalyst to react with each other to produce 2,5-diformylfuran. [4] The method for producing 2,5-diformylfuran according to [3] above, wherein the acid catalyst is one or more selected from the group consisting of Lewis acids and Bronsted acids. [5] The method for producing 2,5-diformylfuran according to any one of the above [1] to [4], wherein the heating temperature in the heating step is 80 to 180°C. [6] The method for producing 2,5-diformylfuran according to any one of the above [1] to [5], wherein the heating step comprises a first heating step and a second heating step at a temperature higher than that of the first heating step. [7] The method for producing 2,5-diformylfuran according to [6] above, wherein the first heating step is further carried out in the presence of a first acid catalyst. [8] The method for producing 2,5-diformylfuran according to [7] above, wherein a second acid catalyst is added during the period from the middle of the first heating step to the middle of the second heating step. [9] The method for producing 2,5-diformylfuran according to any one of the above [1] to [8], wherein the saccharide is a saccharide having at least one skeleton selected from a fructose skeleton and a glucose skeleton. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described below based on an example of an embodiment, but the embodiment shown below is merely an example for embodying the technical concept of the present invention, and the present invention is not limited to the following description. In this specification, preferred embodiments are shown, but a combination of two or more of the individual preferred embodiments is also a preferred embodiment. When there are several numerical ranges for matters shown as numerical ranges, the lower limit and upper limit can be selectively combined to form a preferred embodiment. Furthermore, when a numerical range is described as "XX to YY," it means "XX or more and YY or less." As used herein, "one-pot" means that no HMF isolation procedure is performed until DFF is produced by reacting saccharides. Note that, as used herein, even when HMF isolation is performed after DFF production, this also falls under the category of one-pot.

[0010] The method for producing 2,5-diformylfuran according to the present embodiment includes a heating step of heating sugars in the presence of a sulfoxide compound and a halide salt to react the sugars and produce 2,5-diformylfuran. According to the method for producing 2,5-diformylfuran of this embodiment, DFF can be easily produced from sugars in one pot without using a special catalyst such as a vanadium compound. By using a sulfoxide compound and a halide salt, the halide ions enhance the activity of the sulfoxide compound, and not only does it produce HMF through the dehydration reaction of sugars, but it also produces DFF through the oxidation reaction of HMF. After the heating step, an extraction step, a washing step, a dehydration step, and a crystal recovery and purification step, which will be described later, may be carried out.

[0011] [Heating process] The heating step is a step in which saccharides are heated in the presence of a sulfoxide compound and a halide salt to react with each other to produce 2,5-diformylfuran. According to the method for producing 2,5-diformylfuran according to the present embodiment, it is not necessary to carry out an operation for isolating HMF during the heating step, and therefore DFF can be produced easily. Furthermore, in the method for producing 2,5-diformylfuran according to the present embodiment, the sulfoxide compound is not replaced with another solvent during the heating step, which allows for easy production of DFF. Furthermore, in the method for producing 2,5-diformylfuran according to this embodiment, a solvent other than the sulfoxide compound may or may not be added during the heating step, but from the viewpoint of producing DFF more easily, it is preferable not to add the solvent. According to the method for producing 2,5-diformylfuran according to this embodiment, DFF can be produced without adding the solvent.

[0012] <Sugars> The sugars may be naturally occurring or artificially synthesized, or may be a mixture of two or more of these. Specific examples of sugars include monosaccharides, disaccharides, oligosaccharides, polysaccharides, and the like. Examples of the monosaccharides include fructose, glucose, galactose, mannose, and sorbose. Examples of the disaccharides include sucrose, maltose, cellobiose, and lactose. Examples of the oligosaccharides include any combination of monosaccharides. Examples of the polysaccharides include any combination of monosaccharides, starch, cellulose, and inulin. In addition, mixtures containing the components such as starch, sugar solutions derived from sugar cane, sugar beet, soybeans, etc., as well as their refined intermediates and refined by-products, such as high fructose corn syrup, refined sugar, raw sugar, blackstrap molasses, invert sugar, and isomerized sugar, can also be used as sugars.

