JP7501838B2 - Method for producing ester compound - Google Patents

Description

The present invention relates to a method for producing an ester compound.

Ester compounds are used as intermediate raw materials for solvents, fragrances, emulsifiers, moisturizers, pharmaceuticals, etc. Recently, lactate esters, which are ester compounds, have been attracting attention as solvents for resists and paints, and as cleaning agents.

US Pat. No. 5,999,333 discloses a method for the carbonylation of vinyl acetate by reacting vinyl acetate with carbon monoxide in the presence of a source of hydroxyl groups and a catalyst system that combines (a) a Group VIIIB metal or a compound thereof, and (b) a specific bidentate phosphine.
Patent Document 2 discloses a method for producing a propionic acid ester derivative by reacting a substituted vinyl compound with an alcohol compound and carbon monoxide in the presence of a Group 8 metal compound of the periodic table, a phosphorus ligand and a polymeric sulfonic acid compound.
Patent Document 3 discloses a method for producing a propionic acid ester derivative by reacting an olefinically unsaturated compound with an alcohol and carbon monoxide in the presence of at least one of a Group 10 metal compound and a neutral promoter.

Patent Document 4 describes a method for producing a 2-hydroxycarboxylic acid, which includes (a) a step of reacting an enol ester with carbon monoxide and a hydroxyl compound in the presence of a palladium catalyst and a solvent to obtain a carbonyl ester, and (b) a step of hydrolyzing the carbonyl ester with an acid catalyst to obtain a 2-hydroxycarboxylic acid. Patent Document 4 describes vinyl acetate as the enol ester, dichlorobis(triphenylphosphine)palladium(II) (PdCl ₂ (PPh ₃ ) ₂ ) as the palladium catalyst, methanol as the hydroxyl compound, and lactic acid as the 2-hydroxycarboxylic acid.

Patent document 5 describes a method for producing a 2-hydroxy acid, which comprises the steps of (1) reacting an enolic acylate with carbon monoxide and a hydroxyl compound to produce an acyloxy ester or a hydroxy ester, or both, and (2) hydrolyzing the product of (1) to produce a 2-hydroxy acid.

Furthermore, Non-Patent Document 1 discloses a method in which an olefin compound (enol ester) is reacted with an alcohol (methanol) and carbon monoxide using a palladium complex catalyst in the presence of a basic cocatalyst such as a pyridine derivative.
Non-Patent Document 2 discloses a methoxycarbonylation reaction of vinyl acetate using a palladium catalyst and a monodentate ligand such as triphenylphosphine.

JP 2006-508162 A JP 2005-247703 A JP 2006-225282 A US Patent Application Publication No. 2005/0143600 Japanese Patent Application Laid-Open No. 60-149544

Bulletin of the Chemical Society of Japan, 1996, Vol. 69, pp. 1337-1345 ARKIVOC, 2012, (iii) pp. 66-75

However, the conventional methods for producing ester compounds have been insufficient in yield and selectivity of the ester compounds, and therefore there is a demand for a method for producing an ester compound with high yield and high selectivity.
The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a production method capable of producing an ester compound with high yield and high selectivity.

Means for Solving the Problems In order to solve the above problems, the present inventors have focused on a catalyst used in producing an ester compound by reacting a vinyl carboxylate, an alcohol, and carbon monoxide, and have conducted extensive research.
As a result, it was found that it would be sufficient to use a catalyst containing a compound having at least one element selected from the group consisting of elements in Groups 9 and 10 of the periodic table, and a specific organic phosphine ligand having a biphenyl group.
Furthermore, the present inventors have confirmed that an ester compound can be produced with high yield and high selectivity by reacting a specific vinyl carboxylate, a specific alcohol, and carbon monoxide in the presence of the above catalyst, and have arrived at the present invention.
That is, the present invention relates to the following.

[1] A method for producing an ester compound represented by general formula (1), comprising the steps of:
The method includes a reaction step of reacting a vinyl carboxylate represented by general formula (2), a primary or secondary alcohol represented by general formula (3), and carbon monoxide in the presence of a catalyst,
The catalyst contains a compound having at least one element selected from the group consisting of elements in Groups 9 and 10 of the periodic table, and an organic phosphine ligand represented by the following general formula (4):

（式（１）において、Ｒ^１は、水素原子、炭素原子数１～８のアルキル基、シクロヘキシル基またはフェニル基を表す。Ｒ^２は、炭素原子数１～１０の炭化水素基であり、一部または全部に脂環または芳香環を有していてもよい炭化水素基を表す。）
（式（２）において、Ｒ^１は式（１）におけるＲ^１と同じである。）
（式（３）において、Ｒ^２は式（１）におけるＲ^２と同じである。）
（式（４）において、Ｒ^３、Ｒ^４は、炭素原子数１～６のアルキル基、炭素原子数６～９のシクロアルキル基、炭素原子数６～９のアリール基であり、同一であってもよいし、異なっていてもよい。Ｒ^５～Ｒ^９は、水素原子、炭素原子数１～４のアルキル基、炭素原子数１～４のアルコキシ基、炭素原子数２～８のジアルキルアミノ基であり、全て同一であってもよいし、一部または全部が異なっていてもよい。）

(In formula (1), R ¹ represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cyclohexyl group, or a phenyl group. R ² represents a hydrocarbon group having 1 to 10 carbon atoms, which may have an alicyclic or aromatic ring in part or in whole.)
(In formula (2), R ¹ is the same as R ¹ in formula (1).)
(In formula (3), ^R2 is the same as ^R2 in formula (1).)
(In formula (4), R ³ and R ⁴ are an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 6 to 9 carbon atoms, or an aryl group having 6 to 9 carbon atoms, and may be the same or different. R ⁵ to R ⁹ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a dialkylamino group having 2 to 8 carbon atoms, and may all be the same or some or all may be different.)

[2] The method for producing an ester compound according to [1], wherein the vinyl carboxylate represented by the general formula (2) is vinyl acetate.
[3] The method for producing an ester compound according to [1] or [2], wherein the primary or secondary alcohol represented by the general formula (3) is any one selected from methanol, ethanol, and 1-butanol.
[4] The method for producing an ester compound according to [3], wherein the primary or secondary alcohol represented by the general formula (3) is ethanol.

[5] The method for producing an ester compound according to any one of [1] to [4], wherein the element of Group 9 of the periodic table is at least one selected from Co, Rh, and Ir, and the element of Group 10 of the periodic table is at least one selected from Ni, Pd, and Pt.
[6] The method for producing an ester compound according to [5], wherein the element of Group 10 of the periodic table is Pd.
[7] The method for producing an ester compound according to any one of [1] to [6], wherein, in general formula (4), R ³ and R ⁴ are cyclohexyl groups, R ⁵ and R ⁹ are methoxy groups, and R ⁶ to R ⁸ are hydrogen atoms.

[8] The method for producing an ester compound according to any one of [1] to [7], wherein the catalyst contains an acidic compound.
[9] The method for producing an ester compound according to [8], wherein the acidic compound is at least one selected from the group consisting of alkylsulfonic acids, ammonium salts of alkylsulfonic acids, pyridinium salts of alkylsulfonic acids, arylsulfonic acids, ammonium salts of arylsulfonic acids, and pyridinium salts of arylsulfonic acids.
[10] The method for producing an ester compound according to any one of [1] to [9], wherein the catalyst contains a nitrogen atom-containing heterocyclic compound.
[11] The method for producing an ester compound according to [10], wherein the nitrogen atom-containing heterocyclic compound is at least one selected from pyridine and picoline.

[12] A method for producing an ester compound according to any one of [1] to [11], comprising charging a vinyl carboxylate represented by the general formula (2), a primary or secondary alcohol represented by the general formula (3), the catalyst, and a solvent, and carrying out the reaction in the reaction step in a reaction vessel in a carbon monoxide gas atmosphere.

In the method for producing an ester compound of the present invention, a vinyl carboxylate represented by general formula (2), a primary or secondary alcohol represented by general formula (3), and carbon monoxide are reacted in the presence of a catalyst containing a compound having at least one element selected from the elements of Groups 9 and 10 of the Periodic Table and an organic phosphine ligand represented by general formula (4). This allows the production of an ester compound with high yield and high selectivity.

The method for producing an ester compound of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments.
"Ester compounds"
The method for producing an ester compound according to the present embodiment is a method for producing an ester compound represented by the following general formula (1).

（式（１）において、Ｒ^１は、水素原子、炭素原子数１～８のアルキル基、シクロヘキシル基またはフェニル基を表す。Ｒ^２は、炭素原子数１～１０の炭化水素基であり、一部または全部に脂環または芳香環を有していてもよい炭化水素基を表す。）

(In formula (1), R ¹ represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cyclohexyl group, or a phenyl group. R ² represents a hydrocarbon group having 1 to 10 carbon atoms, which may have an alicyclic or aromatic ring in part or in whole.)

In the ester compound represented by the general formula (1), R ¹ represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cyclohexyl group, or a phenyl group. R ¹ is preferably a methyl group, since it can be produced with a higher yield and higher selectivity. In addition, an ester compound in which R ¹ in the formula (1) is a methyl group is useful and preferable as a precursor raw material of a lactate ester that can be synthesized from vinyl acetate, which is easily available industrially as a vinyl ester.
In the ester compound represented by the general formula (1), ^R2 is a hydrocarbon group having 1 to 10 carbon atoms, which may have an alicyclic or aromatic ring in part or in whole. ^R2 is preferably any one selected from a methyl group, an ethyl group, and an n-butyl group, and more preferably a methyl group or an ethyl group, since this allows production with a higher yield and higher selectivity.

The method for producing an ester compound of the present embodiment includes a reaction step of reacting a vinyl carboxylate, a primary or secondary alcohol, and carbon monoxide in the presence of a catalyst.
In the method for producing an ester compound of the present embodiment, it is preferable to carry out the reaction (alkoxycarbonylation reaction) in the reaction step in a reaction vessel containing a vinyl carboxylate, a primary or secondary alcohol, a catalyst, and a solvent and having a carbon monoxide gas atmosphere.

