Electrochemical reduction mechanism of 2-thiouracil derivatives

Abstract

Abstract The mechanism of the polarographic reduction of 2-thiouracil and its S-methyl and ethoxy derivatives with stabilized 2-thiol-4-keto or 2-thione-4-enol structure has been studied. 2-Thiouracil is not electroreducible in aqueous solutions. However, it exhibits a strong tendency to adsorption and association on the mercury electrode. 2-Thio-4-ethoxypyrimidine undergoes a 4 e−, 4 H+ reduction which involves 2 e− reduction of the 3,4 NC bond, elimination of the ethoxy substituent to form 2-thiopyrimidine and 2 e−, 2 H+ reduction of the latter to 3,4-dihydroderivative. For 2-thiomethyluracil, a model compound of the 2-thiol-4-keto form, the electroactive centre is shifted to C-2 and in a 2 e−, 2 H+ reduction process the sulphur substituent undergoes elimination, to give pyrimidone-4; the latter can be further reduced at more negative potentials to tetrahydroderivatives (4 e− -process). Biological implications of these results have been discussed.