Kinetics and Mechanism of the Oxidation of some Hydroxy Acids by Imidazolium Fluorochromate

The oxidation of glycollic, lactic, malic and a few substituted mandelic acids by imidazolium fluorochromate (IFC) in dimethylsulphoxide (DMSO) leads to the formation of corresponding oxoacids. The reaction is first order each in IFC. Michaelies-Menten type of kinetics is observed with respect to the hydroxy acids. Reaction failed to induce the polymerisation of acrylonitrile. The oxidation of α-deuteriomandelic acid shows the presence of a primary kinetic isotope effect (kH/kD = 5.75 at 298 K). The reaction does not exhibit the solvent isotope effect. The reaction is catalysed by the hydrogen ions. The hydrogen ion dependence has the form: kobs = a + b [H+]. Oxidation of p-methyl mandelic acid has been studied in 19 different organic solvents. The solvent effect has been analysed by using Kamlet’s and Swain’s multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed.