Process for producing alkyl furan carboxylate

Abstract

To provide a novel method for producing an alkyl furancarboxylic acid ester.SOLUTION: The method for producing an alkyl furancarboxylic acid ester comprises performing an oxidation-reduction reaction between an alkyl furanaldehyde and a compound represented by A-OH (where A represents a C1-10 organic group) using a base and a solvent in the presence of an N-heterocyclic carbene catalyst. An effective catalyst amount is 0.005 mole or more per 1 mole of an alkyl furancarboxylic acid, and a molar ratio of base / catalyst is 0.08 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] An object of the present invention is to provide a method for producing an alkyl furan carboxylate. In particular, the present invention relates to a method for producing an alkyl furan carboxylate using an alkyl furan aldehyde as a starting material.

Background Art

[0002] Conventionally, methods for producing alkyl furan carboxylates have been studied. For example, Non-Patent Document 1 describes the production of 5-methyl-2-furoate and the like from 5-(chloromethyl)-2-furaldehyde (chloromethylfurfural).

Chemical Formula

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the method described in Non-Patent Document 1 above, the reaction may not proceed properly even when a sufficient amount of catalyst and base are used. That is, a new method for producing an alkyl furan carboxylate is required. In particular, a method for producing an alkyl furan carboxylate in which the reaction proceeds sufficiently even with a small amount of base is required. An object of the present invention is to solve such problems and to provide a new method for producing an alkyl furan carboxylate.

Means for Solving the Problems

[0005] Under the above problems, as a result of the study by the present inventor, as a starting material, instead of chloromethylfurfural, an alkyl furan aldehyde is used, and a nucleophile (alcohol) is reacted in the presence of a catalyst, a base and a solvent, and by adjusting so as to satisfy a predetermined effective catalyst amount and a predetermined molar ratio of base / catalyst, it has been found that the nucleophilic reaction to the alkyl furan carboxylic acid ester can proceed sufficiently, and the present invention has been completed. Specifically, the above problems have been solved by the following means. <1>A method for producing an alkyl furan carboxylic acid ester, which comprises performing an oxidation-reduction reaction between an alkyl furan aldehyde and a compound represented by A-OH (where A is an organic group having 1 to 10 carbon atoms) using a base and a solvent in the presence of an N-heterocyclic carbene catalyst, wherein the effective catalyst amount is 0.005 mol or more per 1 mol of the alkyl furan aldehyde, and the molar ratio of base / catalyst is 0.08 or more. <2>The method for producing an alkyl furan carboxylic acid ester according to <1>, wherein the molar ratio of the base / catalyst is 0.08 or more and 20.0 or less. <3>The method for producing an alkyl furan carboxylic acid ester according to <1> or <2>, wherein the base contains at least one of diazabicycloundecene, sodium carbonate, sodium hydroxide, triethylamine, sodium methoxide, and potassium carbonate. <4>The method for producing an alkyl furan carboxylic acid ester according to any one of <1> to <3>, wherein the effective catalyst amount is 0.01 mol or more per 1 mol of the alkyl furan aldehyde. <5>The method for producing an alkyl furan carboxylic acid ester according to any one of <1> to <4>, wherein the molar ratio of the base / catalyst is 0.5 or more. <6>The method for producing an alkyl furan carboxylic acid ester according to any one of <1> to <5>, wherein the N-heterocyclic carbene catalyst has a pKa calculated from the free energy of 33.0 or less, obtained by determining the stable structure of the catalyst molecule in methanol by the SMD method using Gaussian16. <7>The method for producing an alkyl furan carboxylate according to <6>, wherein the pKa of the N-heterocyclic carbene catalyst is 20.0 or more. <8>The method for producing an alkyl furan carboxylate according to any one of <1> to <7>, wherein the N-heterocyclic carbene catalyst contains at least one selected from the group consisting of triazolium, imidazolinium, imidazolium, and thiazolium. <9>The method for producing an alkyl furan carboxylate according to any one of <1> to <8>, wherein the N-heterocyclic carbene catalyst contains at least one catalyst represented by the following formula (C).

Chemical formula

Chemical formula

Chemical formula

Chemical formula

Advantages of the Invention

[0006] The present invention enables the provision of a new method for producing an alkyl furan carboxylate.

Best Mode for Carrying Out the Invention

[0007] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. It should be noted that the following present embodiment is an exemplification for explaining the present invention, and the present invention is not limited only to the present embodiment. In this specification, "~" is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value. In this specification, various physical property values and characteristic values are those at 23°C unless otherwise specified. In the notation of a group (atomic group) in this specification, a notation that does not describe substitution and unsubstitution includes both a group (atomic group) having no substituent and a group (atomic group) having a substituent together with the group (atomic group) having no substituent. For example, the "alkyl group" includes not only an alkyl group having no substituent (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group). In this specification, a notation that does not describe substitution and unsubstitution preferably means unsubstituted. When the standards shown in this specification differ depending on the year and the measurement method, etc., they are based on the standards as of January 1, 2021 unless otherwise specified.

[0008] The method for producing an alkyl furan carboxylic acid ester according to the present embodiment is a method for producing an alkyl furan carboxylic acid ester in which, in the presence of an N-heterocyclic carbene catalyst, a base and a solvent are used, and a redox reaction is carried out between an alkyl furan aldehyde and a compound represented by A-OH (where A is an organic group having 1 to 10 carbon atoms), and the effective catalyst amount is 0.005 mol or more with respect to the alkyl furan aldehyde, and the molar ratio of the base / catalyst is 0.08 or more. By adopting such a configuration, a redox reaction can be effectively advanced between an alkyl furan aldehyde and a compound represented by A-OH (where A is an organic group having 1 to 10 carbon atoms), and an alkyl furan carboxylic acid ester can be produced in a high yield.

[0009] In the manufacturing method of the present embodiment, the alkyl furan aldehyde serves as a substrate for the redox reaction, and usually, the alkyl furan aldehyde is introduced into the reaction system. However, the alkyl furan aldehyde may also be an intermediate for producing the alkyl furan carboxylic acid ester.

[0010] The number of carbon atoms of the alkyl group having 1 to 10 carbon atoms in the alkyl furan aldehyde is preferably 8 or less, more preferably 6 or less, still more preferably 5 or less, even more preferably 4 or less, even still more preferably 3 or less, may be 2 or less, and further may be 1.

[0011] The molecular weight of the alkyl furan aldehyde is preferably from 111 to 500, and more preferably from 111 to 300.

[0012] The alkyl furan aldehyde is preferably a compound represented by the formula (F1).

Chemical formula

[0013] The number of carbon atoms of the alkyl group of R is preferably 8 or less, more preferably 6 or less, still more preferably 5 or less, even more preferably 4 or less, even still more preferably 3 or less, may be 2 or less, and may be 1. Specific examples of R include a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an isobutyl group, an n-butyl group, and a tert-butyl group. A methyl group, an ethyl group, and an isopropyl group are preferred, and a methyl group is more preferred.

[0014] In the present embodiment, only one kind of alkyl furan aldehyde may be used, or two or more kinds may be used.

[0015] The target product of the production method of this embodiment is an alkyl furan carboxylate. Usually, the alkyl furan carboxylate (product mixture) generated from the reaction system is taken out, and if necessary, separated from the catalyst or impurities (by-products) are removed. However, the alkyl furan carboxylate may be an intermediate for producing other compounds. That is, further reactions may proceed within the same reaction system.

[0016] The alkyl group of the alkyl furan carboxylate (the alkyl group corresponding to R in formula (F2)) is the same as the alkyl group of the alkyl furan aldehyde (the alkyl group corresponding to R in formula (F1)). The alkyl furan carboxylate is preferably a compound represented by formula (F2). [Chemical formula] (In formula (F2), R is an alkyl group having 1 to 10 carbon atoms, and A is an organic group having 1 to 10 carbon atoms.) R has the same meaning as R in formula (F1). A has the same meaning as A in the compound represented by A-OH.

[0017] In the production method of this embodiment, an oxidation-reduction reaction is carried out between an alkyl furan aldehyde and a compound represented by A-OH (where A is an organic group having 1 to 10 carbon atoms). That is, the compound represented by A-OH acts as a nucleophile that nucleophilically attacks the formyl group of the alkyl furan aldehyde. The organic group having 1 to 10 carbon atoms, which is A in A-OH, is preferably a hydrocarbon group having 1 to 10 carbon atoms, a group composed of a combination of a hydrocarbon group having 1 to 10 carbon atoms and -O- and / or -C(=O)-, more preferably a group composed of a combination of an alkyl group having 1 to 10 carbon atoms and -O- and / or -C(=O)-, and most preferably an alkyl group having 1 to 10 carbon atoms. The number of carbon atoms of A is preferably 8 or less, more preferably 6 or less, still more preferably 5 or less, even more preferably 4 or less, even still more preferably 3 or less, and may be 2 or less, or may be 1. The hydrocarbon group as A is preferably a linear, branched or cyclic alkyl group or aryl group, and more preferably a linear alkyl group (primary alcohol). By using a primary alcohol, the reactivity is more improved and the yield tends to be higher. The molecular weight of the compound represented by A-OH is preferably 32 or more, preferably 500 or less, more preferably 300 or less, still more preferably 200 or less, and even still more preferably 100 or less.

[0018] Examples of the compound represented by A-OH include methanol, ethanol, isopropanol, isobutanol, n-propanol, n-butanol, and the compounds shown below.

Chemical formula

[0019] The compound represented by A-OH in the present embodiment may be the same substance as the solvent described in detail later. For example, the case where both the compound represented by A-OH and the solvent are methanol is exemplified.

[0020] In the oxidation-reduction reaction, the amount of the compound (nucleophile) represented by A-OH with respect to 1 mol of the substrate is preferably 1 mol or more, more preferably more than 1 mol, even more preferably 1.5 mol or more, and even still more preferably 2.5 mol or more. Also, the amount of the compound (nucleophile) represented by A-OH with respect to 1 mol of the substrate is preferably 20 mol or less, more preferably 10 mol or less, still more preferably 8 mol or less, even still more preferably 5 mol or less, and even still more preferably 4 mol or less. In the redox reaction of the present embodiment, only one kind of the compound represented by A-OH may be used, or two or more kinds may be used. When two or more kinds are used, it is preferable that the total amount is within the above range. In addition, when the compound represented by A-OH is also used as a solvent, its blending amount is the same as the preferable range of the blending amount of the solvent.

[0021] In the production method of the present embodiment, a redox reaction is carried out in the presence of an N-heterocyclic carbene catalyst. By using the N-heterocyclic carbene catalyst, the reaction proceeds more effectively. The N-heterocyclic carbene catalyst is not particularly limited as long as a part or all of it is dissolved in a solvent (reaction solvent). Preferably, 90% by mass or more, more preferably 95% by mass or more, particularly preferably 99% by mass or more, and even more particularly preferably 100% by mass of it is soluble in the solvent at the reaction temperature. The N-heterocyclic carbene catalyst preferably has a pKa (hereinafter sometimes simply referred to as "pKa of the N-heterocyclic carbene catalyst") calculated from the free energy and obtained by determining the stable structure of the catalyst molecule in methanol from the solvation model (SMD: solvation model density) using Gaussian16, which is 33.0 or less. More specifically, for the calculation of the pKa of the N-heterocyclic carbene catalyst, the software Gaussian16 was used to perform a structure optimization calculation of the gaseous molecule under the conditions of B3LYP / 6-31+G(d). A vibration calculation was performed on the obtained structure to confirm that it is a stable structure without imaginary vibrations. When determining the stable structure, the conformations before and after acid dissociation were made the same except for the presence or absence of hydrogen. The free energies of the gaseous state and the molecule in the solvent at 298.15 K were determined by a single-point calculation using M06-2X / 6-311++G(d,p). At this time, SMD was adopted as the solvation model to consider the solvent effect. Methanol was used as the solvent. The free energy of dissolution of the proton was adopted as "-255.6 kcal / mol". From the free energies of each state obtained using this method, the free energy difference ΔGsoln before and after acid dissociation was determined, and the pKa was determined. By using the N-heterocyclic carbene catalyst obtained by the above method, the conversion rate of alkyl furan aldehyde can be increased, and the reaction rate (reaction cycle) of the reaction system can be increased.

[0022] The pKa of the N-heterocyclic carbene catalyst is preferably 32.0 or less, more preferably 31.5 or less, and further preferably 31.0 or less, 30.5 or less, 30.0 or less, 29.5 or less, 29.0 or less, 28.5 or less, 28.0 or less, 27.5 or less, 27.0 or less, 26.5 or less, 26.0 or less, 25.5 or less, 25.0 or less in this order. By setting it below the upper limit value, the yield of the obtained alkyl furan carboxylic acid ester is further improved. Also, the pKa of the N-heterocyclic carbene catalyst is preferably 15.0 or more, more preferably 16.0 or more, and further preferably 17.0 or more, 17.5 or more, 18.0 or more, 18.5 or more, 19.0 or more, 19.5 or more, 20.0 or more, 20.5 or more, 21.0 or more, 21.5 or more, 22.0 or more, 22.5 or more, 23.0 or more in this order. In the redox reaction of this embodiment, only one kind of N-heterocyclic carbene catalyst may be used, or two or more kinds may be used. When two or more kinds are used, each N-heterocyclic carbene catalyst shall satisfy the above preferable range.

[0023] The N-heterocyclic carbene catalyst causes the reaction to proceed by the action of a base. The N-heterocyclic carbene catalyst preferably contains at least one selected from the group consisting of triazolium, imidazolinium, imidazolium and thiazolium, more preferably contains at least one selected from the group consisting of triazolium, imidazolinium, and imidazolium, still more preferably contains at least one selected from the group consisting of triazolium and imidazolinium, and even more preferably contains at least one kind of triazolium.

[0024] More specifically, it is preferable that the N-heterocyclic carbene catalyst contains at least one kind of catalyst represented by the following formula (C). [Chemical formula] (In formula (C), R C1 and R C2 each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, a heteroaryl group having 4 to 16 carbon atoms, a halogenated alkyl group having 1 to 12 carbon atoms, a halogenated aryl group having 6 to 18 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms. Z represents -S- or -NR c3 -. X is a methine group (=CR C5 -), a nitrogen atom (=N-), or a methylene group (-CR C6 2-). When X is a methine group or a nitrogen atom, the dashed line in the formula represents a double bond, and when X is a methylene group, the dashed line in the formula represents a single bond. In the formula, R C3 , R C5 and R C6 each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 2 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an acyl group having 2 to 12 carbon atoms, a hydroxy group, a carboxy group, or a halogen atom. Y - represents a counter anion. R C2 and R C3 , R C2 and R C5 , R C2 and R C6 , R C1 and R C5 , R C1 and R C6 may each be bonded to or condensed with each other to form a ring.) The two Rs C6 contained in the above methylene group (-CR C6 2-) may be the same or different. Hereinafter, when there are two or more groups with the same symbol in one compound, the two or more groups with the same symbol may each be the same or different.)

[0025] In the present embodiment, the alkyl group is intended to include a cycloalkyl group in addition to linear and branched alkyl groups. Further, the alkylaryl group and arylalkyl group are intended to include a group in which a cyclic alkyl and aryl (for example, benzene ring) are condensed.

[0026] R C1 and R C2 each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, a halogenated aryl group having 6 to 12 carbon atoms, an alkylaryl group having 7 to 13 carbon atoms, or an arylalkyl group having 7 to 13 carbon atoms. The halogen atom contained in the halogenated alkyl group and halogenated aryl group is preferably a fluorine atom and a chlorine atom.

[0027] R C3 、R C5 and R C6 each independently is preferably a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an acyl group having 2 to 7 carbon atoms, a hydroxy group, a carboxy group, or a halogen atom, more preferably a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, still more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and most preferably a hydrogen atom.

[0028] The monovalent anion is not particularly limited as long as it is a monovalent anion, but Y - is preferably an anion containing a halogen, and F - 、Cl - 、Br - 、I - 、BF4 - is preferred.

[0029] When the catalyst represented by the above formula (C) has a methine group in X, it is preferably represented by the following formula (C2).

Chemical formula

[0030] R 11 and R 31 are each independently preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms. R 21 , R 51 is preferably a hydrogen atom.

[0031] When the catalyst represented by the above formula (C) has a methylene group at X, it is preferably represented by the following formula (C3).

Chemical formula

[0032] R 12 and R 32 are each independently preferably an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms. R 22 , R 62 is preferably a hydrogen atom.

[0033] When the catalyst represented by the above formula (C) has a nitrogen atom at X, it is preferably represented by the following formula (C4).

Chemical formula

[0034] R 13 and R 33 are each independently preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 5 carbon atoms, still more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group. R 23 is preferably a hydrogen atom.

[0035] When the catalyst represented by the above formula (C4) forms a ring with R 23 and R 33 , it is preferably represented by the following formula (C5).

Chemical formula

[0036] R 14 is preferably a halogenated aryl group having 6 to 18 carbon atoms or an alkylaryl group having 7 to 20 carbon atoms. R 74 R 84 R 94 is preferably a hydrogen atom.

[0037] When the catalyst represented by the above formula (C) has a sulfur atom at Z, it is preferably represented by the following formula (C4).

Chemical formula

[0038] In this embodiment, the catalyst represented by formula (C4) is particularly preferred.

[0039] Examples of the catalyst include the following compounds. Needless to say, the present embodiment is not limited thereto.

Chemical formula

Chemical formula

Chemical formula

[0040] In the redox reaction, the amount of the N-heterocyclic carbene catalyst relative to 1 mole of the substrate is preferably 0.0001 mole or more, more preferably 0.001 mole or more, still more preferably 0.01 mole or more, even more preferably 0.05 mole or more, yet even more preferably 0.1 mole or more, and still even more preferably 0.2 mole or more. By setting the amount to be the above lower limit or more, the redox reaction tends to proceed more effectively. The amount of the catalyst relative to 1 mole of the substrate is preferably 5.0 moles or less, more preferably 3.0 moles or less, still more preferably 1.0 moles or less, even more preferably 0.5 moles or less, and yet even more preferably 0.4 moles or less. In the redox reaction of this embodiment, only one kind of the N-heterocyclic carbene catalyst may be used, or two or more kinds may be used. When two or more kinds are used, it is preferable that the total amount is within the above range.

[0041] In the production method of this embodiment, the redox reaction is carried out in the presence of a base. By carrying out the reaction in the presence of a base, the yield of the alkyl furan carboxylic acid ester is improved. The base may be an organic base or an inorganic base. Examples include alkylamine, alkanolamine, polyamine, hydroxylamine, cyclic amine, quaternary ammonium, alkali metal-containing compound, and alkaline earth metal-containing compound. Alkylamine, polyamine, cyclic amine, and alkali metal-containing compound are preferable, and diazabicycloundecene, sodium carbonate, sodium hydroxide, triethylamine, sodium methoxide, and potassium carbonate are more preferable. It is preferable to contain at least one of diazabicycloundecene, sodium carbonate, and potassium carbonate, more preferably to contain diazabicycloundecene and / or sodium carbonate, and still more preferably to contain diazabicycloundecene.

