JP2003192636A - Method for producing aromatic substituted alkyl ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an aromatic substituted alkyl ester with more improved production efficiency. <P>SOLUTION: This method for producing the aromatic substituted alkyl ester comprises reacting an alkyl-substituted aromatic compound with an aliphatic carboxylic acid and oxygen in the presence of a catalyst by using a mixture comprising the alkyl-substituted aromatic compound, the aliphatic carboxylic acid and water as a raw material. The mixture comprising the water in an amount of 0.01-5 mass% based on the alkyl-substituted aromatic compound, aliphatic carboxylic acid and water is used as the raw material. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an aromatic substituted alkyl ester.

[0002]

2. Description of the Related Art Aromatic substituted alkyl esters such as p-xylylene diacetate are used as raw materials for synthetic resins such as polyester resins, chemicals such as fragrances and solvents, or raw materials thereof.

As a method for producing an aromatic-substituted alkyl ester, generally known is a method in which an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen are reacted in the presence of a catalyst. In this production method, various oxidative esterification catalysts have been developed as catalysts in order to increase the production efficiency (for example, JP-A-63-174950, JP-A-62-273927, JP-A-8-). 231466).

[0004]

However, when the aromatic substituted alkyl ester is synthesized by the above reaction, the production efficiency may be lowered due to another problem even if these catalysts are used.

That is, when water is present in a system for producing an aromatic-substituted alkyl ester by reacting an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen (molecular oxygen) in the presence of a catalyst for oxidative esterification. The ester group of the product is hydrolyzed to produce an aromatic substituted alkyl alcohol and an aliphatic carboxylic acid. Further, the generated aromatic substituted alkyl alcohol is easily oxidized in an oxidizing atmosphere to produce an aromatic aldehyde or an aromatic carboxylic acid.

Since the hydrolysis is an equilibrium reaction, the more the content of water in the reaction solution is, the more the hydrolysis of the aromatic-substituted alkyl ester proceeds, and the aromatic-substituted alkyl alcohol is produced. Further, when the aromatic substituted alkyl alcohol decreases due to the generation of aromatic aldehyde or aromatic carboxylic acid by oxidation, hydrolysis of the aromatic substituted alkyl ester proceeds, and the yield of aromatic substituted alkyl ester further decreases.

Further, since the raw material alkyl-substituted aromatic compound has low solubility in water, when the water concentration in the reaction liquid becomes high, the reaction liquid may be separated into two phases, an aqueous phase and an organic phase. When the reaction solution is separated into two phases, the alkyl-substituted aromatic compound is mainly distributed to the organic phase and the aliphatic carboxylic acid is mainly distributed to the aqueous phase, so that the contact efficiency between the alkyl-substituted aromatic compound and the aliphatic carboxylic acid is lowered. The production amount of aromatic substituted alkyl ester is reduced.

Therefore, a main object of the present invention is to provide a method capable of producing an aromatic substituted alkyl ester more efficiently.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in view of the above problems, and as a result, in the oxidative esterification reaction, the content of water in the raw material or the water in the reaction solution was increased. The inventors have found that the above objects can be achieved by controlling the content, and have completed the present invention.

That is, the present invention relates to the following method for producing an aromatic substituted alkyl ester.

1. A mixture containing an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and water is used as a raw material, and an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen are reacted in the presence of a catalyst to produce an aromatic-substituted alkyl ester. A method, wherein a mixture in which the amount of water is 0.01 to 5 mass% with respect to the total of the alkyl-substituted aromatic compound, the aliphatic carboxylic acid and water is used as the raw material. For producing group-substituted alkyl ester.

2. Furthermore, an alkyl-substituted aromatic compound,
Item 1 above, which has a step of recycling at least an unreacted raw material and / or an intermediate reaction product among the components present in the reaction solution obtained by reacting an aliphatic carboxylic acid and oxygen into the reaction as a raw material. Manufacturing method.

3. A mixture containing an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and water is used as a raw material, and an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen are reacted in the presence of a catalyst to produce an aromatic-substituted alkyl ester. A method for producing an aromatic-substituted alkyl ester, which comprises reacting while extracting a part or all of water existing in a reaction solution to the outside of the reaction system.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing an aromatic-substituted alkyl ester according to the present invention uses a mixture containing an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and water as a raw material, and an alkyl-substituted aromatic compound in the presence of a catalyst. A method for producing an aromatic-substituted alkyl ester by reacting an aliphatic carboxylic acid and oxygen, wherein the amount of water relative to the alkyl-substituted aromatic compound, aliphatic carboxylic acid and water is used as the raw material. It is characterized by using a mixture of 0.01 to 5 mass%.