[0013] As the sugar, a sugar having at least one selected from a fructose skeleton and a glucose skeleton is preferred from the viewpoints of conversion efficiency to HMF and side reaction products. Furthermore, from the viewpoint of economical and efficient production of DFF, the sugar is preferably a sugar raw material containing fructose. Examples of preferred sugar raw materials containing fructose include fructose, disaccharides obtained by combining fructose with any monosaccharide, oligosaccharides obtained by combining fructose with any monosaccharide, polysaccharides obtained by combining fructose with any monosaccharide, high fructose corn syrup, its purification intermediates and by-products, soybean molasses, sugar cane or sugar beet-derived molasses and refined sugar obtained from the molasses, raw sugar, blackstrap molasses, invert sugar, and inulin. Among these, from the viewpoint of economical and efficient production of HMF oxide, a mixture of glucose and fructose, refined sugar, raw sugar, blackstrap molasses, fructose, sucrose, or inulin is more preferred, and at least one selected from fructose, glucose, and oligosaccharides is even more preferred. When using a sugar raw material that does not contain fructose or has a low fructose content, the fructose content may be increased by pretreatment in advance. Specific examples of the pretreatment include isomerization treatment or hydrolysis treatment using enzymes or chemicals, acid treatment, base treatment, etc. Among these, from the viewpoints of productivity and economy, pretreatment using enzymes is preferred, and pretreatment including isomerization enzyme treatment is preferred.

[0014] <Sulfoxide compounds> Sulfoxide compounds are reaction solvents that dissolve sugars and promote their reactions. When used in combination with halide salts, sulfoxide compounds not only promote the production of HMF through the dehydration reaction of sugars, but also significantly promote the production of DFF through the oxidation reaction of HMF. There are no particular limitations on the sulfoxide compound (RS(=O)-R'), but from the viewpoint of easily producing DFF from saccharides in one pot, a compound in which the substituents R and R' bonded to the sulfinyl group are aliphatic hydrocarbon groups is preferred. From the viewpoint of easily producing DFF from saccharides in one pot, the number of carbon atoms in the substituents R and R', which are aliphatic hydrocarbon groups, is each independently preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3. Among these, preferred are dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, etc., and more preferred is dimethyl sulfoxide.

[0015] The amount of the sulfoxide compound is preferably 400 to 10,000 parts by mass per 100 parts by mass of the sugars. An amount of 400 parts by mass or more can sufficiently dissolve the sugars, promoting not only the production of HMF by the dehydration reaction of the sugars but also the production of DFF by the oxidation reaction of HMF. An amount of 10,000 parts by mass or less can improve productivity, such as yield, and economic efficiency. From this perspective, the amount of the sulfoxide compound is more preferably 600 to 5,000 parts by mass, and even more preferably 800 to 2,000 parts by mass per 100 parts by mass of the sugars.

[0016] <Halide salts> The halide salt is not particularly limited, but from the viewpoint of easily producing DFF from saccharides in one pot, it is preferably a salt of at least one of an alkali metal ion and an alkaline earth metal ion with a halide ion, and more preferably a salt of an alkali metal ion with a halide ion.

[0017] As the alkali metal, from the viewpoint of easily producing DFF from saccharides in one pot, preferably, one or more selected from the group consisting of lithium, sodium, and potassium, more preferably, one or more selected from the group consisting of sodium and potassium, and even more preferably, sodium. From the viewpoint of easily producing DFF from sugars in one pot, the alkaline earth metal is preferably one or more selected from the group consisting of beryllium, magnesium, calcium, strontium, and barium, more preferably one or more selected from the group consisting of magnesium and calcium, and even more preferably calcium.

[0018] From the viewpoint of easily producing DFF from saccharides in one pot, the halogen element is preferably one or more selected from the group consisting of fluorine, chlorine, bromine, and iodine, more preferably one or more selected from the group consisting of chlorine and bromine, and even more preferably bromine. It is believed that the combined use of the halide salt with a sulfoxide compound, preferably the combined use of a salt of at least one of an alkali metal ion and an alkaline earth metal ion with a halide ion with a sulfoxide compound, not only promotes the production of HMF through the dehydration reaction of sugars, but also significantly promotes the production of DFF through the oxidation reaction of HMF.

[0019] The halide salt is preferably sodium halide (sodium fluoride, sodium chloride, sodium bromide, sodium iodide), potassium halide (potassium fluoride, potassium chloride, potassium bromide, potassium iodide), calcium halide (calcium fluoride, calcium chloride, calcium bromide, calcium iodide), more preferably sodium halide (sodium fluoride, sodium chloride, sodium bromide, sodium iodide), and even more preferably sodium bromide.

