JP7617610B2 - Method for producing phenyl esters - Google Patents

Description

The present invention relates to a method for producing a phenyl ester from a phenol and an aromatic carboxylic acid, and a catalyst used in the phenyl esterification reaction.

The reaction to synthesize phenyl esters is known as an important reaction for constructing the main structures in the production of various chemical products such as electronic materials, pharmaceuticals, and agricultural chemicals.
Generally, the reaction of directly converting phenol and aromatic carboxylic acid into a phenyl ester by dehydration has low reactivity, and therefore requires the addition of an additive or catalyst to dramatically improve the reactivity.

For example, a method for producing phenyl esters is known in which a carboxylic acid and a chloroformate are mixed in the presence of a base and then phenol is added (Patent Document 1). Alternatively, a method for producing phenyl esters is also known in which various sulfonic acids are added to a carboxylic acid and then phenol is allowed to react with the mixture (Patent Document 1).
However, these methods require the addition of bases or strong acids into the reaction vessel, which causes problems in the production process such as corrosion of the vessel. In addition, because the methods use additives such as chloroformates in the same amount as the raw materials, they generate large amounts of by-products derived from the additives as well as the target compound. Therefore, a lot of energy is required for the purification process of the product, and the disposal of the by-products from the purification process is also time-consuming and costly.

As a method for producing phenyl esters with fewer additives, a method for producing phenyl esters by combining boric acid with a mineral acid such as sulfuric acid has been reported (Non-Patent Document 1).Furthermore, a method for producing phenyl esters from carboxylic acids and phenols by combining sulfuric acid, boric acid, and dialkylmalonic acid is known (Patent Document 2).
However, these methods also use sulfuric acid, which corrodes the production vessel and requires complicated post-treatment of the strong acid, and therefore cannot be said to be industrially useful.

A method for producing phenyl esters that does not use a base or strong acid is known, which involves the reaction of an acid anhydride with phenol using scandium triflate (Non-Patent Document 2). However, this method has problems such as the cost of using compounds derived from scandium metal and the large amount of by-products generated by using a dehydrating agent, making it an industrially disadvantageous method.

JP 2006-342150 A JP 2011-105667 A

Tetrahedron. Lett. 1971, 37, 3453 J. Org. Chem. 1996, 61, 4560

As such, conventional reactions using strong acids, bases, or metal complexes have issues in terms of both energy conservation and quality, such as corrosion of containers and disposal of by-product waste.

Furthermore, because additives are added in large proportions to the raw materials, there are issues from both the perspectives of energy conservation and quality, such as the cost of removing them and the risk of product deterioration and reduced yields due to their inclusion in the product as impurities.

The present invention has been made in view of the above circumstances, and aims to provide a method for efficiently synthesizing phenyl esters by direct dehydration from phenol and aromatic carboxylic acid under relatively mild reaction conditions by using an ion exchange resin instead of a strong acid and in the coexistence of a boron-containing catalyst such as boric acid or an alkoxyborane under metal-free conditions, and a phenyl esterification catalyst that can efficiently synthesize phenyl esters by direct dehydration from phenol and aromatic carboxylic acid under relatively mild reaction conditions without using a strong acid.

The present invention has the following aspects.
[1] A method for directly producing a phenyl ester from a phenol and an aromatic carboxylic acid by dehydration, comprising the steps of:
A method for producing a phenyl ester, comprising contacting the two organic compounds in the presence of a catalyst containing an ion exchange resin and a boron compound.
[2] The method for producing a phenyl ester according to [1], wherein the ion exchange resin is made of a polymer having a sulfonic acid group on its surface.
[3] The method for producing a phenyl ester according to [1] or [2], wherein the boron compound is selected from boric acid or an alkoxyborane.
[4] The method for producing a phenyl ester according to any one of [1] to [3], wherein, among the boric acid or alkoxyborane, a boron compound represented by the following formula (i) is used:

