RU2594480C1 - Method of purifying para-aminobenzoic acid - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of purifying para-aminobenzoic acid. Method involves dissolving, treating solution while heating with activated carbon and sodium bisulphite, cooling solution with extraction of crystals of para-aminobenzoic acid, filtration thereof, washing and drying. Method is characterised by that extracted para-aminobenzoic acid is dissolved in ethyl alcohol at temperature of 20-35 °C to concentration of 1-10 wt%, then solution is filtered from insoluble impurities and while stirring adding activated carbon in mixture with aluminium oxide in weight ratio of 1:1 in an amount of 10-30 wt% of weight of para-aminobenzoic acid. Obtained mixture is held at temperature 60-80 °C for 20-60 minutes, then mixture is filtered, 3/4 is of weight of ethyl alcohol is distilled from filtrate, water is added, sodium bisulphite in amount of 0.01-0.3 wt% of weight of para-aminobenzoic acid and distillation of water-alcohol azeotrope is continued. Then solution is cooled to 5-25 °C, para-aminobenzoic acid crystals precipitated at this temperature crystals are filtered, washed with water and dried.

EFFECT: disclosed method enables to obtain para-aminobenzoic acid with high degree of purity and reduction of its losses during cleaning.

1 cl, 1 tbl, 23 ex

Description

The invention relates to the chemical industry, and in particular to a method for purifying para-aminobenzoic acid used in the synthesis of pharmaceuticals, dyes, antioxidants, developers, polymers and other products.

The authors of the invention had the task of obtaining para-aminobenzoic acid of high purity. It was necessary to develop a method for acid purification, which provides a product with a basic substance content of at least 99.5%, a melting point of 187-189 ° C and a residue value after calcination in the form of sulfates of not more than 0.05 wt. %

The evidence of the presence of an undesirable amount of impurities in para-aminobenzoic acid is a mismatch with the values of the above physicochemical parameters.

A known method of purification of para-aminobenzoic acid by recrystallization from water ("Preparative organic chemistry" under the editorship of NS Wulfson. M., Goskhimizdat, 1959, S. 554). Para-aminobenzoic acid is dissolved with stirring and heating to 80-90 ° C with activated carbon and sodium hydrosulfite in water. The hot solution is separated from coal and cooled to 5-10 ° C, the precipitated crystals of para-aminobenzoic acid are filtered off, washed and dried. The para-aminobenzoic acid purified by this method has a basic substance content of 98.5 wt.%, A melting point of 185 ° C, a residue after calcination of 0.3 wt.%, A yield of 80.0 wt.%. These indicators do not meet the above requirements for the physicomechanical properties of para-aminobenzoic acid and indicate the presence of a significant amount of impurities in it.

There is also a known method for purifying para-aminobenzoic acid according to RF patent No. 2304576, published on 08/20/2007. The cleaning method includes treating the extracted para-aminobenzoic acid with sodium hydrosulfite and charcoal when heated to 80-90 ° C, filtering the hot solution from coal, cooling the filtrate to 5-10 ° C, separation of the precipitated precipitate of para-aminobenzoic acid, washing it with cold water and drying at 50-60 ° C. Get para-aminobenzoic acid - a white crystalline powder with so pl. 187-188 ° C, the basic substance content of 99.8-99.9%, the residue after calcination in the form of sulfates of 0.006-0.01%. This method relates to the purification of para-aminobenzoic acid obtained by hydrogenation of para-nitrobenzoic acid with hydrogen. When using this method for the purification of para-aminobenzoic acid obtained in another way, for example, by reducing para-nitrobenzoic acid with hydrazine hydrate, such high purity and yield values cannot be achieved. The content of the basic substance is 97.4 wt.%, The melting point is 185 ° C, the residue after calcination is 0.07 wt.%, The yield is 92.0 wt.%.

The prototype of the invention is a method for purifying aminobenzoic acids according to the USSR author's certificate No. 5686164, published on 12.30.77. The author's certificate claims a method for the isolation and purification of aminobenzoic acids by acidifying a solution of alkaline salts of para-aminobenzoic acid with hydrochloric acid to pH 4-5, followed by treatment suspensions when heated to 80-90 ° C with charcoal and sodium hydrosulfite. The hot solution is filtered off from coal, cooled, crystals of para-aminobenzoic acid precipitated are separated, washed with water and dried. Get para-aminobenzoic acid with so pl. 185-188 ° C, the residue after calcination is 0.02-0.03%, the content of the main substance is 99.8-99.9%. The yield of para-aminobenzoic acid is 92-94%. This method also relates to the purification of para-aminobenzoic acid obtained by hydrogenation of para-nitrobenzoic acid with hydrogen. The purification of para-aminobenzoic acid obtained in a different way, for example, by reducing para-nitrobenzoic acid with hydrazine hydrate, does not allow to achieve the necessary indicators for purity and yield. The content of the basic substance is 98.9 wt.%, The melting point is 186 ° C, the residue after calcination is 0.07 wt.%, The yield is 91.2 wt.%.

