Method for producing aldehyde group-containing aromatic carboxylic acid

Abstract

The present invention addresses the problem of providing a high-purity aldehyde group-containing aromatic carboxylic acid by an industrially practicable method while using a composition that contains an aldehyde group-containing aromatic carboxylic acid ester as a starting material.　The present invention provides a method for producing an aldehyde group-containing aromatic carboxylic acid from a composition that contains an aldehyde group-containing aromatic carboxylic acid ester, the method including: a suspension step in which the composition is mixed with water and stirred so as to obtain an aqueous suspension; an addition reaction step in which a sulfite is added to the aqueous suspension and subjected to an addition reaction with the aldehyde group-containing aromatic carboxylic acid ester in the aqueous suspension so as to obtain an addition reaction product of an aldehyde group-containing aromatic carboxylic acid; a solid-liquid separation step in which insoluble matter is removed from the aqueous suspension after the addition reaction step so as to obtain an aqueous solution; a cleaning step in which an aromatic hydrocarbon or an ether is added to the aqueous solution after the solid-liquid separation step and stirred so as to obtain an aqueous solution after cleaning by separating an aqueous layer after standing; a desorption reaction step in which an aromatic hydrocarbon or an ether and an alkali are added to the aqueous solution after cleaning and stirred so as to cause a desorption reaction of the addition reaction product, thereby returning the addition reaction product to an aldehyde group-containing aromatic carboxylic acid ester; a liquid separation step in which the reaction solution is left to stand after the desorption reaction step so as to separate an oil layer, thereby obtaining a solution that contains the aldehyde group-containing aromatic carboxylic acid ester; and a hydrolysis step in which an acid is added to the solution that contains the

Description

Method for producing aldehyde group-containing aromatic carboxylic acid

[0001] The present invention relates to a method for producing an aldehyde group-containing aromatic carboxylic acid.

[0002] 4-Formylbenzoic acid, which is a representative example of an aldehyde group-containing aromatic carboxylic acid, is an aromatic compound having a carboxyl group and a formyl group, and is a compound useful as a raw material for various pharmaceuticals, liquid crystals, and polymer materials, etc. due to its structure.

[0003] As a method for producing 4-formylbenzoic acid, there are a method of recovering formylbenzoic acid from the oxidation product of paraxylene, a method of chlorinating the side-chain methyl group of paraxylene, decomposing the obtained chloride with nitric acid, and further recrystallizing with water to isolate 4-formylbenzoic acid, or a method of producing 4-formylbenzoic acid by dichalogenating the side chain of paratoluic acid and then performing steam distillation of an organic solvent while hydrolyzing the dichalogenide. However, these production methods have problems in terms of product quality, environmental load, and cost.

[0004] On the other hand, there is a method of producing 4-formylbenzoic acid by isolating and purifying methyl 4-formylbenzoate contained in the by-products generated when producing dimethyl terephthalate by distillation and then hydrolyzing it (Patent Document 1). If 4-formylbenzoic acid can be produced from the by-products generated when producing dimethyl terephthalate by an industrially feasible method, the waste liquid generated during the production of dimethyl terephthalate can be effectively utilized, and the raw material cost of methyl 4-formylbenzoate can also be suppressed.

[0005] However, in this method, the purity of the distilled and purified methyl 4-formylbenzoate is as low as 96%, and therefore, the purity of the produced 4-formylbenzoic acid is also as low as 98%.

[0006] One method for isolating methyl 4-formylbenzoate from a by-product generated during the production of dimethyl terephthalate involves suspending the by-product in water, adding sodium bisulfite to form a methyl 4-formylbenzoate adduct, then performing solid-liquid separation, and finally obtaining a methyl 4-formylbenzoate solution by adding an aromatic hydrocarbon or ether as an organic solvent to the resulting filtrate, i.e., an aqueous solution of the methyl 4-formylbenzoate adduct, followed by the addition of sodium hydroxide to decompose the adduct and separate and remove the aqueous layer (Patent Document 2).