"Vinyl carboxylate"
In this embodiment, as the vinyl carboxylate, a vinyl carboxylate represented by the following general formula (2) is used.

（式（２）において、Ｒ^１は式（１）におけるＲ^１と同じである。）

(In formula (2), R ¹ is the same as R ¹ in formula (1).)

R ¹ in the vinyl carboxylate represented by the general formula (2) is the same as R ¹ in the formula (1). Specifically, examples of the vinyl carboxylate represented by the general formula (2) include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl cyclohexane carboxylate, and vinyl benzoate. When an ester compound represented by the general formula (1) in which R ¹ is a methyl group is produced using the method for producing an ester compound of this embodiment, vinyl acetate in which R ¹ is a methyl group is used as the vinyl carboxylate represented by the general formula (2). Vinyl acetate is industrially available at low cost and is therefore preferred.

"Primary or secondary alcohol"
In this embodiment, as the primary or secondary alcohol, a primary or secondary alcohol represented by the following general formula (3) is used.
^R2OH (3)
(In formula (3), ^R2 is the same as ^R2 in formula (1).)

^R2 in the primary or secondary alcohol represented by the general formula (3) is the same as ^R2 in the formula (1). Specific examples of the primary or secondary alcohol represented by the general formula (3) include methanol, ethanol, 1-propanol, isopropanol, 1-butanol, isobutyl alcohol, sec-butyl alcohol, 1-hexanol, 1-octanol, 2-ethylhexanol, cyclohexanemethanol, and benzyl alcohol.

When an ester compound represented by general formula (1) in which R ² is any one selected from a methyl group, an ethyl group, and an n-butyl group is produced using the method for producing an ester compound of this embodiment, any one selected from methanol in which R ² is a methyl group, ethanol in which R ² is an ethyl group, and 1-butanol in which R ² is an n-butyl group is used as the primary or secondary alcohol represented by general formula (3). As the primary or secondary alcohol represented by general formula (3), it is preferable to use methanol or ethanol, and it is more preferable to use ethanol. Methanol, ethanol, or 1-butanol are preferable because they have high reactivity with the vinyl carboxylate represented by general formula (2).

In the method for producing an ester compound of this embodiment, the molar ratio of the amount of primary or secondary alcohol used (charged amount) to the amount of vinyl carboxylate used (charged amount) is preferably 1:0.5 to 1:100, more preferably 1:1 to 1:10, and even more preferably 1:1.2 to 1:5, in order to produce an ester compound with a higher yield and higher selectivity.

"Carbon monoxide"
In this embodiment, it is preferable to use a gas containing carbon monoxide as carbon monoxide. The gas containing carbon monoxide may be a gas containing only carbon monoxide, or may be a gas containing inert gas such as nitrogen or argon, hydrogen gas, etc. in addition to carbon monoxide. It is preferable that the gas containing carbon monoxide does not contain oxidizing gas such as air or oxygen.

The amount of carbon monoxide used during the reaction is, for example, preferably in the range of 0.05 to 50 MPa, more preferably in the range of 0.1 to 30 MPa, and even more preferably in the range of 1 to 6 MPa, in which a reaction solution containing vinyl carboxylate and a primary or secondary alcohol is charged and the reaction vessel is made into a gas atmosphere containing carbon monoxide. It is particularly preferable to carry out the reaction while replenishing the carbon monoxide consumed by the reaction so that the partial pressure of carbon monoxide in the reaction vessel during the reaction is maintained within the range of 1 to 6 MPa. If the partial pressure of carbon monoxide in the reaction vessel during the reaction is 0.05 MPa or more, the reaction proceeds smoothly. In order to promote the reaction, it is preferable that the partial pressure of carbon monoxide in the reaction vessel during the reaction is high. However, in order to make the partial pressure of carbon monoxide during the reaction exceed 50 MPa, it is necessary to use an expensive device. By making the partial pressure of carbon monoxide during the reaction 50 MPa or less, an ester compound can be produced using an industrially suitable device and method.

"catalyst"
The catalyst used in the method for producing an ester compound of this embodiment contains a compound having at least one element selected from Group 9 and Group 10 elements of the periodic table, and an organic phosphine ligand represented by the following general formula (4): The organic phosphine ligand represented by general formula (4) is coordinated to an element contained in the compound having at least one element selected from Group 9 and Group 10 elements of the periodic table.

（式（４）において、Ｒ^３、Ｒ^４は、炭素原子数１～６のアルキル基、炭素原子数６～９のシクロアルキル基、炭素原子数６～９のアリール基であり、同一であってもよいし、異なっていてもよい。Ｒ^５～Ｒ^９は、水素原子、炭素原子数１～４のアルキル基、炭素原子数１～４のアルコキシ基、炭素原子数２～８のジアルキルアミノ基であり、全て同一であってもよいし、一部または全部が異なっていてもよい。）

(In formula (4), R ³ and R ⁴ are an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 6 to 9 carbon atoms, or an aryl group having 6 to 9 carbon atoms, and may be the same or different. R ⁵ to R ⁹ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a dialkylamino group having 2 to 8 carbon atoms, and may all be the same or some or all may be different.)