（式（ｉ）中、Ｒ^１は、アルキル基、アリール基、水酸基もしくはアルコキシ基である。
式（ｉ）中、Ｒ^２及びＲ^３は、それぞれ独立に水素原子、アルキル基、アリール基もしくは水酸基である。また、Ｒ^２及びＲ^３は、互いに結合して環を形成してもよい。ただし、式（ｉ）中、Ｒ^２又はＲ^３のいずれか一方が水素原子であるか、または、Ｒ^２及びＲ^３が互いに結合して環を形成する場合には、Ｒ^１は水酸基である。）
〔５〕 前記触媒に含まれるホウ素化合物の量が、フェノール類または芳香族カルボン酸のいずれか少ない方の基質１ミリモルに対して１～４００ｍｇの範囲であり、
前記触媒に含まれるホウ素化合物の量が、基質の総質量に対して０．０１～２０質量％である、〔１〕～〔４〕のいずれかに記載のフェニルエステルの製造方法。
〔６〕 前記芳香族カルボン酸が下記式（１）に示す化合物であり、前記フェノール類が下記式（２）に示す化合物である、〔１〕～〔５〕のいずれかに記載のフェニルエステルの製造方法。

（式（１）中、Ｒ^４～Ｒ^７、及びＲ^８は、それぞれ独立に、水素原子、アルキル基、アルコキシ基、又はニトロ基を示す。これらの基はさらに、アルキル基、アリール基又はハロゲン原子等の置換基を有していてもよい。また、Ｒ^４～Ｒ^７、及びＲ^８から選ばれる二か所が互いに結合して環を形成してもよい。）

（式（２）中、Ｒ^９～Ｒ^１２、及びＲ^１３は、それぞれ独立に、水素原子、アルキル基、アルコキシ基、又はニトロ基を示す。これらの基はさらに、アルキル基、アリール基又はハロゲン原子等の置換基を有していてもよい。また、Ｒ^９～Ｒ^１２、及びＲ^１３から選ばれる二か所が互いに結合して環を形成してもよい。）
〔７〕フェノールと芳香族カルボン酸からフェニルエステルを合成する際に、脱水を伴いながら直接的に合成するための触媒であって、イオン交換樹脂とホウ素化合物を構成要素として含むことを特徴とする、フェニルエステル化触媒。
〔８〕前記イオン交換樹脂が、スルホン酸基を含有する強酸性のイオン交換樹脂からなる、〔７〕に記載のフェニルエステル化触媒。
〔９〕前記ホウ素化合物が、ホウ酸またはアルコキシボランから選ばれる、〔７〕又は〔８〕に記載のフェニルエステル化触媒。
〔１０〕前記ホウ酸またはアルコキシボランのうち、特に、下記式（ｉ）で表されるホウ素化合物を用いる、〔７〕～〔９〕のいずれかに記載のフェニルエステル化触媒。

In formula (i), R ¹ is an alkyl group, an aryl group, a hydroxyl group or an alkoxy group.
In formula (i), ^R2 and ^R3 are each independently a hydrogen atom, an alkyl group, an aryl group, or a hydroxyl group. ^R2 and ^R3 may be bonded to each other to form a ring. However, in formula (i), when either ^R2 or ^R3 is a hydrogen atom, or ^R2 and ^R3 are bonded to each other to form a ring, ^R1 is a hydroxyl group.
[5] The amount of the boron compound contained in the catalyst is in the range of 1 to 400 mg per 1 mmol of the substrate, which is the smaller of a phenol or an aromatic carboxylic acid;
The method for producing a phenyl ester according to any one of [1] to [4], wherein the amount of the boron compound contained in the catalyst is 0.01 to 20 mass% based on the total mass of the substrate.
[6] The method for producing a phenyl ester according to any one of [1] to [5], wherein the aromatic carboxylic acid is a compound represented by the following formula (1), and the phenol is a compound represented by the following formula (2):

(In formula (1), R ⁴ to R ⁷ and R ⁸ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a nitro group. These groups may further have a substituent such as an alkyl group, an aryl group, or a halogen atom. In addition, two positions selected from R ⁴ to R ⁷ and R ⁸ may be bonded to each other to form a ring.)

(In formula (2), R ⁹ to R ¹² and R ¹³ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a nitro group. These groups may further have a substituent such as an alkyl group, an aryl group, or a halogen atom. In addition, two positions selected from R ⁹ to R ¹² and R ¹³ may be bonded to each other to form a ring.)
[7] A phenyl esterification catalyst for directly synthesizing a phenyl ester from a phenol and an aromatic carboxylic acid while accompanying dehydration, the catalyst comprising an ion exchange resin and a boron compound as components.
[8] The phenyl esterification catalyst according to [7], wherein the ion exchange resin is a strongly acidic ion exchange resin containing a sulfonic acid group.
[9] The phenyl esterification catalyst according to [7] or [8], wherein the boron compound is selected from boric acid or an alkoxyborane.
[10] The phenyl esterification catalyst according to any one of [7] to [9], which uses, among the boric acid or alkoxyborane, a boron compound represented by the following formula (i):

（式（ｉ）中、Ｒ^１は、アルキル基、アリール基、水酸基もしくはアルコキシ基である。
式（ｉ）中、Ｒ^２及びＲ^３は、それぞれ独立に水素原子、アルキル基、アリール基もしくは水酸基である。また、Ｒ^２及びＲ^３は、互いに結合して環を形成してもよい。ただし、式（ｉ）中、Ｒ^２又はＲ^３のいずれか一方が水素原子であるか、または、Ｒ^２及びＲ^３が互いに結合して環を形成する場合には、Ｒ^１は水酸基である。）

In formula (i), R ¹ is an alkyl group, an aryl group, a hydroxyl group or an alkoxy group.
In formula (i), ^R2 and ^R3 are each independently a hydrogen atom, an alkyl group, an aryl group, or a hydroxyl group. ^R2 and ^R3 may be bonded to each other to form a ring. However, in formula (i), when either ^R2 or ^R3 is a hydrogen atom, or ^R2 and ^R3 are bonded to each other to form a ring, ^R1 is a hydroxyl group.

According to the present invention, a method for efficiently producing aromatic carboxylic acid phenyl esters from phenols and aromatic carboxylic acids with dehydration under relatively mild reaction conditions without the coexistence of additives such as strong acids, using a catalyst containing an ion exchange resin and a boron compound as components, and a catalyst containing an ion exchange resin and a boron compound as components that can efficiently produce aromatic carboxylic acid phenyl esters from phenols and aromatic carboxylic acids with dehydration under relatively mild reaction conditions without the coexistence of additives, can be provided.

FIG. 1 is a diagram showing one embodiment of a method for producing a phenyl ester of the present invention using a catalyst containing an ion exchange resin and a boron compound as components.

The present invention will be described in detail below. The materials and the like exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately modified and implemented within the scope of the present invention.
In this specification, the use of "to" indicating a range of values means that the values before and after it are included as the lower limit and upper limit.

The method for producing a phenyl ester of the present invention is a method for producing a phenyl ester by dehydration from a phenol and an aromatic carboxylic acid. Hereinafter, the phenol and the aromatic carboxylic acid are also referred to as "substrates".
In one embodiment of the method for producing a phenyl ester of the present invention, a substrate is reacted under dehydrating conditions using a batch reactor in the presence of a catalyst composed of an ion exchange resin and a boron compound (hereinafter also referred to as an "esterification catalyst") to produce phenyl esters at a predetermined reaction temperature.

<Esterification catalyst>
The esterification catalyst in the present invention is composed of an ion exchange resin and a boron compound. Even without the coexistence of an additive, the substrate can be efficiently converted to a phenyl ester through a dehydration reaction. In addition, since the ion exchange resin and the boron compound do not decompose before or after the reaction, they can be reused by filtering and recovering the solution after the reaction.

Ion exchange resins are easy to use, and are polymer resins with a basic skeleton of styrene with sulfonic acid groups arranged on the surface, and are stable and easy to recover and reuse. Examples of such polymers include ion exchange resins for sulfonic acid group-containing catalysts, and among them, ion exchange resins for strongly acidic sulfonic acid group-containing catalysts. Examples of such resins include Amberlyst15DRY and Amberlyst15JWET manufactured by Organo Corporation. As catalog products, Amberlyst15DRY and Amberlyst15JWET both have a total exchange capacity of 1 or more when wet, and 4 or more per dry resin. The total exchange capacity is determined by actually passing ions through the resin and titrating the amount of exchange. Since resins are susceptible to thermal decomposition at temperatures above 120°C, it is desirable to set the reaction conditions so that the reaction temperature does not exceed 120°C.

Various boron compounds can be used, from boric acid to alkyl-substituted boric acids and aryl-substituted boric acids, as long as they have one boron-hydroxyl group structure. It is believed that aromatic carboxylic acids and boron compounds first react to produce boric acid esters, which then react with phenol to produce phenyl esters. Therefore, it is believed that boron compounds in which the boron atom is directly substituted with alkyl or aryl groups rather than hydroxyl or alkoxy groups contribute more to improving catalytic activity.

An example of such a boron compound is the boron compound represented by the following formula (i):

In formula (i), R ¹ is an alkyl group, an aryl group, a hydroxyl group or an alkoxy group.
In formula (i), ^R2 and ^R3 are each independently a hydrogen atom, an alkyl group, an aryl group, or a hydroxyl group. ^R2 and ^R3 may be bonded to each other to form a ring. However, in formula (i), when either ^R2 or ^R3 is a hydrogen atom, or ^R2 and ^R3 are bonded to each other to form a ring, ^R1 is a hydroxyl group.

In ^R1 , examples of the alkyl group include linear or branched alkyl groups having 1 to 15 carbon atoms. Specific examples include a methyl group, an ethyl group, a propyl group, and an n-octyl group. The alkyl group may have a substituent such as an aryl group or a halogen atom.
Examples of the aryl group include monocyclic, polycyclic, or fused ring aromatic hydrocarbon groups having 6 to 20 carbon atoms, and preferably 6 to 14 carbon atoms. Specific examples include a phenyl group, a tolyl group, a xylyl group, anisyl group, a nitrophenyl group, a naphthyl group, a methylnaphthyl group, anthryl group, a phenanthryl group, and a biphenyl group. The aryl group may have a substituent such as an alkyl group or a halogen atom.
Examples of the alkoxy group include a methoxy group, an ethoxy group, a t-butoxy group, etc. The alkoxy group may have a substituent such as an alkyl group or a halogen atom.

In ^R2 and ^R3 , the alkyl group may be, for example, a linear or branched alkyl group having 1 to 15 carbon atoms. Specific examples include a methyl group, an ethyl group, a propyl group, and an n-octyl group. The alkyl group may have a substituent such as an aryl group or a halogen atom.
Examples of the aryl group include monocyclic, polycyclic, or fused ring aromatic hydrocarbon groups having 6 to 20 carbon atoms, and preferably 6 to 14 carbon atoms. Specific examples include a phenyl group, a tolyl group, a xylyl group, anisyl group, a nitrophenyl group, a naphthyl group, a methylnaphthyl group, anthryl group, a phenanthryl group, and a biphenyl group. The aryl group may have a substituent such as an alkyl group or a halogen atom.

The ring formed by ^R2 and ^R3 bonding to each other and the carbon atoms to which ^R2 and ^R3 are bonded may be an aromatic ring or an alicyclic ring. Examples of the aromatic ring include a monocyclic, polycyclic, or fused aromatic hydrocarbon ring having 6 to 20 carbon atoms, preferably 6 to 14 carbon atoms. Examples of the alicyclic ring include a monocyclic, polycyclic, or fused saturated hydrocarbon ring having 3 to 10 carbon atoms.
In a preferred embodiment, the boron compound is phenylboronic acid, boric acid, or isopropylboronic acid. Two or more kinds of boron compounds may be used in combination.

The esterification catalyst can be prepared by mixing the ion exchange resin and the boron compound in a solvent. The amount of the ion exchange resin and the boron compound used in preparing the esterification catalyst may be within a certain range relative to the substrate, as described below. A wide range of solvents can be used for preparing the esterification catalyst, including aromatic compounds such as toluene and xylene, aliphatic compounds such as octane and heptane, and ketones such as isobutyl methyl ketone. Solvents that do not decompose under the conditions of the ester synthesis reaction and are in a liquid state under the reaction conditions of the ester synthesis reaction can be preferably used. The solvent is preferably 0.1 to 1000 times, and more preferably 1 to 100 times, the total mass of the substrate (the total mass of the phenols and the aromatic carboxylic acid) in mass ratio so that it can be used as a liquid medium in the esterification reaction described below. The solution containing the esterification catalyst obtained by mixing the ion exchange resin and the boron compound in the solvent can be used as it is as a reaction solution for producing phenyl esters.

<Substrate>
The substrates in the production method of the present invention are phenols and aromatic carboxylic acids. The aromatic carboxylic acids are not particularly limited as long as they can produce phenyl esters in the production method of the present invention. The phenols are also not particularly limited as long as they are allenols having various substituents.
Examples of the substrate include a compound represented by the following formula (1) (hereinafter also referred to as "compound (1)"), a compound represented by the following formula (2) (hereinafter also referred to as "compound (2)"), and other compounds (compound 1) having a carboxylic acid attached to an aromatic ring, and arenol compounds (compound 2) having various substituents attached to an aromatic ring.