[0007] However, this method leaves dimethyl terephthalate in the resulting methyl 4-formylbenzoate solution. When hydrolysis is performed using this solution, terephthalic acid, which is very difficult to purify and remove, is produced as a by-product, making it difficult to obtain high-purity 4-formylbenzoic acid.

[0008] Thus, there was a need for an industrial manufacturing method that could produce high-quality 4-formylbenzoic acid at a low cost and with a low environmental impact.

[0009] JP-A-5-201920 JP-A-50-71640

[0010] The present invention aims to provide a method for industrially implementing high-purity aldehyde-containing aromatic carboxylic acids using a composition containing an aldehyde-containing aromatic carboxylic acid ester as a starting material.

[0011] The present invention and its preferred embodiments have the following configurations: [1] A method for producing an aldehyde group-containing aromatic carboxylic acid from a composition containing an aldehyde group-containing aromatic carboxylic acid ester, comprising: a suspension step of mixing and stirring the composition with water to obtain an aqueous suspension; an addition reaction step of adding a sulfite to the aqueous suspension to cause an addition reaction with the aldehyde group-containing aromatic carboxylic acid ester in the aqueous suspension to obtain an addition product of the aldehyde group-containing aromatic carboxylic acid; a solid-liquid separation step of removing insoluble matter from the aqueous suspension after the addition reaction step to obtain an aqueous solution; a washing step of adding an aromatic hydrocarbon or ether to the aqueous solution after the solid-liquid separation step, stirring, and then separating the aqueous layer to obtain an aqueous solution after washing; an elimination reaction step of adding an aromatic hydrocarbon or ether and an alkali to the aqueous solution after washing and stirring to cause an elimination reaction of the addition product back to an aldehyde group-containing aromatic carboxylic acid ester; a liquid-liquid separation step of letting the reaction solution stand after the elimination reaction step to separate the oil layer and obtain a solution containing the aldehyde group-containing aromatic carboxylic acid ester. A method for producing an aldehyde-containing aromatic carboxylic acid, comprising a hydrolysis step of adding an acid to an aqueous dispersion of the aldehyde-containing aromatic carboxylic acid obtained by replacing the solvent in the solution containing the aldehyde-containing aromatic carboxylic acid ester after the liquid-liquid separation step with water.

[0012] [2] The method for producing an aldehyde group-containing aromatic carboxylic acid according to [1], further comprising a topping step before the hydrolysis step, in which the solvent of the solution containing the aldehyde group-containing aromatic carboxylic acid ester after the liquid-liquid separation step is replaced with water to obtain an aqueous dispersion of the aldehyde group-containing aromatic carboxylic acid ester.

[0013] [3] The method for producing an aldehyde group-containing aromatic carboxylic acid according to [1] or [2], wherein the aldehyde group-containing aromatic carboxylic acid ester is methyl 4-formylbenzoate and the aldehyde group-containing aromatic carboxylic acid is 4-formylbenzoic acid.

[0014] [4] The method for producing an aldehyde group-containing aromatic carboxylic acid according to [3], wherein the composition is a by-product of the process for producing dimethyl terephthalate.

[0015] [5] A method for producing an aldehyde group-containing aromatic carboxylic acid according to any one of [1] to [4], wherein the purity of the aldehyde group-containing aromatic carboxylic acid produced is 99% or higher.

[0016] According to the present invention, aldehyde-containing aromatic carboxylic acids can be produced in high purity from a composition containing an aldehyde-containing aromatic carboxylic acid ester.

[0017] The details of the present invention are described below.

[0018] [Raw Materials] In the method for producing an aldehyde group-containing aromatic carboxylic acid of the present invention, the aldehyde group-containing aromatic carboxylic acid is produced from a composition containing an aldehyde group-containing aromatic carboxylic acid ester. A preferred example of the composition containing the aldehyde group-containing aromatic carboxylic acid ester is a composition containing methyl 4-formylbenzoate, which is a by-product of the process for producing dimethyl terephthalate.

[0019] [Suspension step] The above manufacturing method includes a suspension step in which the composition is mixed and stirred with water to obtain an aqueous suspension.

