Para-aminobenzoic Acid
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
(p-Aminobenzoic Acid), H3NC6H4COOH 137.14 CAS RN®: 150-13-0.-White or slightly yellow crystals or crystalline powder, becoming discolored on exposure to air or light. One g dissolves in 170 mL of water, in 9 mL of boiling water, in 8 mL of alcohol, and in 50 mL of ether. Freely soluble in solutions of alkali hydroxides and carbonates; soluble in warm glycerin; sparingly soluble in diluted hydrochloric acid; slightly soluble in chloroform. Store in tight, light-resistant containers.
Assay: Accurately weigh about 300 mg, previously dried at 105° for 2 hours, and transfer to a beaker or casserole. Add 5 mL of hydrochloric acid and 50 mL of water, and stir until dissolved. Cool to about 15°, add about 25 g of crushed ice, and slowly titrate with 0.1 M sodium nitrite VS until a glass rod dipped into the titrated solution produces an immediate blue ring when touched to starch iodide paper. When the titration is complete, the endpoint is reproducible after the mixture has been allowed to stand for 1 minute. Each mL of 0.1 M sodium nitrite is equivalent to 13.71 mg of C7H7NO2. Not less than 98.5% is found.
MELTING RANGE (741): between 186° and 189°.
LOSS ON DRYING (731): Dry it at 105° for 2 hours: it loses not more than 0.2% of its weight.
Residue on Ignition (Reagent test): not more than 0.1%.
