The Mechanism of Schiff Test for Uric Acid in Urine

Abstract

Uric acid in urine can be detected by reaction with silver nitrate in alkaline medium. A redox reaction occurs and black elemental silver is observed in the filter paper used in this test. However, the mechanism of the series of steps occurring in the uric acid molecule, including a second redox reaction, has not been advanced. A reaction route is provided, each step is fully commented giving also the electron flow. The mechanism involves free radicals and ionic intermediates as well. There is ring contraction with concomitant oxo-aziridine formation, imide hydrolysis, imine hydration to carbinol-amine, isomerization to ketone with concurrently ring opening, and assisted decarboxylation.