Examples of compounds containing at least one element selected from Group 9 elements of the periodic table include compounds containing at least one element selected from Co, Rh, and Ir, and it is particularly preferable to use a compound containing rhodium. Examples of compounds containing rhodium include rhodium(III) chloride and/or rhodium(III) nitrate.

The compound having at least one element selected from the periodic table group 10 elements can be, for example, a compound containing at least one element selected from Ni, Pd, and Pt, and it is particularly preferable to use a compound containing palladium.The compound containing palladium can be, for example, at least one zero- or divalent palladium compound selected from palladium chloride (II), palladium nitrate (II), palladium sulfate (II), palladium acetate (II), bis(acetylacetonato)palladium (II) (Pd(acac) ₂ ), tris(dibenzylideneacetone)dipalladium (0) (Pd ₂ (dba) ₃ ), and dipalladium (0) _tris (dibenzylideneacetone)chloroform (Pd ₂ (dba) 3.CHCl ₃ ).

Among these compounds containing at least one element selected from the elements of Groups 9 and 10 of the periodic table, it is preferable to use a compound containing palladium in terms of reaction rate and selectivity, and it is particularly preferable to use palladium(II) chloride or bis(acetylacetonato)palladium(II) (Pd(acac) ₂ ).
The compound having at least one element selected from the group consisting of elements in Groups 9 and 10 of the periodic table contained in the catalyst may be of only one type, or of two or more types.

The amount of the compound having at least one element selected from Groups 9 and 10 of the periodic table is preferably 0.00001 to 0.2 molar parts, more preferably 0.0001 to 0.1 molar parts, and even more preferably 0.001 to 0.05 molar parts, per 1 molar part of the vinyl carboxylate represented by the general formula (2). When the amount of the compound having at least one element selected from Groups 9 and 10 of the periodic table is 0.00001 molar parts or more per 1 molar part of the vinyl carboxylate represented by the general formula (2), the concentration of the reactive species of the catalyst (hydride complex, etc.) can be ensured. Therefore, the alkoxycarbonylation reaction that produces the ester compound represented by the general formula (1) is effectively promoted. In addition, it is economically preferable that the amount of the compound having at least one element selected from Groups 9 and 10 of the periodic table is 0.2 molar parts or less.

In the organic phosphine ligand represented by the general formula (4), R ³ and R ⁴ are an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 6 to 9 carbon atoms, or an aryl group having 6 to 9 carbon atoms. R ³ and R ⁴ may be the same or different. R ³ and R ⁴ are preferably cyclohexyl groups, since this allows the ester compound to be produced in a higher yield and with a higher selectivity, and it is particularly preferred that both R ³ and R ⁴ are cyclohexyl groups.

R ⁵ to R ⁹ in the organic phosphine ligand represented by the general formula (4) are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a dialkylamino group having 2 to 8 carbon atoms. R ⁵ to R ⁹ may all be the same, or some or all of them may be different. In particular, it is preferable that R ⁵ and R ⁹ are methoxy groups and R ⁶ to R ⁸ are hydrogen atoms, since this enables the ester compound to be produced in a higher yield and with a higher selectivity.

Specific examples of the organic phosphine ligand represented by general formula (4) include the organic phosphine ligands represented by the following formulas (4-1) to (4-6).

（式（４－１）において、Ｃｙはシクロヘキシル基であり、Ｍｅはメチル基である。）

(In formula (4-1), Cy is a cyclohexyl group, and Me is a methyl group.)

（式（４－２）において、Ｃｙはシクロヘキシル基である。）

(In formula (4-2), Cy is a cyclohexyl group.)

（式（４－３）において、Ｃｙはシクロヘキシル基であり、Ｍｅはメチル基である。）

(In formula (4-3), Cy is a cyclohexyl group, and Me is a methyl group.)

（式（４－４）において、Ｃｙはシクロヘキシル基であり、ｉＰｒはイソプロピル基である。）

(In formula (4-4), Cy is a cyclohexyl group, and iPr is an isopropyl group.)

（式（４－５）において、Ｃｙはシクロヘキシル基である。）

(In formula (4-5), Cy is a cyclohexyl group.)

（式（４－６）において、Ｃｙはシクロヘキシル基であり、ｉＰｒはイソプロピル基である。）

(In formula (4-6), Cy is a cyclohexyl group, and iPr is an isopropyl group.)

As the organic phosphine ligand represented by general formula (4), among the organic phosphine ligands represented by formulae (4-1) to (4-6), it is particularly preferable to use an organic phosphine ligand represented by formula (4-1) in which R ³ and R ⁴ are cyclohexyl groups, R ⁵ and R ⁹ are methoxy groups, and R ⁶ to R ⁸ are hydrogen atoms in general formula (4), because this enables the production of an ester compound in a higher yield and with a higher selectivity.
The organophosphine ligand represented by the general formula (4) contained in the catalyst may be of one type or of two or more types.