[0020] The amount of water in the suspension step is preferably 10 to 30 times the mass of the aldehyde group-containing aromatic carboxylic acid ester. By using 10 times or more the mass of water, the recovery rate of the aldehyde group-containing aromatic carboxylic acid ester can be more effectively increased. On the other hand, it is more economical if the amount of water is 30 times or less, more preferably 20 times or less.

[0021] [Addition reaction step] The above production method includes an addition reaction step in which a sulfite is added to the aqueous suspension and reacted with the aldehyde group-containing aromatic carboxylic acid ester in the aqueous suspension to form an addition product of the aldehyde group-containing aromatic carboxylic acid ester. By changing the aldehyde group-containing aromatic carboxylic acid ester into the addition product, water solubility can be imparted.

[0022] The sulfite is preferably a bisulfite such as sodium bisulfite or potassium bisulfite, and more preferably sodium bisulfite.

[0023] The amount of sulfite used in the addition reaction step is preferably 1.0 molar to 2.5 molars relative to the aldehyde group-containing aromatic carboxylic acid ester. By using an amount of 1.0 molar to 2.5 molars, more preferably 1.5 molars, the conversion rate to the adduct can be effectively improved. On the other hand, by using an amount of 2.5 molars or less, more preferably 2.0 molars, the conversion rate to the adduct is more efficient in terms of improving the conversion rate relative to the amount of sulfite used, making it economical.

[0024] The reaction temperature in the addition reaction step is preferably 20°C to 80°C, and more preferably 40°C to 60°C.

[0025] [Solid-Liquid Separation Step] The manufacturing method includes a solid-liquid separation step to obtain an aqueous solution by removing insoluble matter from the aqueous suspension after the addition reaction step. Since the addition reaction product generated in the addition reaction step is water-soluble, it dissolves in an aqueous solvent and can be selectively separated from water-insoluble impurities.

[0026] [Washing Step] The manufacturing method includes a washing step in which an aromatic hydrocarbon or ether is added to the aqueous solution after the solid-liquid separation step and stirred, and after standing, the aqueous layer is separated to obtain an aqueous solution after washing. By adding the aromatic hydrocarbon or ether to the aqueous solution and stirring, organic solvent-soluble impurities that could not be separated in the solid-liquid separation step are dissolved in the aromatic hydrocarbon or ether and selectively separated from the aqueous solution.

[0027] The separation mechanism in the aforementioned washing process is thought to utilize the difference between the hydrophilicity of the addition product and the hydrophobicity of the impurities. That is, the addition product has an α-hydroxysulfonate structure (-CH(OH)SO ３The presence of Na (sodium) results in high water solubility, allowing the compound to be stably retained in the aqueous layer. On the other hand, lipid-soluble impurities such as dimethyl terephthalate have a high affinity for aromatic hydrocarbons or ethers, and therefore selectively migrate to these organic solvent layers. Furthermore, it is presumed that lipid-soluble impurities adsorbed on the surface of the addition reaction product particles are effectively removed at the interface between the aqueous layer and the organic solvent layer. As a result, it becomes possible to selectively remove only impurities while retaining the protected target product as an addition reaction product in the aqueous layer, which is thought to contribute to improving the purity of the aldehyde group-containing aromatic carboxylic acid ester obtained in the subsequent elimination reaction step.

[0028] In the washing step, the ether is preferably diethyl ether, diisopropyl ether, or methyl tert-butyl ether. The aromatic hydrocarbon in the washing step is preferably benzene, toluene, xylene, or mesitylene. Among these, toluene is particularly preferred due to its excellent solubility in impurities, its ability to separate from water, and its low cost.

[0029] The amount of aromatic hydrocarbon or ether used in the cleaning step is preferably 0.5 to 5.0 times the mass of the aldehyde group-containing aromatic carboxylic acid ester in total. By using an amount of 0.5 times or more, more preferably 1.0 time or more, the cleaning efficiency can be increased. On the other hand, it is more economical if the amount used is 5.0 times or less, more preferably 3.0 times or less.

[0030] The washing temperature in the washing step is preferably 20°C to 80°C. If the washing temperature is 20°C or higher, more preferably 40°C or higher, the adducts will dissolve effectively and crystal precipitation can be suppressed. If the washing temperature is 80°C or lower, more preferably 60°C or lower, the adducts will not decompose and the yield will be high.