Further, the method for producing an aromatic-substituted alkyl ester of the present invention uses a mixture containing an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and water as a raw material, and in the presence of a catalyst, the alkyl-substituted aromatic compound, the fatty acid A method for producing an aromatic substituted alkyl ester by reacting an aromatic carboxylic acid and oxygen, characterized by reacting while extracting a part or all of water present in the reaction solution to the outside of the reaction system. Is.

(1) Raw Material The present invention is premised on a reaction system in which water is contained in the raw material.

The alkyl-substituted aromatic compound may be a compound in which at least one alkyl group is directly bonded to the aromatic ring.

Examples of the aromatic ring include hydrocarbon aromatic rings such as benzene ring and naphthalene ring, and heteroaromatic rings such as pyridine ring, furan ring and thiophene ring. In the present invention, a hydrocarbon aromatic ring (particularly a benzene ring) is preferable.

The alkyl group directly bonded to the aromatic ring is not particularly limited, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group and an isobutyl group. In the present invention, an alkyl group having 1 to 4 carbon atoms is preferable, and a methyl group is particularly preferable.

The alkyl-substituted aromatic compound may have, in addition to the alkyl group, a functional group which is inert to the oxidative esterification reaction in the production of the aromatic-substituted alkyl ester. For example, aryl group, hydroxyl group, halogen group,
Examples thereof include a nitro group, an amide group, an alkyloxy group, an aryloxy group, an alkylcarboxyl group, an arylcarboxyl group, an alkylcarbonyl group, an arylcarbonyl group, an alkylcarboxyalkyl group and an arylcarboxyalkyl group. Above all, it is desirable to have an alkylcarboxyalkyl group (particularly acetoxymethyl group), a hydroxyl group, and an alkylcarboxyl group (particularly acetoxyl group).

In the present invention, the alkyl-substituted aromatic compound is a compound in which at least one of the alkyl groups having 1 to 4 carbon atoms is directly bonded to the aromatic ring, and the substituent directly bonded to the aromatic ring is Those having two or more in total including an alkyl group are preferable.

In particular, a compound having two or more alkyl groups,
Alternatively, a compound having one or more alkyl groups and one or more functional groups selected from the group consisting of alkylcarboxylalkyl groups, hydroxyl groups and alkylcarboxyl groups is preferable.

Specific examples of the alkyl-substituted aromatic compound of the present invention include toluene, ethylbenzene, n-propylbenzene, isopropylbenzene, n-butylbenzene, sec-butylbenzene and trimethylbenzene.
Alkylbenzene; xylene, ethyltoluene, n-propyltoluene, isopropyltoluene, n-butyltoluene, sec-butyltoluene, etc., o-, m-, p-
Dialkylbenzenes; aryl-substituted alkylbenzenes such as 4,4′-dimethylbiphenyl; cresols, o
-, M-, p-hydroxy-substituted alkylbenzenes; o-, m-, p-halogen-substituted alkylbenzenes such as chlorotoluene; nitro group-substituted alkylbenzenes such as o-, m-, p-nitrotoluene; and methylaniline, such as o
-, M-, p-amino group-substituted alkylbenzene; o-, m-, p-amide group-substituted alkylbenzene such as methylbenzamide; o-, m-, p such as methylanisole
-Alkyloxy-substituted alkylbenzenes; o-, m-, p-aryloxy-substituted alkylbenzenes such as phenoxytoluene; o-, m-, p-carboxy such as tolyl acetate, tolyl propionate, tolyl butanoate and tolyl benzoate Substituted alkylbenzene (carboxylic acid tolyl ester); o-, m-, p-carbonyl substituted alkylbenzene such as methylacetophenone and methylbenzophenone; o-, m-, p- such as methylbenzylacetate
Besides carboxyalkyl-substituted alkylbenzene, methylnaphthalene, dimethylnaphthalene, dimethylpyridine and the like can be mentioned. These can be used alone or in combination of two or more. Among the alkyl-substituted aromatic compounds exemplified above, alkylbenzene, dialkylbenzene and carboxyalkyl-substituted alkylbenzene are more preferable, and o-, m-, p-xylene and o-, m-, p
-Methylbenzyl acetate is particularly preferred.

The aliphatic carboxylic acid is not particularly limited. In the present invention, it is particularly desirable to use a monocarboxylic acid. Specific examples thereof include aliphatic carboxylic acids such as acetic acid, propionic acid and butanoic acid. Acetic acid is particularly preferable.

The aromatic-substituted alkyl ester which is the product of the present invention is an aromatic-substituted alkyl ester produced by carrying out an oxidative esterification reaction of an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen in the presence of a catalyst. It is an ester. Specifically, it is a compound containing an ester in a form in which a carboxyl group of an aliphatic carboxylic acid and a carbon of an alkyl group of an alkyl-substituted aromatic compound are directly bonded to an aromatic ring. More specifically, for example, when toluene and propionic acid are used as raw materials, the aromatic substituted alkyl ester obtained is benzyl propionate.
Further, for example, when p-xylene and acetic acid are used as raw materials, the aromatic substituted alkyl ester obtained is p-methylbenzyl acetate and p-xylylene diacetate.