[0042] In this embodiment, the effective catalyst amount is 0.005 mol or more. The effective catalyst amount means the smaller number of moles between the amount of the catalyst added and the amount of the base with respect to 1 mol of the substrate. It is presumed that the base and the catalyst actually contribute to the redox reaction within this amount range. The effective catalyst amount is preferably 0.01 mol or more, more preferably 0.02 mol or more, still more preferably 0.04 mol or more, even more preferably 0.1 mol or more, and yet even more preferably 0.2 mol or more with respect to 1 mol of the alkylfuranaldehyde. By setting the lower limit value or more, the yield of the alkylfurancarboxylic acid ester tends to be further improved. The upper limit value of the effective catalyst amount is not particularly defined, but from the viewpoint of reducing the amount of the base and the catalyst, it is more preferably 1.0 mol or less, even more preferably 0.8 mol or less, and yet even more preferably 0.5 mol or less.

[0043] Further, in this embodiment, the molar ratio of the base / catalyst is 0.08 or more. By setting such a mass ratio, the yield of the alkylfurancarboxylic acid ester can be increased. The molar ratio of the base / catalyst is preferably 0.1 or more, more preferably 0.3 or more, still more preferably 0.5 or more, and even more preferably 0.8 or more. The molar ratio of the base / catalyst is also preferably 20.0 or less, more preferably 10.0 or less, still more preferably 8.0 or less, even more preferably 4.0 or less, yet even more preferably 3.0 or less, and still even more preferably 2.0 or less. In this embodiment, in particular, even when the molar ratio of the base / catalyst is 4.0 or less, further 3.0 or less, and particularly 2.0 or less, a high yield can be achieved and the amount of the base used can be reduced.

[0044] The production method of this embodiment preferably further performs the redox reaction in the presence of an oxidizing agent. By using an oxidizing agent, the progress of side reactions can be more effectively suppressed. The type of the oxidizing agent is not particularly defined and may be an organic compound or an inorganic compound. The amount of the oxidizing agent can be appropriately determined according to the type of the oxidizing agent. For example, the amount of the oxidizing agent relative to 1 mole of the substrate is preferably 0.01 mole or more and preferably 20.0 moles or less. In the redox reaction of the present embodiment, only one type of oxidizing agent may be used, or two or more types may be used. When two or more types are used, it is preferable that the total amount is within the above range.

[0045] In the present embodiment, when the oxidizing agent is an organic compound, examples thereof include quinone, nitrobenzene, hypervalent organic iodine compounds such as 2-iodobenzoic acid, nitroxyl radical compounds such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), and organic peroxides such as m-chlorobenzoic acid, and quinone is preferable. Here, quinone means a compound in which two hydrogen atoms bonded to the benzene ring of an aromatic hydrocarbon are each replaced with an oxygen atom. In addition, the oxidizing agents described in the 3rd Edition of Oxidizing Agents for Organic Synthesis published by Fujifilm Wako Pure Chemical Corporation can also be used, and the contents thereof are incorporated herein.

[0046] The molecular weight of quinone as the oxidizing agent is preferably 108 or more, preferably 1000 or less, more preferably 800 or less, and may be 600 or less.

[0047] Preferably, the oxidizing agent contains at least one kind of the oxidizing agent represented by the formula (O).

Chemical formula

[0048] R 1 ~R 8 are each independently preferably a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms, more preferably each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms, and even more preferably each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0049] When m in formula (O) is 0, and R 1 and R 2 , R 3 and R 4 are each condensed with each other to form a 6-membered ring, an example is shown in the following formula (O-1).

Chemical formula

[0050] R 101 ~R 108 each independently represent a group synonymous with the above R 1 , and a hydrogen atom or an alkyl group having 1 to 6 carbon atoms is preferred.

[0051] In formula (O), when m is 1 and R 1 and R 2 , R 3 and R 4 , R 5 and R 6 , R 7 and R 8 are each condensed with one another to form a 6-membered ring, an example is represented by the following formula (O-2). [Chemical formula] (In formula (O-2), R 201 ~R 204 each independently represent a group synonymous with R 1 in formula (O).)

[0052] R 201 ~R 204 each independently represent a group synonymous with the above R 1 , and a hydrogen atom is preferred. n1, n2, n3, and n4 each independently represent an integer from 1 to 4.

[0053] In formula (O), when m is 1 and R 1 and R 2 , R 3 and R 4 , R 5 and R 6 , R 7 and R 8 are each not condensed with one another to form a ring, an example is represented by the following formula (O-3). [Chemical formula] (In formula (O-3), R 301 ~R 308 each independently represent a group synonymous with R 1 in formula (O).)

[0054] R 301 ~R 308 each independently represent a group synonymous with the above R 1 , and a hydrogen atom or an alkyl group having 1 to 12 carbon atoms is preferred, and a hydrogen atom or an alkyl group having 1 to 8 carbon atoms is more preferred.

[0055] m in formula (O) is 0, and R 1 and R 2 , R 3 and R 4 An example of a group in which the groups are not condensed with each other to form a ring is the group represented by the following formula (O-4). [ka] (In formula (O-4), R 401 ~R 404 each independently represents R in formula (O) 1 represents a group having the same meaning as R 401 ~R 404 are each independently the above R 1 R is preferably a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and further preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. 401 ~R 404 When is an alkyl group or an alkoxy group, the alkyl group or the alkoxy group may have a halogen atom as a substituent bonded to a carbon atom in the formula.