In formula (1) and formula (2), R ⁴ to R ¹² and R ¹³ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a nitro group. These groups may further have a substituent such as an alkyl group, an aryl group, or a halogen atom.
In formula (1), two positions selected from R ⁴ to R ⁷ and R ⁸ may be bonded to each other to form a ring.
In formula (2), two positions selected from R ⁹ to R ¹² and R ¹³ may be bonded to each other to form a ring.

In formula (1) and formula (2), examples of the alkyl group which may have a substituent in R ⁴ to R ¹² and R ¹³ include linear or branched alkyl groups having 1 to 15 carbon atoms. Specific examples include a methyl group, an ethyl group, a propyl group, and an n-octyl group.

In formula (1) and formula (2), the alkoxy group which may have a substituent in R ⁴ to R ¹² and R ¹³ includes, for example, a linear or branched alkyl group having 1 to 15 carbon atoms. Specific examples include a methoxy group, an ethoxy group, an i-propyl group, and a t-butyl group.

Specific examples of the substrate include aromatic carboxylic acids such as benzoic acid, 4-methylbenzoic acid, 4-methoxybenzoic acid, and 3-methylbenzoic acid.
Examples of phenols include phenol, 4-methylphenol, 4-methoxyphenol, 4-bromophenol, and 4-nitrophenol.

<Esterification>
By mixing the substrates in the presence of an esterification catalyst, the esterification reaction proceeds with dehydration of the substrates.
An example of a method for contacting substrates together under dehydrating conditions is to place the substrates together and a liquid medium in a container and stir them in air.

The amount of the esterification catalyst used for the ion exchange resin is, for example, 1 to 400 mg, preferably 10 to 200 mg, more preferably 50 to 150 mg per millimole of the phenols or aromatic carboxylic acid used in the same amount. Usually, it is preferable to use the same amounts of the phenols and aromatic carboxylic acid as the substrates. However, the ratio of the phenols to the aromatic carboxylic acid is not limited as long as a phenyl ester can be produced. When the amount of either the phenols or the aromatic carboxylic acid used is small, the amount of the esterification catalyst used may be within the above range per millimole of the smaller substrate.
When the amount of the esterification catalyst used is equal to or greater than the lower limit of the above range, the esterification reaction of the substrate is more likely to proceed. When the amount of the esterification catalyst used exceeds the upper limit of the above range, the added catalyst may hinder stirring, resulting in a decrease in catalytic activity.

The amount of the esterification catalyst used, in the case of a boron compound, is, for example, 0.01 to 20 mass %, preferably 0.01 to 10 mass %, more preferably 0.05 to 5 mass %, relative to the total mass (100 mass %) of the substrate.
When the amount of the esterification catalyst used is equal to or greater than the lower limit of the above range, the esterification reaction of the substrate is more likely to proceed. When the amount of the esterification catalyst used exceeds the upper limit of the above range, the added catalyst may hinder stirring, resulting in a decrease in catalytic activity.

As the liquid medium, all common organic solvents can be used, for example, toluene, octane, etc. These liquid media may be used alone or in combination of two or more kinds.
The amount of the liquid medium used is preferably 0.1 to 1000 times, and more preferably 1 to 100 times, the total mass of the substrate, in terms of mass ratio.

There are no particular limitations on the reaction conditions for the esterification reaction, but the reaction temperature is preferably 0 to 150°C, more preferably 80 to 120°C.
The reaction time depends on the amount of catalyst used, the reaction temperature, etc. and cannot be generally determined, but is usually within the range of 1 to 40 hours, preferably within the range of 6 to 18 hours.

It is preferable to carry out the esterification reaction in the absence of additives. By carrying out the esterification reaction in the absence of additives, the purity of the product is increased. In addition, the amount of energy input during purification after the reaction can be reduced.

Because the esterification reaction is known to be an equilibrium reaction involving dehydration, it is desirable to design a reactor that incorporates a mechanism for promoting dehydration from the reaction system, such as a Dean-Stark reaction. For example, it is effective to place a desiccant such as a molecular sieve at the top of the reaction vessel and incorporate a mechanism for promoting dehydration during reflux into the reactor together with the catalyst.

