Process for purifying p-aminobenzoic

Claim 1

A PROCESS FOR DECOLORIZING P-AMINOBENZOIC ACID WHICH COMPRISES NEUTRALIZING AN AQUEOUS SOLUTION OF SAID ACID, ADDING A QUANTITY OF ACTIVATED CARBON VARYING BETWEEN FROM 5% TO 20% BY WEIGHT OF SAID P-AMINOBENZOIC ACID, HEATING SAID SOLUTION TO A TEMPERATURE RANGING BETWEEN 80* -90* C. UNDER A BLANKET OF NITROGEN, REMOVING SAID CARBON BY FILTRATION, ADDING A FURTHER QUANTITY OF SAID ACTIVATED CARBON IN THE AFORESAID AMOUNT TO THE FILTRATE FOLLOWED BY HEATING THE SOLUTION TO SAID TEMPERATURE UNDER BLANKET OF NITROGEN, FILTERING THE SOLUTION TO REMOVE THE ACTIVATED CARBON, COOLING THE FILTRATE AND THEN ADDING THERETO A QUANTITY OF A WATER-SOLUBLE, INORGANIC ALKALI METAL SULFITE IN AN AMOUNT VARYING BETWEEN 0.1-0.6% BASED ON THE WEIGHT OF P-AMINOBENZOIC ACID FOLLOWED BY INTRODUCING INTO THE RESULTING SOLUTION A FURTHER QUANTITY OF SAID ACTIVATED CARBON IN THE AFOREMENTIONED AMOUNT, FILTERING TO REMOVE THE CARBON THEN HEATING THE FILTRATE TO A TEMPERATURE OF ABOUT 80* C., THE AFOREMENTIONED DECOLORIZATION AND PURIFICARION STEPS BEING EFFECTED WITH THE SOLUTION AT A PH VARYING BETWEEN 5-7, AND ACIDIFYING THE SOLUTION FOLLOWED BY COOLING THEREOF TO OBTAIN P-AMINOBENZOIC ACID IN SUBSTANTIALLY PURE AND COLOR-FREE FORM.