JPH03227956A - Production of p-hydroxybenzoic acid - Google Patents

Abstract

PURPOSE:To efficiently separate and purify the objective high-purity compound in separating the title compound from a reaction product of potassium phenolate and carbon dioxide, by acidifying the reaction product in an aqueous solution, heating and separating insoluble impurities under heating. CONSTITUTION:In separating the title compound useful as a raw material for polymer materials from a reaction product prepared by reacting potassium phenolate or a mixture containing the compound with carbon dioxide, the reaction product is acidified in an aqueous solution, the acidic aqueous solution is heated to dissolve the objective compound, insoluble impurities are separated under heating and the impurities in the reaction mixture are efficiently removed without using an expensive subsidiary raw material and a complicated device to give the high-purity objective compound advantageously. In crystallizing the objective compound from the aqueous solution prepared by acidification of the reaction product, preferably extracting operation under heating is carried out by using water in a sufficient amount to dissolve potassium salt of mineral acid precipitated during acidification.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for separating and purifying parahydroxybenzoic acid from a reaction mixture of potassium phenol or a mixture containing potassium phenol and carbon dioxide.

<Prior Art> Parahydroxybenzoic acid has a wide range of uses as a raw material for polymeric materials, and has recently attracted attention in particular as a raw material for liquid crystalline polyesters having high strength and high heat resistance.
Many of these alkyl esters are also useful substances as fungicides for cosmetics and industrial use.

Conventionally, as a method for producing parahydroxybenzoic acid, potassium phenol and carbon dioxide are reacted under high temperature and pressurized conditions in the presence or absence of a reaction medium.
The resulting mixture containing the potassium salt of para-hydroxybenzoic acid is treated with water and a water-insoluble organic medium (which may also be used as the reaction medium) to extract and separate the phenol into an organic layer. An aqueous solution containing the potassium salt of benzoic acid is obtained. A common method was to then add an acid to the aqueous solution to make it acidic, and then filter out the precipitated parahydroxybenzoic acid.

For example, Japanese Patent Publication No. 55-19207 proposes the following method. That is, in the presence of light oil, potassium phenol is reacted with carbon dioxide, and the product is
Cool to C. Next, the recrystallized mother liquor of parahydroxybenzoic acid generated in the lower step is added, and an oil layer and an aqueous layer are separated at 90°C. After extracting and removing by-product phenol from this aqueous layer with toluene and treating the aqueous layer with activated carbon, the pH was further lowered in two stages with sulfuric acid to crystallize potassium sulfate, parahydroxybenzoic acid, and salicylic acid in stages. analyze.

<Problems to be Solved by the Invention> However, in this method, a small amount of phenol and toluene are mixed into the aqueous layer. Further, in this method, the mother liquor of recrystallization of parahydroxybenzoic acid generated in the lower step is recycled, but this results in insufficient acid equivalent and unreacted potassium phenol remains. Since this potassium phenol is water-soluble, there are problems in that it cannot be removed during extraction with toluene.

In other patent examples, there are also problems such as tar-like substances generated during the reaction, impurities originally contained in raw materials, and potassium sulfate, which significantly reduce the color tone and purity of parahydroxybenzoic acid after acid precipitation. .

Patents related to such impurity removal include JP-A-48-
No. 28445 describes that, if necessary, precipitated impurities in the aqueous solution of the reaction mixture are filtered to remove the reaction medium and resinous substances. In addition, adsorption decolorization using activated carbon is also cited as a commonly used method.

Japanese Patent Publication No. 45-36497 describes a reductive decolorization purification method using zinc, but it is complicated due to equipment required for treatment with phosphoric acid, zinc, surfactants, etc., and waste liquid treatment due to the use of expensive heavy metals. , it is uneconomical.

As mentioned above, tar-like substances, reaction medium, phenol,
Regarding the removal of mineral acid potassium, conventional methods have problems such as the cost of auxiliary raw materials, the cost of equipment required for processing, and the complexity of handling the target material, as well as the fact that the color removal effect is not reliable. There is a problem.

Therefore, the present invention solves the above problems, efficiently removes by-products, reaction media, tar-like substances, and mineral acid potassium from the reaction mixture, and obtains industrially useful high-purity parahydroxybenzoic acid. The purpose is to provide a purification method.

Means for Solving the Problems> In order to solve the above-mentioned problems, the present inventors have made extensive studies and have completed the present invention.