In the present invention, the amount of water contained in the raw material is 0.01 to 5 mass% with respect to the total amount of the above-mentioned alkyl-substituted aromatic compound, aliphatic carboxylic acid and water as the raw material.
Is. The lower limit and the upper limit of the amount of water can be set individually. That is, the lower limit is preferably 0.1% by mass, more preferably 0.5% by mass, even more preferably 1% by mass, most preferably 1.2% by mass, and the upper limit is preferably 4.5%. It is mass%, and more preferably 4 mass%.

The amount of water contained in the reaction solution is 0.01 to 5% by mass based on the total amount of the alkyl-substituted aromatic compound, the aliphatic carboxylic acid and the water in the reaction solution. The lower limit and the upper limit of the amount of water can be set individually. That is, the lower limit is preferably 0.1% by mass, more preferably 0.5% by mass, even more preferably 1% by mass, most preferably 1.2% by mass, and the upper limit of the amount of water is
It is preferably 4.5% by mass, more preferably 4% by mass.

When the amount of water exceeds 5% by mass, hydrolysis of the aromatic-substituted alkyl ester is promoted, which is not preferable. However, the amount of water contained in the raw material is 5% by mass.
Even if it exceeds, when the reaction is carried out while maintaining the amount of water in the reaction solution at 0.01 to 5% by mass, the hydrolysis of the aromatic substituted alkyl ester is not promoted.

Water is by-produced in the oxidative esterification reaction. In addition, water may be generated by a side reaction. Therefore, by extracting a part or all of the water contained in the reaction solution out of the reaction system and suppressing or reducing the increase in the amount of water in the reaction system, the hydrolysis is suppressed and the aromatic substituted alkyl ester. The yield of can be improved.

As a method of reducing the amount of water in the reaction solution, there are a method of extracting water from the system and a method of separating water from the reaction solution in the system. As a method of extracting water to the outside of the system, there is a method of extracting water by entraining water in the reaction liquid with a supply gas (for example, air, nitrogen gas, oxygen gas, argon gas). In this case, the removal of water becomes more efficient by adding components that form the lowest azeotrope with water (eg toluene, xylene, cyclohexane). Also,
As a method of separating water from the reaction solution in the system, there is a method of adsorbing water to an adsorbent. Examples of the adsorbent include molecular sieve and sodium sulfate.

The reaction is carried out while extracting water out of the system, and the amount of water present in the reaction solution at the end of the reaction is such that the total amount of alkyl-substituted aromatic compound, aliphatic carboxylic acid and water in the reaction solution is It is preferable to extract water so that the amount is 0.01 to 5% by mass.

Further, the amount of water present in the reaction solution during the reaction is adjusted to 0.01 to 5% by mass with respect to the total amount of the alkyl-substituted aromatic compound, the aliphatic carboxylic acid and the water in the reaction solution. It is preferable to drain water. The time for maintaining the amount of water within the above range is preferably 50% or more, more preferably 70% or more, of the total reaction time. When the amount of water contained in the raw material before the reaction is 0.01 to 5% by mass, it is most preferable to extract the water so as to maintain the above range for the entire reaction time.

(2) Recycling step In the production method of the present invention, further, at least unreacted raw material among the components present in the reaction solution obtained by reacting the alkyl-substituted aromatic compound, the aliphatic carboxylic acid and oxygen. And / or a step of recycling the intermediate reaction product as a raw material (recycling step) may be included.

The intermediate reaction product means that when, for example, a compound having two or more alkyl groups is used as the alkyl-substituted aromatic compound, a part of the alkyl group reacts to form an ester and the unreacted alkyl group is It refers to the remaining compound.

Among the components present in the reaction solution, at least the unreacted raw material and / or the intermediate reaction product can be reused as the above raw material. Improving production efficiency by recycling these components (effective use of raw materials)
Can be achieved more effectively. Examples of unreacted raw materials include unreacted alkyl-substituted aromatic compounds and unreacted aliphatic carboxylic acids. In addition, examples of the intermediate reaction product (intermediate) include aromatic substituted alkyl esters having at least one unreacted alkyl group remaining.

When the starting material contains an alkyl-substituted aromatic compound having two alkyl groups, the reaction solution contains an aromatic ester (full ester) in which all the alkyl groups are oxidatively esterified, and an alkyl group. May be partially oxidized to form an aromatic ester (half ester) in which an unreacted alkyl group remains. Half ester is useful as a raw material for resins and the like, but when the intended product is a full ester or when the production ratio of the full ester and the half ester is smaller than the intended production ratio, the half ester is The half ester can be effectively used by recycling the raw material to the reaction system again.

