JP3232796B2 - Method for producing p-acetoxybenzoic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the production of p-cresol from p-cresol.
The present invention relates to a method for producing acetoxybenzoic acid.
p-acetoxybenzoic acid is regarded as industrially important as a raw material of a liquid crystalline polymer.

[0002]

2. Description of the Related Art Since p-cresol is a p-methylated form of phenol, it exhibits an oxidation-suppressing action characteristic of phenols. In an ordinary oxidation reaction with molecular oxygen, a methyl group is oxidized to a carboxyl group. It is difficult.
Therefore, a method is employed in which the phenolic hydroxyl group is protected by esterification to counteract its oxidation inhibitory action.

A method for producing p-acetoxybenzoic acid by esterifying p-cresol with acetic anhydride and oxidizing it with a molecular oxygen-containing gas is disclosed in JP-A-62-2426.
No. 44, JP-A-64-63549 and JP-A-2-225 are known.

[0004]

However, in all of these methods, the selectivity of p-acetoxybenzoic acid is not sufficient due to the formation of a large amount of by-products, and the conversion of p-acetoxybenzoic acid separated from the reaction product solution is not sufficient. The crystals are markedly colored. Further, when a reaction filtrate containing p-acetoxybenzoic acid or a catalyst is used for the next oxidation reaction, there is a problem that the yield of p-acetoxybenzoic acid is remarkably reduced, and this is not a preferable method.

[0005]

Means for Solving the Problems Accordingly, the present inventors have:
In a method for producing p-acetoxybenzoic acid by esterifying p-cresol with acetic anhydride and oxidizing it with a molecular oxygen-containing gas, a method for obtaining a desired product having a good color tone with a high selectivity in a good yield is to be developed. The purpose of this study was to study intensively and to find that a zirconium compound was present in the reaction system in addition to the variable valence metal compounds such as cobalt and manganese and bromine compounds that have been conventionally used as catalysts. The invention has been reached.

[0006] That is, the present invention provides a method for continuously acetylating p-cresol and oxidizing it with a molecular oxygen-containing gas using a catalyst comprising a cobalt compound, a manganese compound and a bromine compound in an acetic acid solvent in the presence of acetic anhydride. P
-A method for producing p-acetoxybenzoic acid, wherein a zirconium compound is present in a reaction system.

Hereinafter, the method of the present invention will be described specifically.

In the method of the present invention, p-cresol is acetylated with acetic anhydride in an acetic acid solvent and then contacted with a molecular oxygen-containing gas in the presence of a catalyst.

[0009] The amount of acetic acid used is 0.5 to 0.5% of p-cresol.
7 times by weight, preferably 1.5 to 3 times by weight is appropriate.
If the amount of acetic acid is less than 0.5 times by weight, a sufficient oxidation rate cannot be obtained, and the reaction product becomes a slurry with a high concentration and is difficult to handle. It is difficult to get stable. On the other hand, when the amount of acetic acid used is 7 times by weight or more, the economic burden due to the combustion decomposition of acetic acid increases, and the volumetric efficiency of the reactor is disadvantageously reduced.

The acetic anhydride may be used in an amount sufficient to acetylate p-cresol and further remove water produced as a by-product of oxidation. The amount of acetic anhydride used is 1.8 to 7 based on p-cresol. Molar times, preferably 2 to 3.5
It is a molar amount.

As a catalyst, a cobalt compound and a bromine compound are used as main components, and a manganese compound is used in combination with these compounds in order to enhance the catalytic activity. In this case, the cobalt compound and the manganese compound are soluble in a reaction product such as a salt of a lower aliphatic carboxylic acid such as bromide, hydroxide, carbonate, or acetic acid, a salt of naphthenic acid, or acetylacetonate, and hinder the reaction. Compounds that do not contain a suitable counterion are suitable.

The bromine compounds include bromine, hydrogen bromide, cobalt bromide, manganese bromide, ammonium bromide,
Inorganic bromine compounds such as alkali metal bromides and organic bromine compounds such as tetrabromoethane, bromoacetic acid and benzyl bromide can be used.

