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Hippuric acid, or N-benzoylglycine, is an amino acid derivative found in the urine of herbivorous animals. The name is derived from Greek hippos (horse) and ouron (urine). In 1829, the pioneering German chemist Justus von Liebig so named it because his research on the compound concentrated on horse urine.
Hippuric acid also occurs in avocadoes (Persea americana) and common beans (Phaseolus vulgaris). As its chemical name suggests, the compound is formed by the reaction of benzoic acid and glycine in the urine.
Later in the 19th century, von Liebig’s last student, Oscar Loew, also studied hippuric acid. In 1879, Loew wrote about the source of the acid in herbivores’ urine. According to an account of the article in the first volume of the Journal of the American Chemical Society (1879), quinic acid1 in hay turns into hippuric acid during digestion. This finding had previously been observed in 1863 by Eduard Lautemann, a student of another important German chemist, Hermann Kolbe.
Synthetic hippuric acid is produced similarly to the biochemical reaction: Glycine is acylated with benzoyl chloride in the presence of base, followed by acidification to form the acid. Hydrolysis in strong base restores it to glycine and benzoic acid.
Extensive information about the biochemistry of hippuric acid and its implications for human health can be found in the ScienceDirect entry on the compound.
1. CAS Reg. No. 77-95-2.
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