The aromatic substituted alkyl ester having at least one alkyl group, which is an intermediate reaction product, can be recycled and used as a raw material. In this case, the content ratio of the aromatic substituted alkyl ester having at least one alkyl group in the raw material is as follows: alkyl substituted aromatic compound: aromatic substituted alkyl ester = 1: 10 to 10: 1 (weight ratio ), Especially 1: 5
It is preferably 5: 1. By setting it in such a range, the amount of aromatic carboxylic acid produced can be suppressed, and the productivity can be further enhanced.

The components to be recycled can be separated and recovered from the reaction solution by using a general technique such as distillation (batch distillation, continuous distillation), extraction and the like.

In the present invention, when the above components are reused, it is preferable to have a step (removal step) of removing a part or all of water in the reaction solution. By the removal step, the amount of water in the raw material containing the recycled component can be efficiently controlled. This removing step may be performed before it is reused as a raw material, and can be performed, for example, before the recycling step, after the recycling step, or simultaneously with the recycling step.

As the starting alkyl-substituted aromatic compound,
When a raw material such as toluene or xylene that has low compatibility with water and is azeotropic with water is used, an azeotropic mixture of an alkyl-substituted aromatic compound and water is extracted from the top of the tower by distillation, and 2
The amount of water can be easily reduced by recycling only the phase-separated organic phase.

In the case of recovering unreacted aliphatic carboxylic acid, when the utility cost is too high to recover by distillation, it can be recovered by adding water to the reaction solution to extract the aliphatic carboxylic acid. . Since aromatic-substituted alkyl esters have low solubility in water, when water is added to the reaction solution, an aqueous phase mainly composed of water and an aliphatic carboxylic acid, an aromatic-substituted alkyl ester and an unreacted alkyl-substituted aromatic compound are added. Can be separated into two organic phases containing. Only the organic phase can be treated in the purification step and the aqueous phase can be treated separately in the aliphatic carboxylic acid recovery step.

Further, when a hydrophobic catalyst is used, the catalyst is distributed to the organic phase when water is added before filtering the catalyst. It is preferable to filter the organic phase after the addition of water, as compared with filtering the reaction solution as it is, since the amount of the solution to be filtered becomes smaller.

(3) Catalyst The catalyst is not particularly limited, and any known catalyst (compound) can be used as long as it is used as a catalyst for oxidative esterification. Further, both so-called homogeneous catalysts and heterogeneous catalysts can be used.

Specifically, the palladium-bismuth compound and the palladium-lead compound disclosed in JP-A-63-174950 or JP-A-62-273927; the palladium disclosed in JP-A-8-231466. -Gold compound; the palladium-IB group (Group 11) -based composition disclosed in JP 2001-162163 A can be used as a catalyst.

In addition, in the method for producing an aromatic-substituted alkyl ester of the present invention, in order to further improve the catalytic activity, in addition to the catalyst comprising the metal-containing composition in which the Pd and Group 11 elements are supported on the carrier, In order to prevent the elution of Pd and Group 11 elements of the periodic table into the reaction solution during the reaction, if necessary, Group 1, Group 2, Group 3, Group 4 and Group 8 of the Periodic Table 8
Tribes, 9 tribes, 10 tribes, 11 tribes, 12 tribes, 14 tribes,
A compound containing at least one kind of element belonging to either group 15 or group 16 (hereinafter referred to as the second element group) may be further used as a catalyst addition component. As the compound containing these second element groups, bismuth compounds, alkali metal compounds, alkaline earth metal compounds and the like are more preferable, bismuth acetate, bismuth acetate oxide, bismuth nitrate, potassium acetate, sodium acetate, cesium acetate, potassium nitrate, Particularly preferred are barium acetate, barium nitrate and the like. The compound containing the second element group may be a hydrate.

As described above, in the method for producing an aromatic-substituted alkyl ester of the present invention, Pd and 1 are used as the catalyst.
In addition to the metal-containing composition in which the Group 1 element is supported on a carrier,
A compound containing the above-mentioned second element group may be further used, if necessary. The compound containing the second element group may be added to the reaction solution in the form of a compound, or may be further supported on a carrier carrying Pd and a Group 11 element.

When the second element group is added to the reaction liquid in the form of a compound, it is preferable to add it so that the metal ion concentration is 0.5% by mass or less.

