Add time:09/06/2019         Source:sciencedirect.com

The kinetics and mechanism of oxidation of threose-series hexoses and pentoses by chloramine-T in alkaline medium was investigated. Kinetic studies with d-galactose, d-sorbose, d-xylose, and d-lyxose showed that the rate of the reaction was first order with respect to sugar and chloramine-T, and second order with respect to hydroxide ion. p-Toluenesulfonamide and chloride ions, the reduced products of chloramine-T, have no effect on the reaction rate. The rate increases with increase in ionic strength of the medium, and the dielectric effect is negative. Proton inventory studies in H2O–D2O mixtures suggested a single transition state. Product analysis for d-gulose, d-idose, l-sorbose, d-galactose, d-talose, d-tagatose, d-xylose, and d-lyxose revealed that all lyxose-series hexoses gave mainly mixtures of lyxonic and threonic acids with minor proportions of hexonic, xylonic and glyceric acids, whereas all xylose-series hexoses gave mixtures of lyxonic, threonic and glyceric acids with minor amounts of xylonic and hexonic acids. Xylose and lyxose gave mixtures consisting mainly of lyxonic, threonic, and glyceric acids with minor proportions of xylonic acid. From the results of kinetic studies, reaction stoichiometry, and product analysis, a possible mechanism for the oxidation of threose-series sugars with chloramine-T is suggested.

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