[0020] The amount of the halide salt to be added is preferably 0.01 to 25 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the sulfoxide compound, from the viewpoint of significantly promoting the production of DFF by the oxidation reaction of HMF.

[0021] <Acid catalyst> In the heating step, the sugars may be further heated in the presence of an acid catalyst to react with the sugars to produce 2,5-diformylfuran, which further promotes the reaction of producing HMF from the sugars and enables efficient conversion to DFF. The acid catalyst is preferably one or more selected from the group consisting of Lewis acids and Bronsted acids, from the viewpoint of promoting the reaction of producing DFF from sugars via HMF. In this specification, the term "acid catalyst" does not include salts of at least one of alkali metal ions and alkaline earth metal ions with halide ions. In addition, in this specification, a component that corresponds to both a Lewis acid and a Bronsted acid is considered to be a Bronsted acid.

[0022] The Lewis acid is not particularly limited, and examples thereof include halides of metals other than alkali metals and alkaline earth metals or hydrates thereof, and organometallic compounds. From the viewpoint of reactivity, halides of metals other than alkali metals and alkaline earth metals or hydrates thereof are preferred, and from the viewpoints of versatility, economy, and ease of availability, hydrates of halides of metals other than alkali metals and alkaline earth metals are more preferred. Examples of halides of metals other than alkali metals and alkaline earth metals include iron halides (iron chloride, iron bromide, iron fluoride, etc.), aluminum halides (aluminum chloride, aluminum bromide, aluminum fluoride, etc.), and boron halides (boron chloride, boron bromide, boron fluoride, etc.), of which iron halides are preferred, and iron chloride is more preferred. The organometallic compound is not particularly limited, but examples thereof include triphenylborane, triphenylaluminum, tris(pentafluorophenyl)borane, and tris(pentafluorophenyl)aluminum. The amount of Lewis acid added is preferably 0.001 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and even more preferably 0.25 to 1.5 parts by mass, relative to 100 parts by mass of the sulfoxide compound, from the viewpoint of not only significantly promoting the production of HMF through the dehydration reaction of saccharides but also promoting the production of DFF through the oxidation reaction of HMF.

[0023] The Bronsted acid component may be an inorganic acid or an organic acid, but from the viewpoint of reactivity and ease of use, an organic acid is more preferable. Examples of inorganic acids include hydrochloric acid, nitric acid, nitrous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, sulfuric acid, sulfurous acid, boric acid, hydrofluoric acid, and fluorosulfonic acid. Examples of organic acids include carboxylic acids and sulfonic acids, with carboxylic acids being more preferred from the viewpoints of versatility and economy. A solid acid catalyst such as an ion exchange resin may also be used.

[0024] Examples of carboxylic acids include monocarboxylic acids having 1 to 18 carbon atoms (formic acid, acetic acid, propionic acid, etc.), dicarboxylic acids having 2 to 18 carbon atoms (oxalic acid, malonic acid, succinic acid, glutaric acid, etc.), trivalent or higher polycarboxylic acids having 3 to 18 carbon atoms (aconitic acid, etc.), and aromatic carboxylic acids (benzoic acid, phthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.). Of these, from the viewpoints of economy and availability, monocarboxylic acids having 1 to 18 carbon atoms or dicarboxylic acids having 2 to 18 carbon atoms are preferred, and formic acid or oxalic acid is more preferred. The carboxylic acid may be either a hydrate or not a hydrate. Examples of sulfonic acids include alkylsulfonic acids having 1 to 18 carbon atoms (e.g., methanesulfonic acid), sulfonic acids in which the alkyl chain of the alkylsulfonic acid is partially substituted (e.g., trifluoromethanesulfonic acid, taurine), and aromatic sulfonic acids (e.g., benzenesulfonic acid, toluenesulfonic acid, dodecylbenzenesulfonic acid). The amount of Bronsted acid added is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass, relative to 100 parts by mass of the sulfoxide compound, from the viewpoint of not only promoting the production of HMF through the dehydration reaction of saccharides but also significantly promoting the production of DFF through the oxidation reaction of HMF.