[0013] The amount of the cobalt compound used is such that the amount of the cobalt metal used is 0.1 to the total amount of acetic acid and acetic anhydride.
It is appropriate that the content be in the range of 0.5 to 0.5% by weight. If the amount of the cobalt catalyst used is less than 0.05% by weight, a sufficient reaction rate cannot be obtained. If the amount exceeds 0.5% by weight, the time required to separate the cobalt catalyst from the target product increases, and the color impurities are reduced. It is disadvantageous because life increases.

In the present invention, a manganese compound is used in addition to the cobalt compound. However, the manganese compound is used so that the amount of manganese metal used is in the range of 0.2 to 40% by weight based on the cobalt metal. Is desirable. When the amount of the manganese compound is less than the above range, the catalytic activity decreases, and when the amount is more than the above range, the amount of by-produced coloring impurities increases, which is not preferable.

The amount of the bromine compound used is suitably in the range of 0.6 to 5 times by weight, especially 1 to 3 times by weight, based on the amount of cobalt metal as a bromine atom.

When the amount of the bromine compound is less than 0.6 times by weight, sufficient catalytic activity cannot be obtained, and when the amount exceeds 5 times by weight, the catalytic activity tends to decrease, and the contamination of the product by bromine and the catalyst The burden of expenses becomes remarkable, which is not preferable.

In the present invention, a zirconium compound is further present in the reaction system in addition to the above-mentioned cobalt compound, bromine compound and manganese compound. The present inventors have found that the combined use of a zirconium compound enhances the catalytic activity and also reduces the amount of by-produced coloring impurities.

As the zirconium compound, zirconium compounds which are soluble in acetic acid, such as zirconium bromide, zirconyl acetate and zirconium acetate and which do not contain a counter ion which hinders the reaction, are suitable. The amount of the zirconium compound used is suitably such that the amount of the zirconium metal used corresponds to 7.5 to 30% by weight, preferably 8 to 20% by weight, based on the cobalt metal used as the catalyst component. It is. If the amount of the zirconium compound is less than this range, the effect of addition becomes weak. If the amount is more than this range, the cost burden and the labor for separation increase, but no particular effect is obtained, which is disadvantageous.

In practicing the present invention, the inside of the reactor is first replaced with nitrogen, and the reaction temperature is increased to 60 ° C. or higher, preferably
The above is maintained for about 30 to 90 minutes to complete the acetylation. If the reaction temperature is too low, the protection of the phenolic hydroxyl group by esterification becomes insufficient and the oxidation inhibiting action of the phenols is exhibited, so that the next oxidation reaction is stopped at a low conversion rate. The reaction temperature in the oxidation is 80 to 180 ° C,
Preferably, the range of 100 to 150 ° C. is appropriate. 80
At a temperature lower than 180 ° C., the reaction rate becomes extremely slow. On the other hand, at a reaction temperature higher than 180 ° C., the decomposition of the reaction product into carbon dioxide and the by-product of coloring impurities increase, which is not preferable.

As the molecular oxygen-containing gas used as the oxidizing agent, pure oxygen or industrial exhaust gas can be used, but industrially, ordinary air or a mixed gas of air and industrial exhaust gas is suitable.

As for the oxygen partial pressure of the reaction system, the total reaction pressure is in the range of 5 to 40 atm, particularly 8 to 30 atm, and the oxygen concentration of the exhaust gas from the reactor is in the range of 1 to 8% by volume. It is preferable that the operation be performed. When the reaction pressure exceeds 40 atm, no particular advantage is obtained despite the increase in equipment costs and power cost for compressing the molecular oxygen-containing gas, and conversely, the decomposition of the reactants into carbon dioxide It is disadvantageous as it tends to increase. If the oxygen concentration of the exhaust gas exceeds 8% by volume, the possibility that the gas phase of the reactor will form an explosive mixed gas increases, and the oxygen concentration of the exhaust gas becomes 8 from the viewpoint of safety measures.
It is necessary to make the capacity% or less.

