Oxidation of Diols by Morpholinium Fluorochromate: A Kinetic and Mechanistic Study

Abstract

The kinetics of oxidation of diols by morpholinium fluorochromate (MFC) has been studied in dimethyl sulfoxide (DMSO). Corresponding hydroxy carbonyl compounds are the main product of oxidation. The reaction is first order in MFC and follows Michaelis-Menten type of kinetics with respect to diols. The reaction is catalyzed by H+ ions. The hydrogen ion dependence has the form: kobs =a+ b[H+]. Oxidation of deuterated ethylene glycol showed substantial primary kinetic isotopic effect (kH / kD = 5.750 at 298 K). Thermodynamic parameters like enthalpy, entropy and free energy of activation are discussed and validity of the isokinetic relationships also established. We have used nineteen different organic solvents for carrying out our analysis. Taft and Swain’s multiparametric equations have been used for the solvent effect analysis. In our experiments rate constants have showed excellent correlation with Taft's Σσ* values along with negative values for the reaction constant ρ*. A suitable mechanistic pathway for the chromate ester formation has also been suggested.