[0025] <Other ingredients> In the heating step, components other than the above-mentioned components may be added, or components other than the above-mentioned components may not be added, but from the viewpoint of easily producing DFF, it is preferable not to add components other than the above-mentioned components. For example, in the heating step, a metal catalyst such as manganese dioxide or a vanadium compound, or an oxidizing agent such as oxygen or a peroxide may or may not be added, but from the viewpoint of easily producing 2,5-diformylfuran, it is preferable not to add them. According to the method for producing 2,5-diformylfuran of this embodiment, DFF can be easily produced from saccharides without adding a catalyst or an oxidizing agent. For example, in the heating step, an oxygen-containing gas or gas mixture such as air (hereinafter sometimes referred to as air or the like) may or may not be supplied to the reaction system, but it is preferable not to supply it. According to the method for producing 2,5-diformylfuran of this embodiment, DFF can be easily produced from saccharides without adding air or the like.

[0026] <Heating conditions> The heating temperature in the heating step is preferably 80 to 180°C. At a temperature of 80°C or higher, the reaction from sugars to DFF is promoted. At a temperature of 180°C or lower, the production of by-products such as humic substances formed by condensation of furan compounds such as HMF and DFF is suppressed. From this viewpoint, the heating temperature in the heating step is more preferably 100 to 170°C, even more preferably 110 to 160°C, and even more preferably 120 to 150°C. The heating time in the heating step is preferably 0.5 to 20 hours. If it is 0.5 hours or more, the reaction from sugars to DFF is promoted. If it is 20 hours or less, the production of by-products such as humic substances formed by condensation of furan compounds such as HMF and DFF is suppressed. From this viewpoint, the heating temperature in the heating step is more preferably 1 to 15 hours, even more preferably 3 to 7 hours, and even more preferably 3 to 5 hours.

[0027] The heating atmosphere may be an inert gas atmosphere such as nitrogen gas, but from the viewpoint of easily producing the DFF, an air atmosphere is preferable. Furthermore, since this production method uses a sulfoxide compound as both a solvent and an oxidizing agent, other oxidizing agents or oxygen gas are not required. Therefore, gas such as air may or may not be bubbled, but from the viewpoint of easily producing DFF, bubbling is not necessary. According to the DFF production method of this embodiment, DFF can be produced with a high yield even without bubbling. The heating step may be carried out under increased pressure, reduced pressure, or normal pressure, but is preferably carried out under normal pressure from the viewpoint of easily producing DFF.

[0028] <First heating step> The heating step may include a first heating step and a second heating step at a temperature higher than that of the first heating step, thereby further accelerating the reaction of dehydrating sugars to produce HMF in the first heating step, and further accelerating the reaction of oxidizing HMF to produce DFF in the second heating step.

[0029] The heating temperature in the first heating step is preferably 80 to 140°C, more preferably 100 to 140°C, and even more preferably 120 to 140°C, from the viewpoint of further promoting the reaction of dehydrating saccharides to produce HMF. The heating time in the first heating step is preferably 0.5 to 10 hours, more preferably 0.5 to 5 hours, and even more preferably 0.5 to 2 hours, from the viewpoint of further promoting the reaction of dehydrating sugars to produce HMF.

[0030] The first heating step is preferably carried out in the presence of a first acid catalyst. The first acid catalyst is preferably one of the above-mentioned acid catalysts, but from the viewpoint of efficiently reacting sugars having a glucose skeleton in addition to sugars having a fructose skeleton to further promote the production of HMF, iron halide or aluminum halide is preferred, and iron chloride hexahydrate is more preferred.

[0031] <Second heating process> The heating temperature in the second heating step is preferably 110 to 180°C, more preferably 120 to 170°C, and even more preferably 140 to 150°C, from the viewpoint of further promoting the reaction of oxidizing HMF to produce DFF. The heating time in the second heating step is preferably 0.5 to 10 hours, more preferably 1 to 7 hours, and even more preferably 2 to 4 hours, from the viewpoint of further promoting the reaction of oxidizing HMF to produce DFF.