When the catalyst used in the present invention is a supported heterogeneous catalyst such as the above composition, when the supported component is eluted, there is a possibility that the catalytic activity may be lowered and the eluted component may be precipitated. Therefore, it is desirable to suppress elution of the catalyst component as much as possible. In an oxidizing atmosphere, elution of metal components may occur easily, and in that case, it is desirable to control the oxygen partial pressure in the system. The oxygen partial pressure can be appropriately set depending on the catalyst component, the amount of the catalyst supported, and the like. For example, P
When carrying d, the oxygen partial pressure in the system should be 0.785M.
The elution of Pd can be suppressed or prevented by controlling to Pa or less.

In the present invention, the catalyst can also be reused. In this case, the catalyst can be recycled by performing solid-liquid separation by filtration or the like.

When the aromatic carboxylic acid is precipitated in the reaction solution, it is preferable to carry out the step of removing the aromatic carboxylic acid from the catalyst. The by-produced aromatic carboxylic acid has a low solubility in the reaction solution. For example, terephthalic acid is almost insoluble in the reaction solution, and may be precipitated in the reactor. The precipitated terephthalic acid may be accumulated in the system if it is filtered together with the catalyst and recycled as it is. Therefore, when there is precipitation of aromatic carboxylic acid, it is preferable to include a step of removing the aromatic carboxylic acid from the catalyst. The removal method can be carried out, for example, by washing with an aqueous alkaline solution and extracting into the aqueous phase.

(4) Production of Aromatic Substituted Alkyl Ester In the method for producing an aromatic substituted alkyl ester of the present invention,
An aromatic substituted alkyl ester is produced by reacting a raw material containing each of the above components with an alkyl substituted aromatic compound, an aliphatic carboxylic acid and oxygen in the presence of the catalyst.

The reaction ratio of the alkyl-substituted aromatic compound and the aliphatic carboxylic acid may be such that the molar ratio of the aliphatic carboxylic acid to the alkyl group of the alkyl-substituted aromatic compound is larger than the stoichiometric ratio, and usually, the same. The molar ratio is within a range of double to 20 times, and preferably within the range of equimolar to 10 times. Within such a range, the aromatic substituted alkyl ester can be produced more efficiently.

An aromatic substituted alkyl ester can be obtained by subjecting the above-mentioned alkyl-substituted aromatic compound and an aliphatic carboxylic acid to an oxidative esterification reaction in the presence of the catalyst. The oxidation reaction is oxygen (molecular oxygen)
In the liquid or vapor phase in the presence of That is, in the present invention, the oxidation reaction can be performed in the liquid phase or the gas phase. The oxygen gas may be diluted with an inert gas such as nitrogen gas, helium gas, argon gas or carbon dioxide gas. Air can also be used as the oxygen gas. The method of supplying oxygen gas to the reaction system is not particularly limited.

The form of the oxidative esterification reaction may be any of continuous type, batch type, semi-batch type, etc., and is not particularly limited. When a batch type is adopted as the reaction form of the catalyst, the catalyst may be charged together with the raw materials in the reactor. When a continuous system is adopted as the reaction mode, it may be filled in the reaction apparatus in advance or continuously charged in the reaction apparatus together with the raw materials. Therefore, the catalyst may be used in any form of a fixed bed, a fluidized bed and a suspension bed.

The amount of the catalyst used may be set according to the kind or combination of the alkyl-substituted aromatic compound and the aliphatic carboxylic acid, the composition of the catalyst, the reaction conditions and the like, and is not particularly limited, but fixed, for example. In the case of a bed, the feed rate of the raw material liquid per unit time per unit catalyst volume is preferably about 0.01 to 100 h ⁻¹ ,
Further, in the case of a suspension bed, the amount of palladium metal is preferably about 0.01 to 30 parts by weight with respect to 100 parts by weight of the alkyl-substituted aromatic compound which is the reaction substrate.

The reaction conditions such as reaction temperature, reaction pressure and reaction time may be set according to the kind and combination of the alkyl-substituted aromatic compound and the aliphatic carboxylic acid, the composition of the catalyst and the like, and are not particularly limited. No, but reaction temperature is usually 8
The range of 0 ° C to 200 ° C is preferable. Reaction temperature is 80
If the temperature is lower than 0 ° C, the reaction rate may be too slow, and the aromatic substituted alkyl ester may not be efficiently produced. On the other hand, when the reaction temperature is higher than 200 ° C., side reactions including combustion are likely to occur, so that the aromatic-substituted alkyl ester may not be efficiently produced. In addition, the aliphatic carboxylic acid may cause corrosion of the reactor.

The reaction pressure may be reduced pressure, normal pressure (atmospheric pressure) or increased pressure. When oxygen gas (non-diluted oxygen gas) is used in the oxidative esterification reaction, it is preferable that the pressure is in the range of normal pressure to 4.9 × 10 ⁶ Pa (gauge pressure), and air is used in the oxidation reaction. When used, the pressure is preferably in the range of normal pressure to 9.8 × 10 ⁶ Pa (gauge pressure). A reaction pressure exceeding 9.8 × 10 ⁶ Pa is not preferable from an industrial viewpoint such as reaction equipment.