[0056] In this embodiment, formulae (O-1), (O-3) and (O-4) are preferred, formulae (O-3) and (O-4) are more preferred, and formula (O-3) is even more preferred.

[0057] Examples of the oxidizing agent include the following compounds. It goes without saying that the present embodiment is not limited to these. Note that tBu is a tert-butyl group. [ka] [ka] [ka] [ka]

[0058] In the oxidation-reduction reaction, the amount of quinone relative to 1 mol of the substrate is preferably 0.01 mol or more, more preferably 0.05 mol or more, still more preferably 0.1 mol or more, even more preferably 0.5 mol or more, and even more preferably 0.8 mol or more. By setting the amount to be not less than the lower limit value, the yield of the alkyl furan carboxylate tends to be further improved. Also, the amount of the oxidizing agent relative to 1 mol of the substrate may be 3.0 mol or less, may be 2.5 mol or less, may be 2.0 mol or less, may be 1.5 mol or less, or may be 1.2 mol or less. In the oxidation-reduction reaction of the present embodiment, only one kind of quinone may be used, or two or more kinds may be used. When two or more kinds are used, it is preferable that the total amount is within the above range.

[0059] In the present embodiment, when the oxidizing agent is an inorganic compound, examples thereof include permanganates such as potassium permanganate; chromic acids such as potassium dichromate and chromium oxide; nitrates such as nitric acid and potassium nitrate; halogens such as fluorine, chlorine, bromine, and iodine; peroxides such as hydrogen peroxide solution and sodium peroxide; oxides such as copper(II) oxide, lead(IV) oxide, and manganese(IV) oxide; and metal salts such as iron chloride and copper sulfate. Oxides are preferable, and manganese oxide is more preferable.

[0060] In the oxidation-reduction reaction, the amount of the inorganic compound as the oxidizing agent relative to 1 mol of the substrate is preferably 1.00 mol or more, more preferably 3.00 mol or more, still more preferably 5.00 mol or more, and preferably 20.0 mol or less, more preferably 15.0 mol or less, and still more preferably 10.0 mol or less. In the oxidation-reduction reaction of the present embodiment, only one kind of the inorganic compound as the oxidizing agent may be used, or two or more kinds may be used. When two or more kinds are used, it is preferable that the total amount is within the above range.

[0061] In the production method of this embodiment, the redox reaction is preferably carried out in the presence of a solvent. The solvent is not particularly limited as long as it can dissolve part or all of the alkylfurfural and does not interfere with the redox reaction. Examples of the solvent used in the production method of this embodiment include aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, amide solvents, ether solvents, alcohol solvents, halogen solvents, ester solvents, etc. Aromatic hydrocarbon solvents, ether solvents, and alcohol solvents are preferred, and ether solvents and sulfoxide solvents are more preferred.

[0062] Specific examples of the aromatic hydrocarbon solvent include benzene, toluene, etc. Specific examples of the amide solvent include acetonitrile, N,N-dimethylacetamide, N,N-dimethylformamide, etc. Specific examples of the ether solvent include tetrahydrofuran (hereinafter also referred to as THF), diethyl ether, etc. Specific examples of the alcohol solvent include methanol, ethanol, isopropanol, etc. The alcohol solvent can also act as a nucleophile. Specific examples of the halogen solvent include dichloromethane, dichloroethane, chloroform, etc. Specific examples of the ester solvent include ethyl acetate, etc. Specific examples of the sulfoxide solvent include dimethyl sulfoxide, etc.

[0063] In the redox reaction, the amount of the solvent used is not particularly limited. However, from the viewpoints of productivity and energy efficiency, it is preferably 0.5 times or more by mass, more preferably 0.8 times or more by mass, still more preferably 1.0 times or more by mass, based on the substrate (alkylfurfural). Also, the amount of the solvent used is preferably 200 times or less by mass, more preferably 100 times or less by mass, still more preferably 50 times or less by mass, and even more preferably 30 times or less by mass, based on the substrate. In the redox reaction, only one kind of solvent may be used, or two or more kinds may be used. When two or more kinds are used, it is preferable that the total amount is within the above range.

[0064] The reaction temperature of the redox reaction in the production method of this embodiment is not particularly limited, but is preferably -80°C or higher, more preferably 0°C or higher, still more preferably 15°C or higher, even more preferably 20°C or higher, and even more preferably 25°C or higher. Further, the reaction temperature of the redox reaction is preferably 200°C or lower, more preferably 150°C or lower, still more preferably 100°C or lower, even more preferably 50°C or lower, and even more preferably 40°C or lower. In the production method of this embodiment, the reaction temperature may be the same temperature (however, a variation of ±5°C is regarded as an error) except for the first temperature increase and the last temperature decrease, or the reaction may be carried out in two or more stages of reaction. In this embodiment, it is preferable that the reaction temperature is the same temperature (however, a variation of ±5°C is regarded as an error) except for the first temperature increase and the last temperature decrease.