[0032] It is preferable to add the second acid catalyst during the period from the middle of the first heating step to the middle of the second heating step. The second acid catalyst is preferably the above-mentioned acid catalyst, but from the viewpoint of further promoting the reaction of oxidizing HMF to produce DFF, preferred are acetic acid, oxalic acid, oxalic acid dihydrate, formic acid, toluenesulfonic acid, hydrochloric acid, and sulfuric acid, and more preferred are oxalic acid, oxalic acid dihydrate, and formic acid. [Extraction process] This step involves adding an organic solvent to the DFF-containing solution obtained by the heating step, thereby extracting the DFF into the organic solvent. From the viewpoint of suitable extraction of DFF, examples of the organic solvent include toluene, hexane, chloroform, and dichloromethane, and toluene is preferred.

[0033] [Cleaning process] This step is a step in which the DFF-containing organic solvent obtained in the extraction step is washed with a washing liquid, and preferably components such as by-products and reaction catalysts are removed. The cleaning liquid may be a basic aqueous solution such as an aqueous sodium bicarbonate solution, or saline solution, and is preferably at least one of an aqueous sodium bicarbonate solution and saline solution, and more preferably a combination of an aqueous sodium bicarbonate solution and saline solution.

[0034] [Dehydration process] This step is a step of removing water from the organic layer after the washing step using a dehydrating agent. Examples of the dehydrating agent include anhydrous inorganic salts such as magnesium sulfate and sodium sulfate, and molecular sieves, with anhydrous magnesium sulfate being preferred. Thereafter, impurities in the dehydrated organic layer may be removed by filtration or the like.

[0035] [Recovery process] This step is a step of isolating and recovering DFF from the organic layer dehydrated in the dehydration step. In this step, it is preferable to isolate and recover DFF by distilling off the organic solvent from the organic layer. Furthermore, during or after this step, a purification procedure such as recrystallization or sublimation may or may not be included. [Example]

[0036] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these.

[0037] The compounds used in the examples and comparative examples are as follows. (1) Sugars Fructose (Fujifilm Wako Pure Chemical Industries, Ltd., product name "D(-)-fructose", purity 99.0% or higher) Glucose (Fujifilm Wako Pure Chemical Industries, Ltd., trade name "D(+)-glucose", purity 98.0% or more) (2) Sulfoxide compound (reaction solvent) Dimethyl sulfoxide (DMSO) (3) Organic Solvent N-methylpyrrolidone (NMP) Dimethylformamide (DMF) (4) Halide salts Sodium bromide (5) Acid catalyst Iron chloride hexahydrate (FeCl3·6H2O) Oxalic acid dihydrate ((COOH)2·2H2O) Formic acid (6) Extraction solvent ·toluene (7) Other Sodium bicarbonate Salt Anhydrous magnesium sulfate

[0038] DFF was analyzed by the following method: the compound obtained by the reaction was dissolved in deuterated chloroform and analyzed by a nuclear magnetic resonance spectrometer. 1 H-NMR measurements were carried out. < 1 H-NMR measurement conditions Equipment: Nuclear magnetic resonance equipment "ECZ-500R / S1" manufactured by JEOL Ltd. Solvent: deuterated chloroform Nuclide: 1 H Measurement temperature: 20℃ Accumulation count: 32 times

[0039] [Example 1] A 500 mL reaction vessel equipped with a thermometer and a stirrer was charged with 20 g of fructose as a sugar and 200 g of dimethyl sulfoxide as a sulfoxide compound, and the mixture was stirred at room temperature to dissolve. After dissolution, 1.4 g of iron chloride hexahydrate as an acid catalyst and 10 g of sodium bromide as a halide salt were added. The mixture was heated to 130°C under atmospheric pressure with stirring and allowed to react for 1 hour (first heating step). Next, 2 g of oxalic acid dihydrate was added as an acid catalyst, and the mixture was heated to 150°C and allowed to react for 3 hours (second heating step). No bubbling was performed during the first and second heating steps. After the reaction, toluene was added and extraction was carried out. This toluene solution was separated into aqueous sodium bicarbonate solution and saturated saline solution. After separation, anhydrous magnesium sulfate was added to the organic layer for dehydration, and insoluble matter was removed by filtration. After filtration, the solvent was distilled off to obtain DFF (2,5-diformylfuran) crystals. This DFF crystals was recrystallized to obtain DFF. The yield of DFF was 58%. 1 H-NMR(500MHz,CDCl3): δ 7.36(d,2H), 9.87(s,2H)

[0040] [Examples 2 to 4 and Comparative Example 1] The yield of DFF was measured in the same manner as in Example 1, except that the composition of raw materials and reaction conditions were as shown in Table 1. The results are shown in Table 1.