The oxidative esterification reaction is carried out under the above reaction conditions when the alkyl-substituted aromatic compound and / or the aliphatic carboxylic acid used as a raw material are in a liquid state.
Although it is not particularly necessary to use a solvent, when the two cannot be mixed uniformly or the reaction is violent, the reaction can be diluted with an inert solvent such as cyclohexane.

When the aromatic substituted alkyl ester is produced by the above-mentioned oxidative esterification reaction, the production of an aromatic carboxylic acid which is a side reaction product is suppressed, and the aromatic substituted alkyl ester can be produced with good selectivity. Obtainable.

The aromatic substituted alkyl ester produced is
Further, it can be purified by known methods such as distillation, extraction and crystallization. As a result, high-purity aromatic substituted alkyl ester can be recovered.

In particular, when purifying by distillation (distillation column), it is desirable to recycle the bottom liquid of the distillation column to the reaction liquid. When distilling a high-purity aromatic-substituted alkyl ester from the column top, a part of aromatic-substituted alkyl ester may remain at the column bottom. At the bottom of the column, since aromatic carboxylic acid is present in addition to the aromatic substituted alkyl ester, when the bottom liquid is recycled to the distillation column, the aromatic carboxylic acid may accumulate. Therefore,
By recycling this bottom liquid to the reaction liquid, it is possible to avoid the accumulation of aromatic carboxylic acid. Specifically, the bottom liquid may be charged into the reactor together with the raw material before the reaction, or may be mixed with the reaction liquid after the reaction.

When the column bottom liquid and the reaction liquid are mixed, the aromatic-substituted alkyl ester in the column bottom liquid dissolves in the reaction liquid, and therefore can be sent to the purification step together with the reaction liquid. On the other hand, the aromatic carboxylic acid in the bottom liquid has low solubility in the reaction liquid and is precipitated when the bottom liquid is mixed with the reaction liquid.
The precipitated aromatic carboxylic acid is filtered together with the catalyst,
It can be removed from the catalyst if desired.

By adopting such a recycling system, it is possible to obtain the total amount of the aromatic-substituted alkyl ester produced, and at the same time solve the problem of the accumulation of aromatic carboxylic acid.

Among the aromatic substituted alkyl esters obtained by the production method of the present invention, for example, p-methylbenzyl acetate and p-xylylene diacetate are various chemicals such as raw materials for synthetic resins such as polyester resins, perfumes and solvents. It is a compound suitable as a drug and a raw material of these chemicals.

[0065]

EFFECTS OF THE INVENTION By controlling the amount of water in the reaction solution, it is possible to suppress the hydrolysis of the aromatic-substituted alkyl ester and also to suppress the decrease in the production amount of the aromatic-substituted alkyl ester due to two-phase separation of the reaction solution. Can be planned.

As described above, in the present invention, by controlling the amount of water in the raw material, or by controlling the amount of water in the reaction solution, the hydrolysis of the aromatic-substituted alkyl ester is suppressed and the amount of water in the reaction solution is reduced. As a result of suppressing the phase separation, it is possible to suppress the production of by-products and to more efficiently produce the aromatic substituted alkyl ester.

[0067]

EXAMPLES Examples and comparative examples will be shown below to further clarify the characteristics of the present invention. However, the scope of the present invention is not limited to the scope of the embodiments.

Reference Example 1 (Preparation of catalyst) 84 g of tetrachloroauric (III) acid tetrahydrate
Was dissolved in 20 L of water and heated to 60 ° C. to prepare an aqueous gold solution. The pH of this aqueous solution was adjusted to 8.5 with an aqueous sodium hydroxide solution, and then 24.8 g of tetraammine palladium dichloride was added and dissolved.
Then, 30 g of sodium laurate was added to and dissolved in this aqueous solution to obtain a gold / palladium aqueous solution. Separately, 500 g of titanium oxide (manufactured by Saint-Gobain-Norpro) powder was added to 10 L of water, heated to 60 ° C., and while maintaining the temperature, pH was adjusted to 8.0 with 1N sodium hydroxide aqueous solution. A suspension was prepared. The above gold / palladium aqueous solution was added to the obtained suspension, and the mixture was stirred at 60 ° C. for 1 hour to immobilize the palladium precipitate and the gold precipitate on the titanium oxide surface to obtain a palladium-gold immobilizate. Then, after filtering the fixed product, washed with water,
It was dried at 120 ° C. for 6 hours. Then, the above immobilized product was calcined in air at 400 ° C. for 3 hours to obtain a supported product (palladium-gold supported on titanium oxide) in which palladium and gold were supported on titanium oxide. The supported amounts of palladium and gold in this supported material were 1.81% by mass and 6.44% by mass, respectively.

