METHOD OF PURIFYING PARA-AMINOBENZOIC ACID Russian patent published in 2016 - IPC C07C227/40 C07C227/42 C07C229/60 

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