[0031] [Desorption reaction step] The above manufacturing method includes an elimination reaction step in which the addition product is desorbed by adding an aromatic hydrocarbon or ether and an alkali to the aqueous solution after washing and stirring, thereby returning it to an aldehyde group-containing aromatic carboxylic acid ester.

[0032] As the alkali, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are preferred, and sodium hydroxide is more preferred.

[0033] The mechanism of action of the alkali in the aforementioned elimination reaction step is thought to be to promote the elimination of sulfite ions from the α-hydroxysulfonate structure of the addition product. Under basic conditions due to alkali, it is presumed that sulfite ions are eliminated by the E1cb mechanism, and the original aldehyde group is regenerated. Alkali metal hydroxides such as sodium hydroxide and potassium hydroxide all generate hydroxide ions in aqueous solutions, and can efficiently carry out this elimination reaction.

[0034] The amount of alkali used in the elimination reaction step is preferably 1.0 molar to 2.5 molar times the amount of the aldehyde group-containing aromatic carboxylic acid ester. If the amount of alkali used is 1.0 molar time or more, more preferably 1.5 molar times or more, the decomposition of the adduct can be effectively completed. On the other hand, if the amount of sodium hydroxide used is 2.5 molar times or less, more preferably 2.0 molar times or less, hydrolysis, which is a side reaction, can be suppressed, and the decrease in recovery rate can be suppressed.

[0035] In the elimination reaction step, the ether is preferably diethyl ether, diisopropyl ether, or methyl tert-butyl ether. The aromatic hydrocarbon in the elimination reaction step is preferably benzene, toluene, xylene, or mesitylene. Among these, toluene is particularly preferred due to its excellent solubility in methyl 4-formylbenzoate, its excellent separation from water, and its low cost.

[0036] The temperature in the elimination reaction step is preferably 0 to 50°C, and more preferably 5 to 25°C.

[0037] [Liquid Separation Step] The manufacturing method includes a liquid separation step in which the oil layer is separated by allowing it to stand after the elimination reaction step to obtain a solution containing the aldehyde group-containing aromatic carboxylic acid ester. The aldehyde group-containing aromatic carboxylic acid ester obtained in the elimination reaction step dissolves into the oil layer, and the oil layer becomes a solution containing the aldehyde group-containing aromatic carboxylic acid ester. The aqueous layer incorporates excess alkali supplied in the elimination reaction step and nitrite produced by the elimination reaction of the addition reaction product. By separating and removing the aqueous layer from the oil layer, the purity of the aldehyde group-containing aromatic carboxylic acid ester in the solution can be improved.

[0038] [Water Washing Step] The manufacturing method preferably includes a water washing step after the liquid-liquid separation step, in which water is added to the solution containing the aldehyde group-containing aromatic carboxylic acid ester, stirred, and then separated and removed after standing. This water washing step removes alkalis and sulfites that could not be removed in the liquid-liquid separation step, thereby further improving the purity of the aldehyde group-containing aromatic carboxylic acid ester in the solution.

[0039] The aforementioned washing process may be repeated multiple times.

[0040] [Topping Step] The manufacturing method preferably includes a topping step before the hydrolysis step, in which the solvent of the solution containing the aldehyde group-containing aromatic carboxylic acid ester after the liquid-liquid separation step is replaced with water to obtain an aqueous dispersion of the aldehyde group-containing aromatic carboxylic acid ester. Replacing the solvent of the solution containing the aldehyde group-containing aromatic carboxylic acid ester with water improves the contact efficiency between the aldehyde group-containing aromatic carboxylic acid ester and the acid in the hydrolysis step, allowing the hydrolysis reaction in the hydrolysis step to proceed more rapidly.

[0041] As a method for replacing the solvent with water, it is preferable to remove the solvent by distillation. The conditions for removing the solvent by distillation are preferably 10°C to 100°C under reduced pressure, and more preferably 30°C to 70°C. Under normal pressure, it is preferable to have a temperature above the boiling point of the organic solvent and below 100°C.

