The desolvation and oxidation of crystals of dialuric acid monohydrate

Examination of the influence of the solvent of crystallization on the solid-state oxidation of dialuric acid (I) monohydrate to alloxantin (II) is reported. This reaction was investigated at low and high humidities using photomicrography, X-ray crystallography, and IR and mass spectrometry. Crystals of dialuric acid desolvated somewhat anisotropically; this behavior was consistent with crystal packing. The desolvated crystals of dialuric acid monohydrate had approximately the same crystal structure as the monohydrate and were stable in air at room temperature at low humidities. At high humidity, these crystals rehydrated and rapidly oxidized to alloxantin. These studies showed for the first time that desolvation was not a necessary prerequisite to solid-state oxidation and that solid-state oxidation reactions could be accelerated by high humidity.