1911 Encyclopædia Britannica/Alloxantin

ALLOXANTIN, C6H4N4O7.3H2O, a product obtained by the combination of alloxan and dialuric acid, probably possessing the constitution

NH—CO CO—NH
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CO C(OH) —O— CH  CO
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NH—CO CO—NH

one of the three molecules of water being possibly constitutional. It forms small hard prisms which become red on exposure to air containing ammonia, owing to the formation of murexide (ammonium purpurate), C6H4(NH4)N5O6. It may also be obtained by the action of sulphuretted hydrogen on alloxan. The tetra methyl derivative, amalic acid, C6(CH3)4N4O7, has been prepared by oxidizing caffeine (q.v.) with chlorine water, and forms colourless crystals which are only slightly soluble in hot water. The formation of murexide is used as a test for the presence of uric acid, which on evaporation with dilute nitric acid gives alloxantin, and by the addition of ammonia to the residue the purple red colour of murexide becomes apparent.