The aim of this invention is to develop a method for purification of para-aminobenzoic acid, which would allow to obtain a product with a high degree of purity and its least loss during the cleaning process. The developed method should be used for purification of para-aminobenzoic acid obtained by any method.

The problem is solved by a method for purifying para-aminobenzoic acid, in which the extracted para-aminobenzoic acid is dissolved in ethyl alcohol at a temperature of 20-35 ° C to a concentration of 1-10 wt.%, Then it is filtered off from insoluble impurities and activated carbon and aluminum are added with stirring oxide in a ratio of 1: 1 in an amount of 10-30 wt.% by weight of para-aminobenzoic acid, the mixture is kept at a temperature of 60-80 ° C for 20-60 minutes. Next, the mixture is filtered, ¾ mass of ethyl alcohol is distilled off from the filtrate, water and sodium hydrosulfite are added in an amount of 0.01-0.3 wt.% By weight of para-aminobenzoic acid, and the distillation of the water-alcohol azeotrope is continued. Upon completion of the distillation of ethyl alcohol, the solution is cooled to 5-25 ° C. The crystals of para-aminobenzoic acid that precipitated at this temperature are filtered off, washed with water and dried.

To implement the method of purification of para-aminobenzoic acid, the following substances are used:

raw para-aminobenzoic acid - technical rectified ethyl alcohol GOST 18300-87 chromatographic aluminum oxide "h" TU 6-09-3916-75 activated carbon brightening wood GOST 4453-74 sodium hydrosulfite GOST 246-76 distilled water GOST 6709-72

The invention is illustrated by the following examples of specific performance.

Example 1

Para-aminobenzoic acid (p-ABA) obtained by catalytic reduction of para-nitrobenzoic acid (p-NBA) with hydrazine hydrate in an amount of 10.0 g (basic content of 96.0 wt.%) Is placed in a reactor equipped with a stirrer and a thermometer, and dissolved with stirring at a temperature of 20-35 ° C in 100 g of ethyl alcohol. An alcohol solution through a double paper filter is filtered off from insoluble impurities. The filtrate is poured into a reactor equipped with a stirrer, a thermometer and a reflux condenser, 1.5 g (15.0 wt.%) Alumina, 1.5 g (15.0 wt.%) Activated carbon are added and the mixture is heated under vigorous stirring at a temperature of 60 ° C for 20 minutes. Then the solution is separated (via a double paper filter) from the spent adsorbent and the filtrate is poured into the reactor of the ethanol distillation apparatus at atmospheric pressure. After distillation at a bath temperature of 100 ° C, 3/4 of the solvent mass is added to the reactor 40 g of distilled water and 0.01 g (0.1 wt.%) Sodium hydrosulfite and water-alcohol azeotrope is continued to be distilled off. Upon completion of the distillation of ethyl alcohol, the hot solution is poured into a beaker in which p-ABA crystals precipitate upon cooling to 5-25 ° C. The purified product is filtered off, washed with water and dried to constant weight in a vacuum oven at a temperature of 80 ° C.

Obtain 9.0 g of p-ABA with a basic substance content of 99.8 wt.%, A melting point of 188 ° C and the value of the residue after calcination of 0.02 wt.%. Yield 93.8 wt.%.

Example No. 2-8 (according to the invention)

The method of isolation and purification of p-ABA according to example No. 1, only the conditions for the purification are changed. Concentration and temperature-time parameters of the modes of purification of p-ABA from impurities, the yields of purified products and their physicochemical parameters are presented in the table.

Example No. 9 of the prototype.

167 g (0.1 mol) of p-ABA obtained by catalytic reduction of p-NBA with hydrazine hydrate was isolated by filtering the reaction mixture from the catalyst and acidifying the filtrate with 20.0 wt.% Hydrochloric acid to pH 4-5 with stirring. To a suspension of precipitated p-ABA in water add 30 g of activated carbon, 0.3 g of sodium hydrosulfite and the mixture is heated to 80-90 ° C with stirring and holding for 30 minutes. The hot solution is filtered from coal, and after cooling the filtrate, the precipitated p-ABA precipitate is separated, washed with water and dried to constant weight in a vacuum oven at 80 ° C.

Get 124.9 g of p-ABA with a basic substance content of 98.9 wt.%, A melting point of 186 ° C, the residue after calcination of 0.07 wt.%. The yield of p-ABA is 91.2 wt.%.

Examples No. 10-17 (for comparison)

The method of isolation and purification of p-ABA according to example No. 1, only the conditions for the implementation of the method change. Concentration and temperature-time parameters of the modes of purification of p-ABA from impurities, the yields of purified products and their physicochemical parameters are presented in the table.

