- Oxyhalogen sulfur chemistry: Kinetics and mechanism of the oxidation of a Bunte salt 2-aminoethanethiolsulfuric acid by chlorite
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Spectrophotometric and 1H NMR methods have been used to study the kinetics and mechanism of oxidation of the Bunte salt, 2-aminoethanethiol sulfuric acid, H2NCH2CH2S-SO3H (AETSA) by chlorite in mildly acidic 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: 2ClO2- + H2NCH2CH2S-SO3H → ClNHCH2CH2SO3H + SO4-2 + Cl- + H+, while in excess AETSA the stoichiometry was: 3ClO2- + 2H2NCH2CH2S-SO3H + 2H20 → 2NH2CH2CH2SO3H + 2SO4-2 + 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 S-S 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 C-S bond. A 21-reaction kinetics scheme model gave reasonable agreement with experiment.
- Chinake,Mundoma,Olojo,Chigwada,Simoyi
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p. 4957 - 4964
(2007/10/03)
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- Antioxidant chemistry: Hypotaurine-taurine oxidation by chlorite
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Extensive experimental data have been collected on the oxidation of hypotaurine, H2NCH2CH2SO2H, by chlorite and chlorine dioxide. Hypotaurine is stable and reacts slowly with chlorite to give taurine, hypotaurine sulfonic acid, and monochloro- and dichlorotaurine. However, it reacts rapidly with chlorine dioxide with a second-order rate constant of 801 M-1 s-1 to give taurine. Oxidation occurs simultaneously at the sulfur center (to give the sulfonic acid) and at the nitrogen center (to give the chloramines). The stoichiometry of the reaction was experimentally determined to be ClO2- + H2NCH2CH2SO2H + H+ → ClHNCH2CH2SO3H + H2O. The formation of dichlorotaurine is favored only in high acid environments.
- Martincigh, Bice S.,Mundoma, Claudius,Simoyi, Reuben H.
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p. 9838 - 9846
(2007/10/03)
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