[0065] The reaction time of the redox reaction in the production method of this embodiment is preferably 1 minute or longer, and may be 30 minutes or longer, 1 hour or longer, or 1.5 hours or longer. Further, the reaction time of the redox reaction is preferably 50 hours or shorter, and may be 30 hours or shorter, or 25 hours or shorter.

[0066] The separation of the reaction mixture and the catalyst after the reaction can be carried out by common methods such as sedimentation, centrifugation, filtration, etc. The separation of the catalyst is preferably carried out under an inert gas atmosphere such as nitrogen or argon as appropriate to prevent ignition, depending on the catalyst used. Further, the reaction mixture may be used as it is as a raw material or an intermediate after concentrating the obtained reaction solution as necessary, or the reaction mixture may be appropriately post-treated and purified. Specific methods of post-treatment include known purification methods such as extraction, distillation, and chromatography. These purification methods may be combined and carried out in two or more kinds.

[0067] In the production method of the present embodiment, the higher the conversion rate of the raw material, the better, and it is preferably 50 mol% or more, more preferably 80 mol% or more. The ideal upper limit is 100 mol%.

[0068] In the production method of the present embodiment, the higher the yield of the alkyl furan carboxylic acid ester, the better, and it is preferably 3% or more, more preferably 10% or more, and even more preferably 30% or more. The ideal upper limit is 100 mol%.

[0069] In the production method of the present embodiment, salts are usually not generated as by-products. Therefore, the obtained alkyl furan carboxylic acid ester is preferably used for various applications. In particular, the alkyl furan carboxylic acid ester obtained by the production method of the present embodiment is preferably used as various industrial materials and their raw materials.

Examples

[0070] The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. When the measuring instruments used in the examples are difficult to obtain due to being obsolete, etc., measurements can be carried out using other instruments having equivalent performance.

[0071] Raw materials <Substrate> MFF: Methylfurfural, manufactured by Fujifilm Wako Pure Chemical Corporation, 133 - 11771 CMF: Chloromethylfurfural, manufactured by Toronto Research Chemicals Inc, product number C369220 PrFF: Isopropylfurfural, manufactured by Matrix Scientific, 14497 - 27 - 9 <Solvent> Methanol: manufactured by Fujifilm Wako Pure Chemical Corporation, 137 - 01823 Toluene: manufactured by Fujifilm Wako Pure Chemical Corporation, 204 - 01866 THF: Tetrahydrofuran, manufactured by Fujifilm Wako Pure Chemical Corporation, 206 - 00483 <Base> Na2CO3: manufactured by Fujifilm Wako Pure Chemical Corporation, 199 - 01585 DBU: 1,8 - Diazabicyclo[5.4.0]undec - 7 - ene, manufactured by Tokyo Chemical Industry Co., Ltd., D1270 TEA: manufactured by Fujifilm Wako Pure Chemical Corporation, 208 - 02643 NaOH: manufactured by Fujifilm Wako Pure Chemical Corporation, 194 - 18865 NaOMe: manufactured by Tokyo Chemical Industry Co., Ltd., S0485 K2CO3: manufactured by Fujifilm Wako Pure Chemical Corporation, 162 - 03495 <Nucleophile> Methanol: manufactured by Fujifilm Wako Pure Chemical Corporation, 137 - 01823 PrOH: Normal propyl alcohol, manufactured by Tokyo Chemical Industry Co., Ltd., P0491

[0072] <Catalyst> Cat - 1: Sigma - Aldrich, 708607 - 1G, manufactured by Tokyo Chemical Industry Co., Ltd., D3962 Using Gaussian16, the stable structure of the catalyst molecule in methanol was obtained by the SMD method, and the pKa calculated from the free energy is 24.1.

Chemical formula

[0073] Example 1 <Production of Methyl Fluorate> 0.11 g (1 mmol) of MFF, 1 g of methanol, 0.07 g (0.3 eq, 0.3 mmol) of Cat-1, and 0.031 g (0.3 eq, 0.3 mmol) of sodium carbonate were charged into a 25 mL flask in this order. The mixture was stirred at 30 °C for 20 hours. After completion of the reaction, it was analyzed by GC and quantified by the absolute calibration curve method. The GC analysis was carried out under the following conditions. Apparatus GC-2014 manufactured by Shimadzu Corporation Column HP-5 (60 m * 0.25 mm, film thickness: 0.25 μm) Carrier gas Helium, 1 mL / min constant flow Oven 50 °C (5 min hold) - at 20 °C / min - 320 °C (15 min hold) Inlet 320 °C, Split (20:1), septum purge flow rate: 3 mL / min Injection volume 1 μL Note that the amount of the nucleophile indicates the total amount of methanol as the nucleophile when methanol is used as the solvent.

[0074] Examples 2 to 14, Comparative Examples 1 to 7 In Example 1, changes were made as shown in Tables 1 to 3, and the others were carried out in the same manner. The results are shown in Tables 1 to 3.

