Kinetics and mechanism for reduction of tetrabromoaurate(III) by uridine

Abstract

The reaction of tetrabromoaurate(III) with uridine in water occurs with a 1 : 1 stoicheiometry, producing gold(I) and 5-bromo-6-hydroxy-5,6-dihydrouridine. The reduction of AuBr₄^–, studied in the presence of uridine, bromide, and acid in excess with respect to gold, and in some cases also in the presence of added reaction products, obeys the rate expression –d[AuBr₄^–]/dt =k_obs,[AuBr₄^–]/([Au]_T–; [AuBr₄^–]), where [Au]_T is the total gold concentration ([Au^III]+[Au^I]). The rate k_obs, is linearly dependent on the uridine concentration and invariant of the bromide and hydrogen-ion concentrations. The observed redox kinetics are consistent with a mechanism involving reductive elimination of bromine from tetrabromoaurate(III) followed by halogenation of the pyrimidine.