1911 Encyclopædia Britannica/Alloxan

ALLOXAN, or Mesoxalyl Urea, C₄H₂N₂O₄ or

CO

NH—CO NH—CO

CO.

an oxidation product of uric acid, being obtained from it by the action of cold nitric acid, C₆H₄N₄O₃ + H₂O + O = C₄H₂N₂O₄ + CO(NH₂)₂. It crystallizes from water in colourless rhombic prisms, containing four molecules of water of crystallization, and possesses a very acid reaction. It serves as the starting-point for the preparation of many related substances. Zinc and hydrochloric acid in the cold convert it into alloxantin (q.v.), hydroxylamine gives nitroso-barbituric acid, C₄H₂N₂O₃:NOH, baryta water gives alloxanic acid, C₄H₄N₂O₅, hot dilute nitric acid oxidizes it to parabanic acid (q.v.), hot potassium hydroxide solution hydrolyses it to urea and mesoxalic acid (q.v.) and zinc and hot hydrochloric acid convert it into dialuric acid, C₄H₄N₂O₄. M. Nencki has shown that alloxan combines with thiourea in alcoholic solution, in the presence of sulphur dioxide to form pseudothiouric acid, C₅H₆N₄SO₃. Methyl and dimethylalloxans are also known, the former being obtained on oxidation of methyl uric acid, and the latter on oxidation of caffeine (q.v.).