[0042] [Hydrolysis Step] The manufacturing method includes a hydrolysis step of adding an acid to an aqueous dispersion of an aldehyde group-containing aromatic carboxylic acid ester obtained by substituting the solvent of the solution containing the aldehyde group-containing aromatic carboxylic acid ester after the liquid separation step or the solution containing the aldehyde group-containing aromatic carboxylic acid ester after the topping step with water, and performing hydrolysis.

[0043] As the acid, mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid are preferable, and hydrochloric acid is more preferable.

[0044] It is presumed that the role of the acid in the hydrolysis step is to activate the carbonyl carbon of the ester bond and promote the nucleophilic attack by water molecules. Mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid act as proton donors and are considered to enhance the electrophilicity of the carbonyl carbon by protonating the carbonyl oxygen. As a result, the nucleophilic attack by water molecules is promoted, and it is considered that the hydrolysis reaction proceeds via a tetrahedral intermediate.

[0045] The amount of hydrochloric acid used in the hydrolysis step is preferably 1 to 10 times the mass of methyl 4-formylbenzoate. If the amount of hydrochloric acid used is 1 or more times the mass, the progress of the reaction can be accelerated. On the other hand, if it is 10 or less times the mass, a decrease in productivity can be suppressed.

[0046] The reaction temperature in the hydrolysis is preferably 50°C or higher and 120°C or lower, more preferably 80°C or higher and 100°C or lower.

[0047] [Second Solid-Liquid Separation Step] The manufacturing method preferably includes a second solid-liquid separation step of subjecting the reaction solution after the hydrolysis step to solid-liquid separation to obtain an aldehyde group-containing aromatic carboxylic acid. By performing solid-liquid separation, a solid aldehyde group-containing aromatic carboxylic acid with excellent handleability can be taken out.

[0048] Hereinafter, the present invention will be described in more detail with reference to examples.

[0049] [Example 1] (Suspension Step) 20.5 g of a composition containing 33.1% by mass (6.8 g, 0.041 mol) of methyl 4-formylbenzoate, a by-product of the process for producing dimethyl terephthalate, and 96.9 g of water were placed in a 300 ml four-necked flask equipped with a thermometer. The atmosphere in the system was replaced with nitrogen, and the mixture was melted at 90°C while stirring. Thereafter, the mixture was cooled to 50°C while continuing nitrogen replacement and stirring to obtain an aqueous suspension.

[0050] (Addition reaction step) After the suspension step described above, 6.4 g (0.06 mol) of sodium bisulfite was dissolved in 16.9 g of water, and this aqueous solution was added dropwise to the stirred aqueous suspension. After the entire volume of the aqueous solution was added dropwise, the addition reaction was carried out at 50°C for 2 hours with stirring to obtain an aqueous suspension containing the addition product of methyl 4-formylbenzoate.

[0051] (Solid-Liquid Separation Process) The aqueous suspension after the addition reaction process described above was subjected to solid-liquid separation to obtain an aqueous solution. The mother liquor obtained by washing the solid residue with 16.9 g of water was combined with the aqueous solution to obtain the aqueous solution after the solid-liquid separation process.

[0052] (Washing process) The aqueous solution obtained after the solid-liquid separation process was placed in a 300 ml four-necked flask equipped with a thermometer, 16.9 g of toluene was added and stirred, and after standing, the aqueous layer was separated to obtain a washed aqueous solution containing the addition reaction product of 4-formylbenzoate.

[0053] (Desorption reaction step) 16.9 g of toluene was added to the aqueous solution after the above washing step, and 9.9 g (0.06 mol) of 25% sodium hydroxide aqueous solution was added dropwise while controlling the temperature to 10-20°C. After the entire amount of sodium hydroxide was added dropwise, the mixture was stirred at 15°C for 1 hour to desorb the addition product from above and return it to methyl 4-formylbenzoate.

[0054] (Liquid Separation Step) The reaction solution after the above desorption reaction step was allowed to stand to separate the oil layer, and a toluene solution containing methyl 4-formylbenzoate was obtained.