(Oxidative esterification reaction) In a 30 L rotary stirring autoclave equipped with a reflux condenser and a gas supply pipe into the reaction solution, 4.1 kg of p-xylene as an alkyl-substituted aromatic compound and an aliphatic carboxylic acid were used. Acetic acid 9.2k
g, palladium-gold 20 supported on titanium oxide as a catalyst
1 g and 4.1 g of bismuth acetate oxide were added and sealed.
Then, the system was replaced with nitrogen and pressurized with nitrogen to 1.96 MPa, and then heated to 140 ° C. while stirring at 700 rpm. After reaching the predetermined temperature, the nitrogen pressure was adjusted so that the internal pressure became 2.45 MPa. Then, air was supplied through the gas supply pipe at 0.8 N / hour while maintaining the internal pressure of 2.45 MPa.
It was supplied while circulating in the liquid at a rate of m ³ , and reacted for 3 hours.

After the reaction, the reaction solution was analyzed by gas chromatography and liquid chromatography. As a result, 7.57 kg of acetic acid, 0.95 kg of p-xylene, and p-methylbenzyl acetate (aromatic substituted alkyl ester) 2 were found in the reaction solution. .61 kg, p-xylylene diacetate (aromatic substituted alkyl ester) 1.18 kg, p-tolualdehyde (aromatic aldehyde) 0.15 kg, p-acetoxymethylbenzaldehyde (aromatic aldehyde) 0.
24 kg, p-methylbenzyl alcohol (aromatic substituted alkyl alcohol) 0.06 kg, p-acetoxymethylbenzyl alcohol (aromatic substituted alkyl alcohol) 0.07 kg, p-toluic acid (aromatic carboxylic acid) 0.21 kg, p -0.29 kg of acetoxymethylbenzoic acid (aromatic carboxylic acid) and 0.72 kg of water were included.

Example 1 The reaction solution obtained in Reference Example 1 was filtered to remove the catalyst, and 2345 g of the filtrate was placed in a 3 L flask equipped with a 15-stage glass Oldershaw distillation column to carry out distillation. Distillation was carried out at a pressure of 267 hPa and a reflux ratio of 2, and the column top temperature was 78.
Fractions from 5 ° C to 79.3 ° C were obtained. The obtained fraction is 1049g, in which acetic acid 1021g and water 28g
Was included.

From this fraction, 187.3 g was taken, and 101.8 g of p-xylene and 45.9 g of acetic acid were further added to prepare a raw material for oxidative esterification. P in this raw material
-Xylene 101.8 g, acetic acid 228.2 g, water 5.0
g was included. The concentration of water in the mixture of p-xylene, acetic acid and water was 1.5% by mass.

Into a 1 L rotary stirring type autoclave equipped with a reflux condenser and a gas supply pipe into the reaction solution, the above raw materials, 5.0 g of the above-described titanium oxide-supported palladium-gold as a catalyst and 0.1 g of bismuth acetate oxide were added. , Sealed. Then, the system was replaced with nitrogen and pressurized with nitrogen to 1.96 MPa, and then heated to 140 ° C. while stirring at 700 rpm.
After reaching the predetermined temperature, the nitrogen pressure was adjusted so that the internal pressure became 2.94 MPa. Next, air was supplied through the gas supply pipe while maintaining the internal pressure at 2.94 MPa while flowing in the liquid at a rate of 1 L / min, and reacted for 3 hours. The maximum oxygen concentration in the gas released from the autoclave is 4.
It was 0% by volume.

After the reaction, the reaction solution was analyzed by gas chromatography and liquid chromatography. As a result, the reaction liquid contained the components shown in Table 1. The conversion rate of p-xylene is 53.2%, the yield of p-methylbenzyl acetate based on the raw material p-xylene is 27.7%,
The yield of p-xylylene diacetate was 10.4%.

Comparative Example 1 1010 g of the filtrate obtained by filtering the reaction solution obtained in Reference Example 1 to remove the catalyst was placed in a 2 L flask equipped with a V-shaped tube and subjected to simple distillation. At a pressure of 267 hPa, a gas phase temperature of 7
The fraction up to 5.9 ° C was obtained. The obtained fraction is 589
g, which contained 474 g of acetic acid, 65 g of p-xylene, and 49 g of water.

From this fraction, 211.1 g was taken, and p-xylene (78.5 g) and acetic acid (58.0 g) were further added to prepare a raw material for oxidative esterification. P in this raw material
-Xylene 101.8 g, acetic acid 228.2 g and water 1
7.6g was included. The concentration of water in this raw material is 5.
It was 1% by mass. This raw material is the same as the raw material of Example 1 except that the amount of water is different.