The amount of the organic phosphine ligand represented by general formula (4) used is preferably 0.5 to 5 molar parts, more preferably 1 to 4 molar parts, and even more preferably 1.5 to 3 molar parts, per 1 molar part of the compound having at least one element selected from the elements of Groups 9 and 10 of the periodic table. When the amount of the organic phosphine ligand represented by general formula (4) used is 0.5 molar parts or more per 1 molar part of the compound having at least one element selected from the elements of Groups 9 and 10 of the periodic table, reactive species of the catalyst in which the organic phosphine is effectively coordinated are efficiently generated. As a result, the alkoxycarbonylation reaction is promoted, and the ester compound represented by general formula (1) is produced with a higher selectivity.

When the amount of the organic phosphine ligand represented by general formula (4) used is 5 molar parts or less per 1 molar part of the compound having at least one element selected from Group 9 and Group 10 elements of the periodic table, the reaction to produce the ester compound represented by general formula (1) can be effectively promoted. This is because, when there is too much organic phosphine ligand represented by general formula (4), it becomes difficult for carbon monoxide to be coordinated in the alkoxycarbonylation reaction to produce the ester compound represented by general formula (1), and this prevents the reaction rate of the alkoxycarbonylation reaction from slowing down.

The catalyst used in the method for producing an ester compound of the present embodiment preferably contains not only a compound having at least one element selected from Group 9 and Group 10 elements of the periodic table and an organic phosphine ligand represented by general formula (4), but also an acidic compound. In this specification, the term "acidic compound" refers to a Brønsted acid, a salt of a Brønsted acid, or a Lewis acid. The Brønsted acid or a salt of a Brønsted acid is preferred.
Moreover, the catalyst used in this embodiment more preferably contains a nitrogen atom-containing heterocyclic compound.
In the present embodiment, when the acidic compound used as the catalyst is a compound having a nitrogen atom-containing heterocycle, the acidic compound can also serve as the nitrogen atom-containing heterocycle. An example of the acidic compound that also serves as the nitrogen atom-containing heterocycle is picolinic acid.

The catalyst contains an acidic compound, which promotes the alkoxycarbonylation reaction that produces the ester compound represented by general formula (1). The acidic compound used as the catalyst functions as a hydriding agent for at least one element selected from the elements of Groups 9 and 10 of the periodic table. This is presumably what promotes the alkoxycarbonylation reaction.

Examples of acidic compounds include hydrochloric acid, nitric acid, sulfuric acid, alkanoic acids having 2 to 12 carbon atoms, sulfonic acids such as methanesulfonic acid, chlorosulfonic acid, fluorosulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid, o-toluenesulfonic acid, m-toluenesulfonic acid, p-toluenesulfonic acid, t-butylsulfonic acid, and 2-hydroxypropanesulfonic acid, and their salts, sulfonated ion exchange resins, perhalogen acids such as perchloric acid, perfluorinated carboxylic acids such as trichloroacetic acid and trifluoroacetic acid, orthophosphoric acid, phosphonic acids such as benzenephosphonic acid, and esters of sulfonic acids such as dimethyl sulfate, methyl methanesulfonate, and methyl trifluoromethanesulfonate.

Among these, since the acidity is appropriate, it is preferable that the acidic compound is at least one selected from alkylsulfonic acid, ammonium salts of alkylsulfonic acid, pyridinium salts of alkylsulfonic acid, arylsulfonic acid, ammonium salts of arylsulfonic acid, and pyridinium salts of arylsulfonic acid, and in particular, p-toluenesulfonic acid is preferable.

If the acid strength of the catalyst is too strong, a side reaction is likely to occur between the raw material vinyl carboxylate represented by general formula (2) and the primary or secondary alcohol represented by general formula (3).If the acid strength of the catalyst is too weak, the effect of accelerating the reaction rate of the alkoxycarbonylation reaction that produces the ester compound represented by general formula (1) may be insufficient.
The catalyst may contain only one type of acidic compound, or two or more types of acidic compounds.

The amount of the acidic compound used is preferably in the range of 0.05 to 4 molar parts of acid sites (protons) per 1 molar part of the compound having at least one element selected from Groups 9 and 10 of the periodic table, more preferably 0.1 to 2 molar parts, and even more preferably 0.2 to 1 molar parts. When the acidic compound has 0.05 molar parts or more of acid sites per 1 molar part of the compound having at least one element selected from Groups 9 and 10 of the periodic table, reactive species of the catalyst (hydride complexes, etc.) are efficiently generated, and the alkoxycarbonylation reaction to generate the ester compound represented by general formula (1) is effectively promoted. In addition, when the acidic compound has 4 molar parts or less of acid sites per 1 molar part of the compound having at least one element selected from Groups 9 and 10 of the periodic table, side reactions in the alkoxycarbonylation reaction can be effectively suppressed.