[0055] (Washing process) 8.1 g of water was added to the above toluene solution and stirred for 30 minutes. Then it was allowed to stand, and the aqueous layer was separated and removed to obtain the oil layer solution.

[0056] 8.1 g of water was added to the above solution and stirred for 30 minutes. After standing, the aqueous layer was separated and removed to obtain a toluene solution with a yield of 84% methyl 4-formylbenzoate (methyl 4-formylbenzoate content: 5.7 g, 0.035 mol).

[0057] Analysis of the obtained methyl 4-formylbenzoate by high-performance liquid chromatography (HPLC) revealed a chemical purity of 99.9 area% (excluding toluene).

[0058] (Topping process) 119.9 g of water was added to the above toluene solution (containing methyl 4-formylbenzoate: 5.3 g, 0.032 mol), and the pressure was reduced to 12.0 to 14.7 kPa. The temperature was then gradually increased to 50°C, and the toluene was removed by distillation to obtain an aqueous dispersion in which methyl 4-formylbenzoate was suspended in the aqueous solvent.

[0059] (Hydrolysis process) 27 g of hydrochloric acid was added to the aqueous dispersion of methyl 4-formylbenzoate described above, and the temperature was raised while controlling it to stay within the range of 90-100°C. After the temperature was raised, the mixture was stirred for 6 hours. After stirring, it was cooled to 20-30°C.

[0060] (Second solid-liquid separation step) After the hydrolysis step described above, the 4-formylbenzoic acid crystals were filtered and washed with 67.7 g of water.

[0061] The obtained crystals were dried under reduced pressure at 50°C for 12 hours to yield 4.7 g (0.032 mol) of 4-formylbenzoic acid in a yield of 97.9% (based on methyl 4-formylbenzoate).

[0062] Analysis of the obtained 4-formylbenzoic acid by high-performance liquid chromatography (HPLC) revealed a chemical purity of 99.8 area percent.

[0063] [Example 2] (Suspension step to water washing step) In the desorption reaction step, toluene was replaced with 16.9 g of xylene, which was added to the aqueous solution after the washing step. The suspension step to the water washing step was carried out in the same manner as in Example 1, and a xylene solution containing 4-formylbenzoate was obtained in yield of 84%.

[0064] Analysis of the obtained methyl 4-formylbenzoate by high-performance liquid chromatography (HPLC) revealed a chemical purity of 99.9 area percent (excluding xylene).

[0065] (Topping process) In Example 2, the topping process was not performed.

[0066] (Hydrolysis step to second solid-liquid separation step) Except for adding 106 g of water and 27 g of hydrochloric acid to the xylene solution obtained in the water washing step described above, the hydrolysis step to the second solid-liquid separation step was carried out in the same manner as in Example 1, and 4-formylbenzoic acid crystals were obtained in a yield of 88.0%.

[0067] Analysis of the obtained 4-formylbenzoic acid by high-performance liquid chromatography (HPLC) revealed a chemical purity of 99.7 area percent.

[0068] [Comparative Example 1] (Suspension Process to Solid-Liquid Separation Process) The suspension process to the solid-liquid separation process was carried out in the same manner as in Example 1.

[0069] (Cleaning process) In Comparative Example 1, the cleaning process was not performed.

[0070] (Desorption reaction step to water washing step) The procedure from the desorption reaction step to the water washing step was carried out in the same manner as in Example 1, except that the aqueous solution after the solid-liquid separation step was used instead of the aqueous solution after the washing step, and a toluene solution containing methyl 4-formylbenzoate was obtained in a yield of 45.3%.

[0071] Analysis of the obtained methyl 4-formylbenzoate by high-performance liquid chromatography (HPLC) revealed a chemical purity of 96.2 area% (excluding toluene).

[0072] (Topping process) 119.9 g of water was added to the above toluene solution (containing 3.0 g, 0.019 mol of 4-formylbenzoate), and the pressure was reduced to 12.0 to 14.7 kPa. The temperature was then gradually increased to 50°C, and the toluene was removed by distillation to obtain an aqueous dispersion in which 4-formylbenzoate was suspended in the aqueous solvent.