[0041] [Example 5] A 500 mL reaction vessel equipped with a thermometer and a stirrer was charged with 20 g of fructose as a sugar and 200 g of dimethyl sulfoxide as a sulfoxide compound, and the mixture was stirred at room temperature to dissolve. After dissolution, 1.4 g of iron chloride hexahydrate and 1.8 g of formic acid were added as acid catalysts, and 10 g of sodium bromide as a halide salt. The mixture was heated to 130°C under atmospheric pressure with stirring and reacted for 3 hours. After the reaction, toluene was added and extraction was performed. The toluene solution was separated with aqueous sodium bicarbonate and saturated saline. The organic layer after separation was dehydrated with anhydrous magnesium sulfate, and insoluble matter was removed by filtration. After filtration, the solvent was distilled off to obtain DFF (2,5-diformylfuran) crystals. The DFF crystals were recrystallized to obtain DFF. The yield of DFF was 18%.

[0042] [Example 6] The yield of DFF was measured in the same manner as in Example 5, except that the heating temperature was 150° C. The results are shown in Table 1. [Comparative Examples 2 and 3] The yield of DFF was measured in the same manner as in Example 1, except that the organic solvents shown in Table 1 were used instead of the sulfoxide compound. The results are shown in Table 1.

[0043] [Table 1]

[0044] According to Examples 1 to 6, DFF could be produced from sugars in one pot. In Examples 1, 3, and 4, the first heating step was carried out in the presence of an acid catalyst (iron chloride hexahydrate) suitable for producing HMF, and the second heating step was carried out in the presence of an acid catalyst (oxalic acid dihydrate or formic acid) suitable for producing DFF, thereby enabling the production of DFF in a higher yield. However, as in Examples 5 and 6, even when the heating step was performed in one step at a constant temperature instead of in two steps at different temperatures, DFF could be produced with a good yield. In Example 1, the second heating step was carried out in the presence of oxalic acid dihydrate, which is suitable for producing DFF, and therefore the yield of DFF was improved compared to Example 2, in which the second heating step was carried out in the absence of oxalic acid dihydrate. As shown in Example 3, according to the production method of the present invention, DFF can be produced even when glucose is used as a raw material. In Example 4, the second heating step was carried out in the presence of formic acid, which is suitable for producing DFF, and therefore the yield was improved compared to Example 2, in which the second heating step was carried out in the absence of formic acid. On the other hand, DFF could not be produced in Comparative Example 1 because no halide salt was used, and DFF could not be produced in Comparative Examples 2 and 3 because other organic solvents were used instead of sulfoxide compounds as solvents.

Claims

1. A method for producing 2,5-diformylfuran, comprising a heating step of heating a sugar in the presence of a sulfoxide compound and a halide salt to react the sugar and produce 2,5-diformylfuran.

2. 2. The method for producing 2,5-diformylfuran according to claim 1, wherein the halide salt is a salt of a halide ion with at least one of an alkali metal ion and an alkaline earth metal ion.

3. 3. The method for producing 2,5-diformylfuran according to claim 1, wherein in the heating step, the saccharide is further heated in the presence of an acid catalyst to react with the saccharide to produce 2,5-diformylfuran.

4. 4. The method for producing 2,5-diformylfuran according to claim 3, wherein the acid catalyst is at least one selected from the group consisting of Lewis acids and Bronsted acids.

5. The method for producing 2,5-diformylfuran according to claim 1 or 2, wherein the heating temperature in the heating step is 80 to 180°C.

6. 3. The method for producing 2,5-diformylfuran according to claim 1, wherein the heating step comprises a first heating step and a second heating step at a temperature higher than that of the first heating step.

7. 7. The method for producing 2,5-diformylfuran according to claim 6, wherein the first heating step is further carried out in the presence of a first acid catalyst.

8. 8. The method for producing 2,5-diformylfuran according to claim 7, wherein a second acid catalyst is added during a period from the middle of the first heating step to the middle of the second heating step.

9. The method for producing 2,5-diformylfuran according to claim 1 or 2, wherein the saccharide is a sugar having at least one skeleton selected from the group consisting of a fructose skeleton and a glucose skeleton.

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