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Title: Mechanism of oxovanadium (IV)catalysed and uncatalysed bromate oxidation of lactic acid in acid medium: Evaluation of composite and individual kinetic and thermodynamic parameters
Authors: Reddy, Ch Sanjeeva
Kumar, T Vijaya
Issue Date: Nov-1999
Publisher: NISCAIR-CSIR, India
Abstract: Uncatalysed acid bromate oxidation of lactic acid (LA) exhibits fractional order (1.6) in [acid) and first order each in [Br(V)) and [LA]. Kinetic isotope effect (kH/kD=1) is absent, however an in verse solvent isotope effect (kH2O /  kD2O = 1.78 at 313 K) is observed. The mechanism proposed consists of a rate determining formation of bromate ester due to the nucleophilic attack by the alcoholic / hydroxyl group at the bromine atom of HOBrO2/ H2O22Br+O, followed by a fast disproportionation of the ester through C-C bond cleavage to form products. Oxovanadium(lV)-catalysed LA-Br(V) reaction exhibits second order in [acid], fraction al order in [lactic acid) and first order each in [VOSO4] and [oxidant]. The envisaged mechanism assumes a ternary complex formation involving a binary complex of LA and V(IV) and protonated bromate, which subsequently decomposes to the intermediate/products. The rate constants involved for each step of thc react ions are evaluated along with their thermodynamic parameters.
Page(s): 1188-1194
Appears in Collections:IJC-A Vol.38A(11) [November 1999]

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