|HYDANTOIN (glycolyl urea), C3H4N2O2 or CO||NH||·||CH2|
the ureïde of glycollic acid, may be obtained by heating allantoin or alloxan with hydriodic acid, or by heating bromacetyl urea with alcoholic ammonia. It crystallizes in needles, melting at 216° C.
When hydrolysed with baryta water yields hydantoic (glycoluric)acid, H2N·CO·NH·CH2·CO2H, which is readily soluble in hot water, and on heating with hydriodic acid decomposes into ammonia, carbon dioxide and glycocoll, CH2·NH2·CO2·H. Many substituted hydantoins are known; the α-alkyl hydantoins are formed on fusion of aldehyde- or ketone-cyanhydrins with urea, the β-alkyl hydantoins from the fusion of mono-alkyl glycocolls with urea, and the γ-alkyl hydantoins from the action of alkalis and alkyl iodides on the α-compounds. γ-Methyl hydantoin has been obtained as a splitting product of caffeine (E. Fischer, Ann., 1882, 215, p. 253).