Oxyhalogen-sulfur chemistry: Kinetics and mechanism of the oxidation of a Bunte salt 2-aminoethanethiolsulfuric acid by chlorite

Spectrophotometric and H-1 NMR methods have been used to study the kinetics and mechanism of oxidation of the Bunte salt, 2-aminoethanethiol sulfuric acid, (AETSA) by chlorite in mildly acidic H2NCH2CH2S-SO3H media. The reaction is characterized by a long quiescent induction period followed by rapid and autocatalytic production of chlorine dioxide. The formation of chlorine dioxide is much more pronounced in stoichiometric excess of chlorite. The stoichiometry of the reaction in excess chlorite just before formation of chlorine dioxide was determined to be: 2ClO(2)(-) + H2NCH2CH2S-SO3H --> ClNHCH2CH2SO3H + SO4-2 + Cl- + H+, while in excess AETSA the stoichiometry was: 3ClO(2)(-) + 2H(2)NCH(2)CH(2)S-SO3H + 2H(2)O --> 2NH(2)CH(2)CH(2)SO(3)H + 2SO(4)(-2) + 3Cl(-) + 4H(+). Although the products in excess chlorite also included pure taurine and dichlorotaurine, monochlorotaurine was the dominant species at pH 1-3. This Bunte salt showed a facile SES bond cleavage after a single S-oxygenation step on the inner sulfur atom. The sulfoxide is quite stable but there was no experimental evidence for the existence of the sulfone-sulfonic acid. Sulfate production was almost quantitative for the oxidation of only one of the sulfur atoms. Further reaction of the taurine occurred only on the nitrogen atom with no cleavage of the CES bond. A 21-reaction kinetics scheme model gave reasonable agreement with experiment.