That is, the present invention provides a method for separating parahydroxybenzoic acid from a product obtained by reacting potassium phenol or a mixture containing potassium phenol with carbon dioxide, which comprises acidifying the water-soluble portion of the product in an aqueous solution. , provides a method for producing para-hydroxybenzoic acid, which comprises heating the acidic water to dissolve para-hydroxybenzoic acid, and then separating insoluble impurities under heating.

Furthermore, when crystallizing para-hydroxybenzoic acid from the acidic water obtained by acidifying the product, a heating extraction operation is performed using a sufficient amount of water to dissolve the by-product mineral acid potassium precipitated during acidification. Good.

Hereinafter, the present invention will be explained in detail.

The reaction product which is a raw material in the present invention may be a reaction product obtained by reacting potassium phenol or a mixture containing potassium phenol with carbon dioxide. In particular, the higher the content of potassium parahydroxybenzoate salts in the reaction product, the easier the separation becomes, which is preferable.

Further, the reaction mixture obtained by the method described in Japanese Patent Application No. 63-259887 is also a raw material to which the method of the present invention can be effectively applied.

The reaction product which is the raw material of the present invention is obtained as a mixture containing parahydroxybenzoic acid potassium salts by reacting potassium phenol or a mixture containing potassium phenol as exemplified above with carbon dioxide.

In the present invention, the water-soluble portion of the reaction product is made into an aqueous solution. At this time, the parts that are insoluble or poorly soluble in water may be separated as they are by a liquid separation operation, or they may be extracted by adding an organic solvent that is insoluble or poorly soluble in water (which may also be used as the reaction medium). It may be liquid. The resulting aqueous solution is then acidified by adding a mineral acid.

The pH at this time is preferably 5 or less, more preferably 2 or less. This is because not only does the recovery rate of parahydroxybenzoic acid from an aqueous solution decrease when the pH is high, but also when tar acid is used as a raw material,
Since the tar component becomes difficult to separate and significant coloring is observed, it is best to adjust the temperature within this range.

The acid used in the present invention may be any mineral acid that is more acidic than parahydroxybenzoic acid and can liberate it, such as sulfuric acid, nitric acid, and hydrochloric acid.

Sulfuric acid is preferably used in terms of cost, corrosion, etc.

The content of parahydroxybenzoic acid in the aqueous solution after acidification is between 1% and 60%, preferably between 3% and 4%.
0%, more preferably between 4% and 20%. This is because a high concentration is preferable because it requires less heat, but the amount of water required for azeotropic distillation becomes insufficient. In addition, if the concentration is low, parahydroxybenzoic acid will be lost in the mother liquor after azeotropic distillation, and the yield will decrease. Just choose.

Next, in a heating extraction operation, this acidified aqueous solution (acidic water) is heated to dissolve parahydroxybenzoic acid, and then insoluble impurities remaining in the aqueous solution are separated under heating. Insoluble impurities herein refer to all impurities other than parahydroxybenzoic acid that are insoluble in hot acidic water.

Separation of insoluble impurities under heating consists of distillation removal of phenols and salicylic acids under heating, and subsequent or simultaneous separation of a hot solution and a solid insoluble in the hot solution.

The temperature at which insoluble impurities are separated under heating varies depending on the pH and other factors, and although it cannot be generalized, it is usually preferably boiling temperature; below this temperature, the effect of the present invention will not be sufficient, and if heated too much, This is not desirable because it causes phenomena such as bumping.

For example, methods such as filtration, decantation, and centrifugation are preferably used to separate the hot solution from the solid that is insoluble in the hot solution.

If the solution is heated sufficiently, phenols, organic solvents (if used for washing or as a reaction medium), and salicylic acids mixed in the solution are removed together with water or alone. One way to determine whether phenols and salicylic acids have been removed is to conduct a ferric chloride color reaction test on the distillate until no color is observed.