In the method for producing an ester compound according to the present embodiment, when the catalyst contains a nitrogen-containing heterocyclic compound together with an acidic compound, the catalytic activity is improved, and the alkoxycarbonylation reaction that produces the ester compound represented by the general formula (1) is further promoted. This is presumed to be due to the following reasons. The nitrogen-containing heterocyclic compound has a nitrogen-containing heterocycle. Therefore, when the nitrogen-containing heterocyclic compound is contained in the catalyst together with the acidic compound, the acidity of the catalyst is easily adjusted to a range in which the alkoxycarbonylation reaction is promoted. In addition, for example, when a chloride (palladium chloride, etc.) of at least one element selected from Groups 9 and 10 of the periodic table is used as the compound having at least one element selected from Groups 9 and 10 of the periodic table, and a basic compound is used as the nitrogen-containing heterocyclic compound, the decomposition of the chloride (palladium chloride, etc.) is suppressed, and hydrochloric acid generated by the decomposition of the chloride is neutralized, suppressing side reactions. As a result, it is presumed that the catalyst is activated and the alkoxycarbonylation reaction is promoted.

Examples of the nitrogen atom-containing heterocyclic compound include pyridine, picoline, imidazole, pyrazole, oxazole, etc. Among these, the nitrogen atom-containing heterocyclic compound is preferably at least one selected from pyridine and picoline, and more preferably pyridine, since the ester compound represented by the general formula (1) can be produced in a higher yield and with a higher selectivity.
The catalyst may contain only one type of nitrogen atom-containing heterocyclic compound, or two or more types of nitrogen atom-containing heterocyclic compounds.

The amount of the nitrogen atom-containing heterocyclic compound used is preferably 0.1 to 50 molar parts, more preferably 1 to 30 molar parts, and even more preferably 3 to 20 molar parts, per molar part of the compound having at least one element selected from Groups 9 and 10 of the periodic table. When the amount of the nitrogen atom-containing heterocyclic compound used is 0.1 molar parts or more per molar part of the compound having at least one element selected from Groups 9 and 10 of the periodic table, the acidity of the catalyst is likely to be within a range in which the alkoxycarbonylation reaction is promoted, and the ester compound represented by general formula (1) is likely to be produced with high selectivity. In addition, it is preferable that the amount used is 50 molar parts or less per molar part of the compound having at least one element selected from Groups 9 and 10 of the periodic table, since side reactions are suppressed.

"solvent"
As the solvent used in the method for producing an ester compound of the present embodiment, it is preferable to use a chemical species that does not participate in the reaction between vinyl carboxylate, a primary or secondary alcohol, and carbon monoxide. Examples of such solvents include tetrahydrofuran, dioxane, acetone, methyl ethyl ketone, cyclohexanone, ethyl acetate, n-propyl acetate, n-butyl acetate, n-heptane, acetonitrile, toluene, xylene, N-methylpyrrolidone, γ-butyrolactone, N,N-dimethylformamide, and N,N-dimethylacetamide.

Among these solvents, it is preferable to use one or more selected from tetrahydrofuran, acetone, ethyl acetate, toluene, and xylene, since this allows the ester compound represented by general formula (1) to be produced in higher yield and with higher selectivity, and it is particularly preferable to use toluene, because of its solubility in the catalyst and ease of separation from the product.

The amount of solvent used is preferably in the range of 0.05 to 20 mol/L, more preferably 0.1 to 10 mol/L, and even more preferably 0.5 to 5 mol/L, such that the concentration of vinyl carboxylate represented by general formula (2) in the reaction solution is in the range of 0.05 mol/L or more, and the concentration of vinyl carboxylate in the reaction solution is likely to be in the range in which the alkoxycarbonylation reaction is promoted. It is preferable that the concentration of vinyl carboxylate represented by general formula (2) in the reaction solution is 20 mol/L or less, since this makes it easier to ensure a substrate concentration that allows the reaction to proceed smoothly.

In the method for producing an ester compound of this embodiment, if the primary or secondary alcohol represented by general formula (3) is a liquid at the reaction temperature of the alkoxycarbonyl reaction that produces the ester compound represented by general formula (1) and also serves as a solvent capable of dissolving the ester compound represented by general formula (1) produced by the alkoxycarbonyl reaction, a solvent may not be used. Examples of such primary or secondary alcohols include methanol, ethanol, 1-propanol, isopropanol, 1-butanol, isobutyl alcohol, sec-butanol, 1-hexanol, 2-ethylhexanol, and benzyl alcohol.

In the method for producing an ester compound of the present embodiment, the reaction conditions in the reaction step can be appropriately determined depending on the type of the ester compound represented by general formula (1) to be produced, etc., within a range in which the alkoxycarbonylation reaction of vinyl carboxylate, a primary or secondary alcohol, and carbon monoxide gas proceeds.
The reaction conditions preferably satisfy at least one of the following conditions: (a) reaction pressure, (b) reaction temperature, and (c) reaction time.

