1911 Encyclopædia Britannica/Hippuric Acid
HIPPURIC ACID (Gr. ἵππος, horse, οὖρον, urine), benzoyl glycocoll or benzoyl amidoacetic acid, C9H9NO3 or C6H5CO·NH·CH2·CO2H, an organic acid found in the urine of horses and other herbivorae. It is excreted when many aromatic compounds, such as benzoic acid and toluene, are taken internally. J. v. Liebig in 1829 showed that it differed from benzoic acid, and in 1839 determined its constitution, while in 1853 V. Dessaignes (Ann. 87, p. 325) synthesized it by acting with benzoyl chloride on zinc glycocollide. It is also formed by heating benzoic anhydride with glycocoll (Th. Curtius, Ber., 1884, 17, p. 1662), and by heating benzamide with monochloracetic acid. It crystallizes in rhombic prisms which are readily soluble in hot water, melt at 187° C. and decompose at about 240° C. It is readily hydrolysed by hot caustic alkalis to benzoic acid and glycocoll. Nitrous acid converts it into benzoyl glycollic acid, C6H5CO·O·CH2·CO2H. Its ethyl ester reacts with hydrazine to form hippuryl hydrazine, C6H5CO·NH·CH2·CO·NH·NH2, which was used by Curtius for the preparation of azoimide (q.v.).