Examples No. 18-23 for comparison

The method of isolation and purification of p-ABA according to example No. 1, only the conditions for the implementation of the method outside the claimed. Concentration and temperature-time parameters of the modes of purification of p-ABA from impurities, the yields of purified products and their physicochemical parameters are presented in the table.

The data presented in the table show that the values of the physicochemical parameters of p-ABA samples purified by the claimed method correspond to a content of the main substance of 99.5-99.9 wt.%, A melting point of 187.5-188.1 ° С and a value the residue after calcination in the form of sulfates of 0.01-0.03 wt.%, which indicates the conformity of their quality to the requirements. The yield of p-ABA after isolation and purification is 93.8-95.1 wt.%. These indicators exceed the readings of the prototype, which are 98.9 wt.%, 186 ° C, 0.07 wt.% And a yield of 91.2 wt.%, Respectively (see examples No. 1-8 in comparison with No. 9).

In the method proposed by the authors for purification of para-aminobenzoic acid, a mixture of adsorbents is used, namely, a mixture of activated carbon with aluminum oxide in an amount of 10.0-30.0 wt.% By weight of para-aminobenzoic acid with a mass ratio of 1: 1 (see examples No. 1-8). When using activated carbon or aluminum oxide in the same amount as their mixture, this degree of purification cannot be achieved. The content of the basic substance is lower and amounts to 98.0-99.0 wt.%, The residue after calcination is 0.07-0.08 wt.%, Which is 2.3-8 times higher than the product purified by the claimed method. An insufficient degree of purification is also indicated by the melting point of purified para-aminobenzoic acid, which is 185.0-185.5 ° С, and 187-189 ° С is required (see examples Nos. 1-8 in comparison with Nos. 10-13 .)

With the exception of the method of purification of para-aminobenzoic acid sodium hydrosulfite, a product is obtained that darkens in the light (see examples No. 14-15)

Examples No. 16-17 show that without the use of adsorbents, para-aminobenzoic acid of the required purity cannot be obtained.

The implementation of the method of purification of p-ABA under conditions outside the declared, for example, the use of p-ABA for cleaning less than 10 wt.% A mixture of aluminum oxide and coal (example No. 18), heating an alcohol solution of p-ABA with adsorbents at a temperature below 60 ° C ( example No. 20) and during a time period of less than 20 minutes (example No. 21), it does not allow to completely clean p-ABA from impurities, as evidenced by obtaining samples with a low content of the basic substance, inappropriate melting temperature and an increased value of the residue after calcination.

Using for cleaning alcohol solutions of p-ABA with a concentration below 1 wt.% Is impractical, since the low content of the basic substance is accompanied by significant losses during the cleaning process and unreasonable consumption of solvent and adsorbents.

It is shown that when p-ABA is used for the purification of alcohol solutions having a concentration above 10 wt.% (Example No. 19), incomplete acid solubility in ethanol is observed, which leads to significant losses of the target product.

It was also found that the use of more than 30 wt.% Adsorbents for cleaning p-ABA, heating an alcohol solution with activated carbon and aluminum oxide at a temperature above 80 ° C and for a time period of more than 60 minutes is not advisable, since it does not lead to a further increase purity levels of p-ABA.

The implementation of the method when dissolving para-aminobenzoic acid in another solvent, for example in water, does not allow to achieve the necessary indicators of the degree of purity (see examples No. 22-23 in comparison with No. 1-8).

The desired effect on the purity of para-aminobenzoic acid is achieved by a combination of all the features set forth in the claims. The exclusion of at least one of the signs or going beyond the stated conditions for the purification does not give the desired result in terms of purity and yield after cleaning.

Claims (1)

A method for purifying para-aminobenzoic acid, including dissolving it, treating the solution with activated carbon and sodium hydrosulfite, cooling the solution to isolate crystals of para-aminobenzoic acid, filtering, washing and drying, characterized in that the extracted para-aminobenzoic acid is dissolved in ethyl alcohol at a temperature of 20-35 ° C to a concentration of 1-10 wt.%, then the solution is filtered off from insoluble impurities, and with stirring, activated carbon in a mixture with aluminum oxide is added when they are a weight ratio of 1: 1 in an amount of 10-30 wt.% by weight of para-aminobenzoic acid, the mixture is kept at a temperature of 60-80 ° C for 20-60 minutes, then the mixture is filtered, 3/4 of ethanol is distilled off from the filtrate, add water, sodium hydrosulfite in an amount of 0.01-0.3 wt.% by weight of para-aminobenzoic acid and continue distillation of the water-alcohol azeotrope, then the solution is cooled to 5-25 ° C, crystals of para-aminobenzoic acid precipitated at this temperature filtered off, washed with water and dried.