After the reaction is complete, the resulting product (e.g., phenyl ester compound) can be extracted by conventional methods such as distillation, chromatographic separation, recrystallization, and sublimation.

<Product>
As described above, by esterifying the substrate phenol and aromatic carboxylic acid with dehydration in the presence of a liquid medium under specific reaction conditions, a phenyl ester compound as shown in the following formula (3) can be obtained.

In formula (3), R ⁴ to R ¹² and R ¹³ each have the same meaning as defined above.

Specific examples of the resulting phenyl ester compounds include phenyl benzoate, (4-methyl)phenyl benzoate, (3-methyl)phenyl benzoate, (2-methyl)phenyl benzoate, (4-methoxy)phenyl benzoate, (4-bromo)phenyl benzoate, (4-chloro)phenyl benzoate, and (4-nitro)phenyl benzoate.

In the present invention described above, by using the above-mentioned esterification catalyst, phenol can be efficiently esterified under relatively mild conditions without the coexistence of an additive, and a phenyl ester compound can be obtained in high yield without producing by-products accompanied by dehydration.
In addition, the above-mentioned esterification catalyst is an ion exchange resin and a boron compound, so that it does not decompose during esterification and can be reused.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.
The conversion rate and yield in the esterification were calculated from the results of gas chromatography using the following formulas.
Conversion rate (%)=(1-number of moles of remaining raw material/number of moles of raw material used)×100
Yield (%) = (number of moles of target compound/number of moles of raw material used) x 100

（実施例１）
３０φの試験管に撹拌子を入れ、イオン交換樹脂としてAmberlyst 15DRY（オルガノ製）１１４ｍｇとホウ素化合物としてフェニルボロン酸３０．５ｍｇを入れ、さらに基質としてフェノール（東京化成工業株式会社製）を９４１mg、安息香酸（東京化成工業株式会社製）を１２２１ｍｇ入れ、液状媒体としてトルエン（ナカライテスク株式会社製）を５ｍＬ加え、モレキュラーシーブ４Aを備えた還流管に接続し、１気圧のアルゴン下１２０℃で１６時間撹拌した。その後、内部標準としてn-テトラデカン（ナカライテスク株式会社製）を３７３．３ｍｇ加え、ガスクロマトグラフィー測定を行った。その結果、転化率は７７％、安息香酸フェニルの収率は７２％であり、その他に副生成物は検出されなかった。 The chemical reaction formula in one embodiment of the method for producing a phenyl ester of the present invention is shown below.

Example 1
A stirrer was placed in a 30φ test tube, 114 mg of Amberlyst 15DRY (Organo) was placed as an ion exchange resin, and 30.5 mg of phenylboronic acid was placed as a boron compound. 941 mg of phenol (Tokyo Chemical Industry Co., Ltd.) and 1221 mg of benzoic acid (Tokyo Chemical Industry Co., Ltd.) were placed as substrates, and 5 mL of toluene (Nacalai Tesque Co., Ltd.) was added as a liquid medium. The tube was connected to a reflux tube equipped with a molecular sieve 4A and stirred at 120 °C under argon at 1 atmosphere for 16 hours. Then, 373.3 mg of n-tetradecane (Nacalai Tesque Co., Ltd.) was added as an internal standard, and gas chromatography measurement was performed. As a result, the conversion rate was 77%, the yield of phenyl benzoate was 72%, and no other by-products were detected.

Example 2
Except for using boric acid instead of phenylboronic acid, the reaction was carried out under the same conditions as in Example 1. As a result, the conversion was 82% and the yield of phenyl benzoate was 74%.

Example 3
The reaction was carried out under the same conditions as in Example 1, except that Amberlyst 15JWET was used instead of Amberlyst 15DRY as the ion exchange resin. As a result, the conversion rate was 67%, and the yield of phenyl benzoate was 63%. From this result, the reactivity of the ion exchange resin is not affected whether or not it contains moisture within the resin.

(Comparative Example 1)
Of the catalysts, no ion exchange resin was used, and the reaction was carried out under the same conditions as in Example 1. As a result, the conversion rate was 0%.

(Comparative Example 2)
Except for using cyclopentyl methyl ether instead of toluene as the solvent, the reaction was carried out under the same conditions as in Example 1. As a result, no phenyl benzoate was detected.