In addition, when potassium tar acid is used as a raw material as in the method described in Japanese Patent Application No. 63-259887, impurities thought to be derived from tar are dispersed in the crystals when the temperature of the solution is low. However, when the temperature is high (at high temperatures), the oil layer exists as an oil layer probably because it dissolves in the residual phenols in the solution, the residual reaction medium, and the residual washing organic solvent. By further heating this solution to boiling temperature, the oil layer It gradually disappears through boiling distillation, and impurities and cool substances generated during the reaction become a powdery solid.
Separation from hot solution becomes easy. The amount of water in the hot solution at this time should be at least the amount that dissolves the parahydroxybenzoic acid contained in the solution. In consideration of obtaining parahydroxybenzoic acid, it is preferable to use enough water to dissolve inorganic impurities such as potassium mineral acid in the cooled aqueous solution. If this amount or more,
Although the yield of parahydroxybenzoic acid decreases accordingly, the amount of mineral acid potassium mixed in parahydroxybenzoic acid also decreases, so a suitable amount is selected around this range. For this solid-liquid phase separation, methods such as filtration, decantation, and centrifugation are appropriately selected.

<Example> The present invention will be specifically described below with reference to Examples.

(Example 1) Phenol potassium and carbon dioxide were reacted in the presence of light oil, and the resulting reaction product was 39.9 g (dipotassium parahydroxybenzoate 9.61 g, potassium salicylate 0.20 g, phenol potassium 0.77 g) , 4.23 g of phenol) was dissolved in 150 cc of water, separated at 60° C., and the aqueous solution was washed twice with 30 cc of toluene. 1. Add ON sulfuric acid to the obtained aqueous solution and
Acidified to H2.

This solution was heated on a pot plate at 120° C. for 30 minutes, and the phenol, toluene, and salicylic acid were distilled out along with water through a side tube attached to the flask, and the hot solution was filtered while hot.

At this time, the weight of the distillate was 60 g, and during hot filtration, the weight was 0.
．． 1 g of insoluble impurities were filtered off. The resulting solution was cooled to precipitate crystals of para-hydroxybenzoic acid, and then filtered to obtain 5.1 g of para-hydroxybenzoic acid (purity 99%).

The potassium content in this parahydroxybenzoic acid is 0
．． It was 58%. The components of the distillate from the side tube are:
Phenol O, Log, toluene 4g, salicylic acid 3.
2 mg, and no parahydroxybenzoic acid was detected.

(Example 2) Potassium tar acid, obtained by converting tar acid obtained from coal and cool into potassium chloride with potassium hydroxide, was reacted with carbon dioxide in the presence of light oil to produce a reaction product 40.
2g (7.10g dipotassium parahydroxybenzoate
, potassium salicylate 0. Log, phenol potassium 0.16g, phenol 0.49g, cresols 2.
80 g) was dissolved in 150 cc of water, separated at 60° C., and the aqueous solution was washed twice with 30 cc of toluene to obtain an aqueous solution containing tar. This aqueous solution was acidified to 2 pH H2 by adding ION sulfuric acid. This solution was heated on a hot plate at 120'C for 30 minutes, and phenol, cresols, toluene, and salicylic acid were distilled out along with water from a side tube attached to the flask, and then filtered while hot. At this time, the weight of the distillate was 70 g, and 1.2 g of insoluble impurities were filtered out during hot filtration.

The resulting solution was cooled to precipitate crystals of parahydroxybenzoic acid, and then filtered to obtain 4.6 g of parahydroxybenzoic acid (purity 97%). The potassium content in this parahydroxybenzoic acid was 0.79%.
The distillate from the side pipe contains 0.06 g of phenol.
, 3 g of toluene, and 3.5 mg of salicylic acid, and no parahydroxybenzoic acid was detected.

<Effects of the Invention> According to the present invention, impurities in a potassium parahydroxybenzoate mixture can be efficiently removed without using expensive auxiliary raw materials or complicated equipment in an industrially useful separation and purification method for parahydroxybenzoic acid. Is possible. When raw materials containing many high-boiling point impurities are used, these impurities can be easily separated as solids, which is of great benefit to industry in terms of effective utilization of the raw materials.

1, -ノ (knee·'

Claims (2)

[Claims] (1) In a method for separating parahydroxybenzoic acid from a product obtained by reacting phenol potassium or a mixture containing phenol potassium with carbon dioxide,
A method for producing para-hydroxybenzoic acid, which comprises acidifying the product in an aqueous solution, heating the acidic water to dissolve para-hydroxybenzoic acid, and then separating insoluble impurities under heating. (2) When crystallizing parahydroxybenzoic acid from the acidic water obtained by acidifying the product, a heating extraction operation is performed using a sufficient amount of water to dissolve potassium mineral acid, a by-product, which is precipitated during acidification. The method for producing parahydroxybenzoic acid according to claim 1.