Oxyhalogen-sulfur chemistry: Non-linear oxidation of 2-aminoethanethiolsulfuric acid (AETSA) by bromate in acidic medium

The reaction between bromate and 2-aminoethanethiolsulfuric acid, H2NCH2CH2S-SO3H (AETSA), has been studied in high acid environments. The stoichiometry in excess AETSA is BrO3- + H2NCH2CH2S-SO3H + H2O --> H2NCH2CH2SO3H + SO42- + 2H(+) + Br-. In excess BrO3- the stoichiometry is: 7BrO(3)(-) + 5H(2)NCH(2)CH(2)S-SO3H --> 5Br(H)NCH2CH2SO3H + 5SO(4)(2-) + Br-2 + 3H(+) + H2O. The reaction displays clock reaction characteristics in which there is initial quiescence followed by a sudden and rapid formation of Br-2(a). The oxidation proceeds by successive addition of oxygen on the inner sulfur atom followed by cleavage of the S-S bond to form taurine and SO42-. The Br-2(aq) and the HOBr in solution oxidize the taurine to form a mixture of monobromotaurine and dibromotaurine. Computer simulations of a proposed 13-step reaction scheme produced st reasonable fit to the experimental data.