(a) Reaction Pressure The reaction step is preferably carried out at a carbon monoxide partial pressure in the reaction vessel of 0.05 to 50 MPa, more preferably 0.1 to 30 MPa, and even more preferably 1 to 6 MPa. By setting the carbon monoxide partial pressure in the reaction vessel to 0.05 to 50 MPa, the ester compound represented by the general formula (1) can be produced in a higher yield and with a higher selectivity.
(b) Reaction Temperature The reaction step is preferably carried out at a temperature in the reaction vessel of, for example, 60 to 140° C., more preferably 80 to 120° C. When the temperature in the reaction vessel is 60° C. or higher, the alkoxycarbonylation reaction that produces the ester compound represented by the general formula (1) is further promoted. When the temperature in the reaction vessel is 140° C. or lower, side reactions in the alkoxycarbonylation reaction can be suppressed, which is preferable.

(c) Reaction Time The reaction step is preferably carried out for, for example, 1 to 40 hours, and more preferably 10 to 20 hours. When the reaction time in the reaction step is 1 hour or more, the ester compound represented by general formula (1) can be produced in a higher yield and with a higher selectivity. When the reaction time in the reaction step is 40 hours or less, side reactions accompanying the production of the ester compound represented by general formula (1) can be suppressed.

The present invention will be described in more detail below with reference to examples and comparative examples. Note that the present invention is not limited to the following examples.

(Examples 1 to 8)
In a 40 mL stainless steel reaction vessel, a stirrer, PdCl ₂ (palladium chloride; manufactured by Soekawa Rikagaku Co., Ltd.; 3.0 mg, 17.01 μmol) as a catalyst compound having at least one element selected from Group 9 and Group 10 elements of the periodic table, organic phosphine ligands represented by formulas (4-1) to (4-6) (all manufactured by Aldrich Chemical Industry Co., Ltd.; 14.0 mg, 34.02 μmol) as catalysts, and PTSA (p-toluenesulfonic acid monohydrate: manufactured by Tokyo Chemical Industry Co., Ltd.; 1.3 mg, 6.723 μmol) as an acidic compound as catalyst were placed in the proportions shown in Table 1.

As the compounds shown in Table 1, the following were used.
MeOH (methanol; Fujifilm Wako Pure Chemical Industries, Ltd.)
EtOH (ethanol; Fujifilm Wako Pure Chemical Industries, Ltd.)
_PPh3 (triphenylphosphine; manufactured by Tokyo Chemical Industry Co., Ltd.)

In the reaction vessel containing these catalysts, under a nitrogen gas flow, vinyl acetate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.; 0.75 mL, 8.1 mmol) as the vinyl carboxylate, a primary or secondary alcohol (0.81 mL, 20 mmol) shown in Table 1, toluene (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.; 6.75 mL) as the solvent, and pyridine (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.; 0.0275 mL, 340.2 μmol) as the nitrogen atom-containing heterocyclic compound serving as the catalyst were added in the proportions shown in Table 1 to obtain a reaction solution.

The amount of palladium chloride used in Examples 1 to 8 was 0.002 parts by mol relative to 1 part by mol of vinyl acetate. The amount of organic phosphine ligand used was 2 parts by mol relative to 1 part by mol of palladium chloride. The amount of PTSA (p-toluenesulfonic acid monohydrate) used was 0.395 parts by mol of acid sites relative to 1 part by mol of palladium chloride. The amount of pyridine used was 20 parts by mol relative to 1 part by mol of palladium chloride.
The amount of toluene used was 0.83 liters per 1 mole of the primary or secondary alcohol (an amount that results in a vinyl acetate concentration of 1.2 mol/liter in the reaction liquid).

Next, the reaction vessel was pressurized and depressurized three times between atmospheric pressure and 1 MPa using carbon monoxide gas, and the gas in the reaction vessel was replaced with carbon monoxide gas. Thereafter, the pressure in the reaction vessel was adjusted to the pressure shown in Table 2 using carbon monoxide gas, and the reaction solution was reacted while stirring at the reaction temperature shown in Table 2 for the reaction time shown in Table 2 to produce an ester compound.

(Comparative Example 1)
A stirrer, PdCl ₂ (palladium chloride; manufactured by Soekawa Rikagaku Co., Ltd.; 0.80 mg, 4.455 μmol) as a catalyst compound having at least one element selected from Group 9 and Group 10 elements of the periodic table, 1,2-bis(di-tert-butylphosphinomethyl)benzene represented by the following formula (5) (manufactured by Sigma-Aldrich Japan LLC; 3.21 mg, 8.91 μmol) as an organic phosphine ligand as a catalyst, and methanesulfonic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.; 0.86 mg, 8.91 μmol) as an acidic compound as a catalyst were placed in a stainless steel reaction vessel having a capacity of 40 mL in the proportions shown in Table 1.

（式（５）において、ｔＢｕはtert－ブチル基である。）

(In formula (5), tBu is a tert-butyl group.)

Into the reaction vessel containing these catalysts, under a nitrogen gas flow, vinyl acetate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.; 0.75 mL, 8.1 mmol) as the vinyl carboxylate, a primary or secondary alcohol (4.5 mL, 111 mmol) shown in Table 1, and pyridine (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.; 0.0275 mL, 340.2 μmol) as the nitrogen atom-containing heterocyclic compound serving as the catalyst were placed in the proportions shown in Table 1 to obtain a reaction solution.
Next, the gas in the reaction vessel was replaced with carbon monoxide gas in the same manner as in Example 1. Thereafter, the pressure in the reaction vessel was adjusted to the pressure shown in Table 2 using carbon monoxide gas, and the reaction solution was reacted at the reaction temperature shown in Table 2 for the reaction time shown in Table 2 while being stirred to produce an ester compound.