An oxidative esterification reaction was carried out in the same manner as in Example 1 except that this raw material was used to determine the composition, conversion rate and yield of the reaction solution. The results are shown in Table 1.

Comparing with Example 1, p-
The yields of methylbenzyl acetate and p-xylylene diacetate decreased, and other aromatic compounds as by-products increased.

Comparative Example 2 217.1 g was taken from the fraction of Comparative Example 1 and p-
An additional 129.6 g of xylene was used as a raw material for oxidative esterification. This raw material contains p-xylene 153.6.
g, acetic acid 175.0 g and water 18.1 g. The concentration of water in this raw material was 5.2% by mass.

An oxidative esterification reaction was carried out in the same manner as in Example 1 except that this raw material was used. During the reaction, the oxygen concentration in the gas released from the autoclave increased rapidly, and the supplied oxygen was no longer consumed. After the reaction, when the reaction liquid was extracted, the reaction liquid was separated into two phases, an aqueous phase and an organic phase. Each phase was analyzed by gas chromatography and liquid chromatography to determine the composition, conversion rate and yield of the entire reaction solution. The results are shown in Table 1.

As compared with Example 1, it was confirmed that the reaction efficiency was lowered because of separation into two phases during the reaction.

Example 2 500 m equipped with a gas supply pipe into the reaction liquid and a line for cooling the liquid distilled along with the gas and returning it into the reactor
L-rotation stirring type autoclave, p-xylene 30.8
g, 68.3 g of acetic acid, 118.4 g of cyclohexane, 5.0 g of water, 1.5 g of the above-described palladium-gold supporting titanium oxide as a catalyst and 0.03 g of bismuth acetate oxide,
Sealed. The concentration of water in the raw material excluding cyclohexane was 4.8% by mass. Then, the system was replaced with nitrogen and pressurized with nitrogen to 1.96 MPa, and then heated to 140 ° C. while stirring at 700 rpm. After reaching the predetermined temperature, the nitrogen pressure was adjusted so that the internal pressure became 2.94 MPa. Next, air was supplied through the gas supply pipe while maintaining the internal pressure at 2.94 MPa while circulating in the liquid at a rate of 4.8 L / min, and the reaction was carried out for 3 hours. The liquid distilled along with the gas separated into two phases after cooling, so only the organic phase (upper layer) was returned to the reactor.

After the reaction, the reaction solution was analyzed by gas chromatography and liquid chromatography. As a result, the reaction liquid contained the components shown in Table 1. 9.1 g of water contained in the water phase (lower layer) of the liquid that was entrained in the gas and distilled
Met. The conversion rate of p-xylene was 55.8%, the yield of p-methylbenzyl acetate based on p-xylene as a raw material was 30.1%, and the yield of p-xylylene diacetate was 15.3%. It was The concentration of water in the reaction liquid excluding cyclohexane, which is an inactive component, was 1.8% by mass.

[0084]

[Table 1]

As is clear from the above results, by setting the amount of water in the raw material or the amount of water in the reaction solution to 0.01 to 5% by mass, p- which is an alkyl-substituted aromatic compound can be obtained.
The conversion rate of xylene was improved, and the yields of p-methylbenzyl acetate and p-xylylene diacetate, which are aromatic substituted alkyl esters, were improved.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuichi Sato             5-8 Nishiomitabicho, Suita City, Osaka Prefecture             Within Nippon Shokubai F-term (reference) 4H006 AA02 AC41 AC48 BA05 BA13                       BA25 BA30 BA45 BA55 BD33                       BD52 BE30 BJ50 KA06                 4H039 CA60 CA66 CC30 CL25

Claims (3)

[Claims] 1. A mixture containing an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and water is used as a raw material, and an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen are reacted in the presence of a catalyst to thereby aromatic-substitute. A method for producing an alkyl ester, wherein the amount of water is 0.0 relative to the total amount of the alkyl-substituted aromatic compound, the aliphatic carboxylic acid and water as the raw material.
A method for producing an aromatic substituted alkyl ester, which comprises using a mixture of 1 to 5 mass%. 2. Further, at least an unreacted raw material and / or an intermediate reaction product among components present in a reaction solution obtained by reacting an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen is used as a raw material. The production method according to claim 1, comprising a step of reusing in the reaction. 3. An aromatic substitution by reacting an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and oxygen in the presence of a catalyst using a mixture containing an alkyl-substituted aromatic compound, an aliphatic carboxylic acid and water as a raw material. A method for producing an alkyl ester, which comprises reacting while extracting a part or all of water present in a reaction solution to the outside of the reaction system.