The reactor used in the present invention is preferably of a type in which forced mixing is performed, rather than a simple bubble column type. That is, in order to perform good gas-liquid mixing of the molecular oxygen-containing gas and the reaction solution, promote the dissolution of the molecular oxygen in the reaction solution, and smoothly perform the contact between the reactants in the reactor, It is preferable to use a reactor provided with a gas inlet composed of a large number of pores at the lower part of the reactor and in which forced stirring by a rotary stirring blade or forced circulation by a circulation pump outside the reactor is performed.

A reflux condenser is provided at the upper part of the reactor, and the exhaust gas is discharged through the reflux condenser to condense the solvent acetic acid, acetic anhydride, unreacted p-acetoxytoluene and the like contained in the exhaust gas. And circulate through the reactor.

As the reaction system, any of a batch system, a semi-continuous system and a continuous system can be employed.

As a method for isolating the target substance, p-acetoxybenzoic acid, from the reaction product mixture obtained by the method of the present invention, the reaction product is cooled and, if necessary, further concentrated to obtain p-acetoxybenzoic acid. Is suitable, and a method of crystallizing the solution and separating the solution from the mother liquor by solid-liquid separation is appropriate. The thus isolated p-
The acetoxybenzoic acid is purified to a desired purity by washing it with a solvent and, if necessary, recrystallizing it, and then drying it to obtain a product.

On the other hand, the mother liquor from which p-acetoxybenzoic acid has been separated contains the organic components such as p-acetoxybenzoic acid, a reaction intermediate, a catalyst and an excess of acetic anhydride in the amount of solubility. Thereafter, the catalyst and acetic anhydride can be replenished and circulated through the reaction system, and used repeatedly.

By the method of the present invention described in detail above, it has become possible to produce high-quality p-acetoxybenzoic acid in high yield.

[0028]

The present invention will be specifically described below with reference to examples.

Example 1 A titanium pressure-resistant reactor equipped with a reflux condenser and a rotary blade stirrer was charged with 120 parts of p-cresol and 300 parts of acetic anhydride (p
-2.65 mol times based on cresol), 200 parts of acetic acid (1.7 times by weight based on p-cresol), 3.128 parts of cobalt acetate tetrahydrate (cobalt based on the total amount of acetic anhydride and acetic acid) 0.15% by weight as metal), 0.172 parts of manganese acetate tetrahydrate (manganese 5.0 relative to cobalt)
0.185 parts of zirconyl acetate (10% by weight of zirconium based on cobalt), sodium bromide 1.8
0 parts (1.9 weight times bromine with respect to cobalt)
The inside of the reactor was purged with nitrogen, pressurized to a 4 atm gauge, heated to 115 ° C., and continued heating for 60 minutes.

Thereafter, the pressure was increased to 14 atm gauge with a mixed gas of 5% oxygen and 95% nitrogen, and heating was continued while blowing the mixed gas. When the absorption of oxygen started 5 minutes later, the blown gas was switched to air. Air blowing was continued at a flow rate such that the oxygen concentration in the exhaust gas became 8% or less. After 3.5 hours, the oxygen concentration in the exhaust gas was increased to 8%, so that the blowing of air was stopped.

After completion of the reaction, 665 parts by weight of the reaction product was cooled to around room temperature, and 183 parts by weight of wet crude crystals (p-acetoxybenzoic acid, 68.2% yield) obtained by solid-liquid separation were added to 50 parts by weight.
After washing with 350 parts of water-containing acetic acid and drying, 125.4 parts of a white crystal of p-acetoxybenzoic acid (62.7% yield).
I got Its purity as determined by high performance liquid chromatography was 99.5%. Further, 2.00 g of the obtained crystal of p-acetoxybenzoic acid was dissolved in dimethyl sulfoxide 2
It was dissolved in 0 ml, and the light transmittance at 400 nm measured with a 10 mm cell was 95.1%.

Further, 42.1 parts by weight (yield 21.1%) of p-acetoxybenzoic acid and 0.27 parts by weight (yield 0.15%) of p-acetoxybenzaldehyde were added to 469 parts by weight of the filtrate. Although 53.6 parts by weight of acetic anhydride was contained, p-acetoxytoluene was not detected.