(Comparative Example 2)
An ester compound was produced in the same manner as in Example 1, except that PPh ₃ (triphenylphosphine) was used as the organic phosphine ligand instead of the organic phosphine ligand represented by the formula (4-1).

For each of Examples 1 to 8 and Comparative Examples 1 and 2, the reaction liquid after the reaction was analyzed using gas chromatography (apparatus name: 6850GC, manufactured by Agilent Technologies, Inc.). Quantitative analysis of the raw materials, the target ester compound, and the by-products was performed by creating a calibration curve using diethylene glycol dimethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) as the internal standard substance.

As a result, it was confirmed that in Examples 1 to 6 and Comparative Examples 1 and 2, in which methanol was used as the primary or secondary alcohol, an ester compound in which R ¹ and R ² in formula (1) were methyl groups was produced as the target product. Also, in Examples 7 and 8, in which ethanol was used as the primary or secondary alcohol, it was confirmed that an ester compound in which R ¹ in formula (1) was a methyl group and R ² in formula (1) was an ethyl group was produced as the target product. The conversion rate of vinyl acetate, the yield of the target product, and the selectivity calculated from these values are shown in Table 2.

As shown in Table 2, in Examples 1 to 8, the target product was produced in a high yield of 35% or more and with a high selectivity of 60% or more.
In particular, in Examples 1 and 7 in which the organic phosphine ligand represented by the formula (4-1) was used as the organic phosphine ligand, the yield and selectivity were high.
Moreover, in Example 8, in which the reaction time was longer than that in Example 7, the yield was higher.

On the other hand, in Comparative Example 1 in which the compound represented by the formula (5) was used as the organic phosphine ligand, the selectivity of the target product was lower than those in Examples 1 to 7.
In Comparative Example 2 in which PPh ₃ (triphenylphosphine) was used as the organic phosphine ligand, the amount of the by-reaction product, which was an isomer (normal form) of the target product, was large, and the yield of the target product was low.

Claims (10)

A method for producing an ester compound represented by general formula (1), comprising the steps of:
The method includes a reaction step of reacting a vinyl carboxylate represented by general formula (2), a primary or secondary alcohol represented by general formula (3), and carbon monoxide in the presence of a catalyst,
The method for producing an ester compound, wherein the catalyst contains a compound having Pd and an organic phosphine ligand represented by the following general formula (4):

(In formula (1), R ¹ represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cyclohexyl group, or a phenyl group. R ² represents a hydrocarbon group having 1 to 10 carbon atoms, which may have an alicyclic or aromatic ring in part or in whole.)
(In formula (2), R ¹ is the same as R ¹ in formula (1).)
(In formula (3), ^R2 is the same as ^R2 in formula (1).)
(In formula (4), R ³ and R ⁴ are an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 6 to 9 carbon atoms, or an aryl group having 6 to 9 carbon atoms, and may be the same or different. R ⁵ to R ⁹ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a dialkylamino group having 2 to 8 carbon atoms, and may all be the same or some or all may be different.) The method for producing an ester compound according to claim 1, wherein the vinyl carboxylate represented by general formula (2) is vinyl acetate. The method for producing an ester compound according to claim 1 or 2, wherein the primary or secondary alcohol represented by general formula (3) is selected from methanol, ethanol, and 1-butanol. The method for producing an ester compound according to claim 3, wherein the primary or secondary alcohol represented by general formula (3) is ethanol. The method for producing an ester compound according to any one of claims 1 to 4 , wherein, in general formula (4), R ³ and R ⁴ are cyclohexyl groups, R ⁵ and R ⁹ are methoxy groups, and R ⁶ to R ⁸ are hydrogen atoms. The method for producing an ester compound according to any one of claims 1 to 5 , wherein the catalyst contains an acidic compound. The method for producing an ester compound according to claim 6, wherein the acidic compound is at least one selected from the group consisting of alkylsulfonic acids, ammonium salts of alkylsulfonic acids, pyridinium salts of alkylsulfonic acids, arylsulfonic acids, ammonium salts of arylsulfonic acids, and pyridinium salts of arylsulfonic acids. The method for producing an ester compound according to any one of claims 1 to 7 , wherein the catalyst comprises a nitrogen atom-containing heterocyclic compound. The method for producing an ester compound according to claim 8 , wherein the nitrogen atom-containing heterocyclic compound is at least one selected from pyridine and picoline. The method for producing an ester compound according to any one of claims 1 to 9, wherein the reaction in the reaction step is carried out in a reaction vessel in which the vinyl carboxylate represented by the general formula (2), the primary or secondary alcohol represented by the general formula ( 3 ), the catalyst, and a solvent are charged and an atmosphere of carbon monoxide gas is maintained.