Electrochemical oxidation of 9-methylxanthine

The electrochemical oxidation of 9-methylxanthine proceeds via four voltammetric oxidation peaks at the pyrolytic graphite electrode. The first voltammetric oxidation peak (peak I_a) is a 1e reaction giving a radical which dimerizes to 8,8′-bi-9-methyl-9H-purine-2,6-(1H, 3H)-dione. Peak II_a is a further 2e electrooxidation of the peak I_a dimer to another yellow dimer 8,8′-bi-9-methyl-9H-purine-2,6-(1H)-dione-3,5-(3H)-diiminylidene. This dimer is not very stable and it hydrolyzes to 1-methyl allantoin. Peak III_a is an adsorption pre-peak to peak IV_a which corresponds, overall, to a direct 4e?4H⁺ electrooxidation of 9-methylxanthine to an unstable diimine of 9-methyluric acid. Hydrolysis of this diimine leads to a variety of ultimate products.