Abstract
The reaction between brómate and thiourea has been studied in acidic medium. At the end of the induction period, the redox potential of the reaction mixture rises sharply, sulfate appears (signaled by precipitation of BaS04 when BaCl2 is initially added), and a yellow coloration (due to bromine) is first noticeable. Consequently, bromine is not formed until all thiourea is consumed. A 14-step mechanism is proposed and used to simulate the observed kinetics. The rate-determining step for bromine appearance is formation of HOBr from the Br03 -Br~ reaction. The oxidation of thiourea proceeds via oxygen additions on
sulfur, successively forming HOSC(NH)NH2, H02SC(NH)NH2, H03SC(NH)NH2), and S042". The mechanism requires that cleavage of the X-C bond to form urea and S042- occur at the sulfonic acid level and not before, in agreement with experimental observation.