1911 Encyclopædia Britannica/Allantoin

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

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.