The Mechanism of Frabot Test for Uric Acid

Uric acid is an Analyte. Excess uric acid ─ hyperuricemia ─ leads to gout and renal stones. Frabot noted that uric acid added to an alkaline tungstate solution developed an intense blue colour. A colorimetric method widely utilized to quantify uric acid depends on the reduction of the chromogen sodium tungstate by uric acid to produce a measurable colour change. The reaction route from the initial products to the coloured compounds and the oxido-degradation of the organic substance has not been advanced. In this communication the electron flow is given in each step of the series of reactions that take place. These are isomerization to imidol, Michael addition to enone, oxirane formation in a redox step, hydrolysis of imido group, oxirane ring opening, ring contraction to five- member ring, ring opening via alkoxide, and finally assisted decarboxylation to the end product, 5-ureido hydantoin (allantoin).