KINETICS AND MECHANISM OF OXIDATION OF SOME SUBSTITUTED TRANS-CINNAMIC ACIDS BY PYRIDINIUM CHLOROCHROMATE - A NONLINEAR HAMMETT PLOT

Kinetics and mechanism of oxidation of some ortho-, para- and meta-substituted trans-cinnamic acids by pyridinium chlorochromate (PCC) in presence of oxalic acid has been studied. The main product of oxidation is corresponding benzaldehyde and glyoxalic acid. The reaction is first order with respect to [PCC] and [oxalic acid]. The oxidation follows fractional order in [substrate] and [H+]. The thermodynamic parameters are also determined. Both the electron-releasing and electron-withdrawing substituents, facilitate the rate of oxidation. Correlation with Hammett constants yields a 'V' shaped curve. A suitable mechanism is proposed. In the transition state the formation of carbanion, for electron-withdrawing and carbonium ion for electron releasing substituents is discussed.