As a result, the reaction yield of p-acetoxybenzoic acid was 89.3%, and the consumption of acetic anhydride was 2.2 times as much as p-cresol.

Example 2 From 469 parts by weight of the reaction filtrate obtained in Example 1,
120 parts by weight of p-cresol was added to 185 parts by weight of the remaining liquid obtained by distilling off parts by weight, and 98 parts by weight of acetic acid and 277 parts by weight of acetic anhydride were further added to adjust the ratio of p-cresol, acetic acid and acetic anhydride. A reaction solution was prepared in the same manner as in Example 1. All catalysts were supplemented by 15% of the amount added in Example 1.

The above prepared solution was reacted in the same manner as in Example 1,
After cooling, solid-liquid separation, washing and drying were performed to obtain 165 parts (yield: 82.5%) of white crystals of p-acetoxybenzoic acid. The purity of the obtained p-acetoxybenzoic acid is 99.4
%, And the light transmittance at 400 nm was 93.9%.

Further, 441 parts by weight of the filtrate contained 41.1 parts by weight (yield 20.6%) of p-acetoxybenzoic acid and 0.49 parts by weight (yield 0.27%) of p-acetoxybenzaldehyde. Although 50.3 parts by weight of acetic anhydride was contained, p-acetoxytoluene was not detected.

As a result, the reaction yield of p-acetoxybenzoic acid (the yield excluding p-acetoxybenzoic acid contained in the reaction filtrate of Example 1) was 89.5%, and the consumption of acetic anhydride Was 2.2 mol times with respect to p-cresol.

Comparative Example 1 When zirconyl acetate was not added in Example 1, the reaction yield of p-acetoxybenzoic acid was reduced to 86.5%.
Also, the yield of the isolated p-acetoxybenzoic acid was 54.
The light transmittance at 400 nm was measured and found to be 87.2%.

The consumption of acetic anhydride was 2.3 times the molar amount of p-cresol.

Comparative Example 2 475 parts by weight of the reaction filtrate obtained in Comparative Example 1
P-cresol, acetic acid, acetic anhydride and all the catalysts were added to and reacted with 185 parts by weight of the remaining liquid distilled off in the same manner as in Example 2. Since the oxygen absorption stopped, the reaction solution was cooled.

When 696 parts of the obtained reaction product solution was analyzed by high performance liquid chromatography, 26.0 parts (yield 15.6%) of p-acetoxytoluene, 119.3 parts of p-acetoxybenzoic acid, p-acetoxy Benzaldehyde 1
2.0 parts (yield 6.6%).

As a result, the yield of p-acetoxybenzoic acid (yield excluding p-acetoxybenzoic acid contained in the reaction filtrate of Comparative Example 1) was 38.5%.

Comparative Example 3 When manganese acetate tetrahydrate and zirconyl acetate were not added in Example 1, oxygen absorption was stopped during the reaction, and the reaction yield of p-acetoxybenzoic acid was reduced to 29.5%. .

[0044]

According to the present invention, p-acetoxybenzoic acid can be obtained in high yield without coloring.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C07C 69/157 C07C 67/05

Claims (2)

(57) [Claims] 1. Acetylation and oxidation of p-cresol with a molecular oxygen-containing gas in an acetic acid solvent in the presence of acetic anhydride in the presence of a catalyst comprising a cobalt compound, a manganese compound, a zirconium compound and a bromine compound. A process for producing p-acetoxybenzoic acid. 2. The amount of acetic acid used is 0.5 to 7 times by weight based on p-cresol, the amount of acetic anhydride used is 1.8 to 7 times by weight based on p-cresol, and the amount of cobalt metal is used. The amount is 0.05 to 0.5 with respect to the total amount of acetic acid and acetic anhydride.
% By weight, the amount of Mn metal used is 0.
2 to 40% by weight, the amount of bromine atom used is 0.6 to 5 times by weight based on cobalt metal, and the amount of zirconium metal used is 7.5 to 30% by weight based on cobalt metal in the presence of a catalyst. The method for producing p-acetoxybenzoic acid according to claim 1, wherein the oxidation is performed.