Homogeneous catalysis of aquachlororuthenium(III) complex and evaluation of individual kinetic and thermodynamic parameters of bromate-mandelic acid reaction

Abstract

<span style="font-size:12.0pt;line-height:115%; font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:hi"="">Aquachlororuthenium(III) complex catalysed and uncatalysed acid bromate oxidation of mandelic acid (MA) is reported here. Uncatalyst oxidation exhibits first order each in [M A] and [bromate], and second order in [acid]. Primary kinetic isotope effect (<i>k</i>_H/<i>k</i>_D) = 1) has been found to be absent. However, an inverse solvent isotope effect is observed. The assumed mechanism includes slow formation of a mandelic ester of bromic acid due to the nucleophilic attack by the alcoholic/hydroxyl group at the bromine atom of HOBr⁺O(OH), which dissociates rapidly through C-C bond cleavage to form ben7.aldehyde and CO_2. Aquachlororuthenium(III) complex catalysed MA-bromate reaction exhibits second order in [bromated], first order in [catalyst], fractional order in [MA] and a dualistic effect in [acid]. The envisaged mechanism involves complex formation between the substrate and the catalyst, which in turn forms a ternary complex with two moles of the oxidant. The slow decomposition of the ternary complex to form products constitutes the rate-determining step. The rate constants involved in each step of the reaction have been <span style="font-size:12.0pt;line-height:115%;font-family:" times="" new="" roman";="" mso-fareast-font-family:hiddenhorzocr;mso-ansi-language:en-in;mso-fareast-language:="" en-in;mso-bidi-language:hi"="">evaluated <span style="font-size:12.0pt; line-height:115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:hi"="">along with their thermodynamic parameters.</span></span></span>