[0073] (Hydrolysis step to second solid-liquid separation step) 27 g of hydrochloric acid was added to the aqueous dispersion of methyl 4-formylbenzoate described above, and the hydrolysis step to the second solid-liquid separation step was carried out in the same manner as in Example 1, to obtain crystals of 4-formylbenzoic acid in a yield of 99.1%.

[0074] Analysis of the obtained 4-formylbenzoic acid by high-performance liquid chromatography (HPLC) revealed a chemical purity of 96.6 area%.

[0075] The test results are shown in Table 1. The following are possible reasons why the manufacturing method of the present invention exhibits excellent effects: The addition reaction step selectively extracts the aldehyde group-containing aromatic carboxylic acid ester as a water-soluble addition product into the aqueous layer, thereby efficiently removing water-insoluble impurities. The washing step removes organic solvent-soluble impurities, preventing contamination in subsequent steps. The elimination reaction step and liquid-liquid separation step selectively extract the target aldehyde group-containing aromatic carboxylic acid ester into the organic layer, separating it from water-soluble inorganic salts. Then, the hydrolysis step efficiently obtains the aldehyde group-containing aromatic carboxylic acid from the purified aldehyde group-containing aromatic carboxylic acid ester. It is presumed that the synergistic action of these steps makes it possible to produce high-purity aldehyde group-containing aromatic carboxylic acids.

[0076]

[0077] The aldehyde group-containing aromatic carboxylic acids, such as 4-formylbenzoic acid, produced by the present invention are useful as raw materials for various pharmaceuticals, liquid crystals, and polymer materials.

Claims

1. A method for producing an aldehyde-containing aromatic carboxylic acid from a composition containing an aldehyde-containing aromatic carboxylic acid ester, comprising: a suspension step of mixing and stirring the composition with water to obtain an aqueous suspension; an addition reaction step of adding a sulfite to the aqueous suspension to cause an addition reaction with the aldehyde-containing aromatic carboxylic acid ester in the aqueous suspension to obtain an addition product of the aldehyde-containing aromatic carboxylic acid ester; a solid-liquid separation step of removing insoluble matter from the aqueous suspension after the addition reaction step to obtain an aqueous solution; a washing step of adding an aromatic hydrocarbon or ether to the aqueous solution after the solid-liquid separation step, stirring, and then separating the aqueous layer after standing to obtain a washing aqueous solution; an elimination reaction step of adding an aromatic hydrocarbon or ether and an alkali to the washing aqueous solution and stirring to cause an elimination reaction of the addition product back to an aldehyde-containing aromatic carboxylic acid ester; and a liquid-liquid separation step of allowing the reaction solution to stand after the elimination reaction step to separate the oil layer and obtain a solution containing the aldehyde-containing aromatic carboxylic acid ester. A method for producing an aldehyde-containing aromatic carboxylic acid, comprising a hydrolysis step of adding an acid to an aqueous dispersion of the aldehyde-containing aromatic carboxylic acid obtained by replacing the solvent in the solution containing the aldehyde-containing aromatic carboxylic acid ester after the liquid-liquid separation step with water.

2. The method for producing an aldehyde group-containing aromatic carboxylic acid according to claim 1, further comprising a topping step before the hydrolysis step, in which the solvent of the solution containing the aldehyde group-containing aromatic carboxylic acid ester after the liquid-liquid separation step is replaced with water to obtain an aqueous dispersion of the aldehyde group-containing aromatic carboxylic acid ester.

3. The method for producing an aldehyde group-containing aromatic carboxylic acid according to claim 1 or 2, wherein the aldehyde group-containing aromatic carboxylic acid ester is methyl 4-formylbenzoate, and the aldehyde group-containing aromatic carboxylic acid is 4-formylbenzoic acid.

4. The method for producing an aldehyde group-containing aromatic carboxylic acid according to claim 3, wherein the composition is a by-product of the process for producing dimethyl terephthalate.

5. The method for producing an aldehyde group-containing aromatic carboxylic acid according to claim 1 or 2, wherein the purity of the aldehyde group-containing aromatic carboxylic acid produced is 99% or higher.

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