(Comparative Example 3)
The reaction was carried out under the same conditions as in Example 1, except that the reaction temperature was 80° C. As a result, the conversion was 10% and the yield of phenyl benzoate was 8%.

The results of Examples 1 to 3 and Comparative Examples 1 to 3, in which phenol was used as the substrate, are shown in Table 1.

Table 2 shows Examples 4 to 9 in which esterification reactions using substrates in which various substituents were substituted on the aromatic ring of phenol were carried out under the same conditions as in Example 1, except that various substituted phenols were used instead of phenol.

(Example 10)
Except for using 4-acetamidophenol instead of phenol, the reaction was carried out under the same conditions as in Example 1. As a result, the conversion was 10% and the yield of the target ester was 5%.

(Comparative Example 4)
The reaction was carried out under the same conditions as in Example 10, except that no boron compound was used as a catalyst. As a result, the conversion rate was 0%.

Comparison of Examples 1 to 3 with Example 10 and Comparative Examples 1 to 3 with Comparative Example 4 confirmed that phenyl esters can be obtained in high yields by using a catalyst containing an optimized ion exchange resin and a boron compound and by carrying out an esterification reaction in a reaction vessel and at a reaction temperature that promotes dehydration.
The results of Examples 4 to 9 confirmed that the present catalyst system was also effective for various substituted phenols and substituted aromatic carboxylic acids.

The reaction to synthesize phenyl esters is known as an important reaction for constructing the main structure in the manufacture of various chemical products such as electronic materials, pharmaceuticals, and agricultural chemicals. According to the present invention, phenyl ester compounds can be efficiently produced using phenol and aromatic carboxylic acid as raw materials, with only water as a by-product, and with dehydration by simple catalyst mixing. Therefore, the present invention can be widely used, mainly in the fields of intermediates for pharmaceuticals and agricultural chemicals, and raw materials for resins.

Claims (5)

A method for directly producing a phenyl ester from a phenol and an aromatic carboxylic acid by dehydration, comprising the steps of:
The aromatic carboxylic acid is a compound represented by the following formula (1), and the phenol is a compound represented by the following formula (2),
A method for producing a phenyl ester, comprising contacting the phenol with an aromatic carboxylic acid in the presence of a catalyst containing a strongly acidic ion exchange resin for sulfonic acid group-containing catalysts and a boron compound selected from boric acid or an alkoxyborane, and toluene, and reacting the phenol with the aromatic carboxylic acid at a temperature higher than 80°C and not higher than 120°C.

(In formula (1), R ⁴ to R ⁷ and R ⁸ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a nitro group. These groups may further have a substituent such as an alkyl group, an aryl group, or a halogen atom. In addition, two positions selected from R ⁴ to R ⁷ and R ⁸ may be bonded to each other to form a ring.)

(In formula (2), R ⁹ to R ¹² and R ¹³ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a nitro group. These groups may further have a substituent such as an alkyl group, an aryl group, or a halogen atom . In addition, two positions selected from R ⁹ to R ¹² and R ¹³ may be bonded to each other to form a ring.) The method for producing phenyl esters according to claim 1, wherein the ion exchange resin is made of a polymer having sulfonic acid groups on its surface. The method for producing a phenyl ester according to claim 1 or 2, wherein a boron compound represented by the following formula (i) is used as the boric acid or alkoxyborane:

In formula (i), R ¹ is an alkyl group, an aryl group, a hydroxyl group or an alkoxy group.
In formula (i), ^R2 and ^R3 are each independently a hydrogen atom, an alkyl group, an aryl group, or a hydroxyl group. ^R2 and ^R3 may be bonded to each other to form a ring. However, in formula (i), when either ^R2 or ^R3 is a hydrogen atom, or ^R2 and ^R3 are bonded to each other to form a ring, ^R1 is a hydroxyl group. The method for producing a phenyl ester according to any one of claims 1 to 3, wherein the aromatic carboxylic acid is benzoic acid and the phenol is phenol. the amount of the boron compound contained in the catalyst is in the range of 1 to 400 mg per 1 mmol of the substrate, which is the smaller of a phenol or an aromatic carboxylic acid;
The method for producing a phenyl ester according to any one of claims 1 to 4, wherein the amount of the boron compound contained in the catalyst is 0.01 to 20% by mass based on the total mass of the substrate.

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