[0075]

Table 1

[0076]

Table 2

[0077]

Table 3

[0078] In Tables 1 to 3 above, base / cat indicates the molar ratio of the base to the catalyst. In the production method of the present invention, alkyl furan carboxylic acid ester was obtained in a high yield (Examples 1 to 10). On the other hand, when the amount of the effective catalyst was less than 0.005 mol (Comparative Examples 1, 2, 4, 7), the yield was low. Further, when the molar ratio of the base / catalyst was less than 0.08 (Comparative Examples 1 to 4, 7), the yield was also low. Furthermore, when the substrate was CMF (Comparative Examples 5, 6), the yield was also low. Furthermore, as is clear from the comparison of Examples 1 to 3 and the comparison of Examples 4 to 7, by setting the molar ratio of the base / catalyst to 5.0 or less, and further 3.0 or less, a higher yield can be achieved and the amount of the base used can be reduced.

Claims

1. A method for producing an alkyl furan carboxylate, which comprises performing a redox reaction between an alkyl furan aldehyde and a compound represented by A-OH (wherein A is an organic group having 1 to 10 carbon atoms) in the presence of an N-heterocyclic carbene catalyst, a base and a solvent, wherein the effective catalyst amount is 0.005 mol or more per 1 mol of the alkyl furan aldehyde, and the molar ratio of the base / catalyst is 0.08 or more. A method for producing an alkyl furan carboxylate.

2. The method for producing an alkyl furan carboxylate according to claim 1, wherein the molar ratio of the base / catalyst is 0.08 or more and 20.0 or less.

3. The method for producing an alkyl furan carboxylate according to claim 1 or 2, wherein the base contains at least one of diazabicycloundecene, sodium carbonate, sodium hydroxide, triethylamine, sodium methoxide, and potassium carbonate.

4. The method for producing an alkyl furan carboxylate according to any one of claims 1 to 3, wherein the effective catalyst amount is 0.01 mol or more per 1 mol of the alkyl furan aldehyde.

5. The method for producing an alkyl furan carboxylate according to any one of claims 1 to 4, wherein the molar ratio of the base / catalyst is 0.5 or more.

6. The method for producing an alkyl furan carboxylate according to any one of claims 1 to 5, wherein the N-heterocyclic carbene catalyst has a stable structure of the catalyst molecule in methanol determined by the SMD method using Gaussian 16, and the pKa calculated from the free energy is 33.0 or less.

7. The method for producing an alkyl furan carboxylate according to claim 6, wherein the pKa of the N-heterocyclic carbene catalyst is 20.0 or more.

8. The method for producing an alkyl furan carboxylate according to any one of claims 1 to 7, wherein the N-heterocyclic carbene catalyst contains at least one selected from the group consisting of triazolium, imidazolinium, imidazolium and thiazolium.

9. The method for producing an alkyl furan carboxylate according to any one of claims 1 to 8, wherein the N-heterocyclic carbene catalyst contains at least one of the catalysts represented by the following formula (C). 【Chemical 1】 (In formula (C), R C1 and R C2 each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, a heteroaryl group having 4 to 16 carbon atoms, a halogenated alkyl group having 1 to 12 carbon atoms, a halogenated aryl group having 6 to 18 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms. Z represents -S- or -NR c3 -. X represents a methine group (=CR C5 -), a nitrogen atom (=N-), or a methylene group (-CR C6 2 -). When X is a methine group or a nitrogen atom, the dashed line in the formula represents a double bond, and when X is a methylene group, the dashed line in the formula represents a single bond. In the formula, R C3 , R C5 and R C6 each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 2 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an acyl group having 2 to 12 carbon atoms, a hydroxy group, a carboxy group, or a halogen atom. Y - represents a counter anion. R C2 and R C3 , R C2 and R C5 , R C2 and R C6 may each be bonded or condensed to each other to form a ring.)

10. The method for producing an alkyl furancarboxylate according to claim 9, wherein the catalyst represented by the formula (C) contains at least one catalyst represented by the formula (C4). 【Chemical 2】 (In formula (C4), R 13 represents a group synonymous with R C1 . R 23 represents a group synonymous with R C2 . R 33 represents a group synonymous with R C3 . Y - represents a counter anion. R 23 and R 33 may each be bonded or condensed with each other to form a ring.)

11. The method for producing an alkyl furancarboxylate according to any one of claims 1 to 10, wherein the alkyl furanaldehyde is a compound represented by the formula (F1). [Chemical Formula 3] (In the formula (F1), R is an alkyl group having 1 to 10 carbon atoms.)

12. The method for producing an alkyl furancarboxylate according to any one of claims 1 to 11, wherein the alkyl furancarboxylate is a compound represented by the formula (F2). 【Chemical Formula 4】 (In the formula (F2), R is an alkyl group having 1 to 10 carbon atoms, and A is an organic group having 1 to 10 carbon atoms.)

13. The method for producing an alkyl furancarboxylate according to any one of claims 1 to 12, wherein in the compound represented by A-OH, A is an alkyl group having 1 to 5 carbon atoms.

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