1911 Encyclopædia Britannica/Allantoin

ALLANTOIN, C4H6N4O3 or CO	NH – CH – NH – CO – NH2	, the diureide of glyoxylic acid.
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	NH – CO

It is found in the allantoic liquid of the cow, and in the urine of sucking calves. It can be obtained by the oxidation of uric acid by means of lead dioxide, manganese dioxide, ozone or potassium permanganate:

C₅H₄N₄O₃ + H₂O + O＝C₄H₆N₄O₃ + CO₂.

It has been synthesized by E. Grimaux by heating one part of glyoxylic acid with two parts of urea for ten hours at 100° C.: 2CO(NH₂)₂ + CH(OH)₂COOH＝3H₂O + C₄H₆N₄O₃. It forms glancing prisms of neutral reaction slightly soluble in water. On standing with concentrated potassium hydroxide solution it gives potassium allantoate C₄H₇N₄O₄K. On heating with water it undergoes hydrolysis into urea and allanturic acid C₃H₄O₃N₂. It is reduced by sodium amalgam to glycouril C₄H₆N₄O₂, whilst with hydriodic acid it yields urea and hydantoin C₃H₄N₂O₂. Hot concentrated sulphuric acid also decomposes allantoin, with production of ammonia, and carbon monoxide and dioxide. By dry distillation it gives ammonium cyanide.