Abstract
The murexide test used for identification of uric acid is mentioned in many laboratory texts. It consists in the degradative oxidation of uric acid by means of nitric acid and then a combination to yield a two ring product, purpuric acid. This gives a purple colour on addition of ammonia. From the chemical structure of the final product, various compounds are known to intervene for its obtention. However, the course of their formation during the degradation-oxidation process has not been cleared up. Thus, a mechanistic approach has been provided, step by step, in order to clarify the reaction sequence until the end product. Other compounds also formed are treated too. The study is based on well known reactivities and experimental observations.
Highlights
The murexide test for uric acid consists in the reaction of uric acid with dilute nitric acid, followed by ammonia addition: a purple colouration is produced due to the formation of ammonium purpurate or murexide
Alloxantin, the hemiketal formed between alloxan and dialuric acid has been prepared by partial reduction of alloxan with hydrogen sulphide, [16,17]
The mechanism of the degradative oxidation of uric acid to murexide by means of nitric acid and ammonia has not been studied and we provide it
Summary
The murexide test for uric acid consists in the reaction of uric acid with dilute nitric acid, followed by ammonia addition: a purple colouration is produced due to the formation of ammonium purpurate or murexide. The reaction mixture is heated to dryness in a porcelain dish on the water bath. Murexide was used as a dye for wool, and the uric acid was isolated from guano. Urea and parabanic acid are formed in the dye synthesis. The reaction mechanism of murexide formation has not been studied. We considered of interest to clear up the reactivities involved, continuing our studies on reaction mechanisms [6,7,8,9,10]
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