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-sub stituted trans-cinnamic acids by pyridinium chlorochromate (PCC) in pr esence of oxalic acid has been studied. The main product of oxidation is corresponding benzaldehyde and glyoxalic acid. The reaction is firs t order with respect to [PCC] and [oxalic acid]. The oxidation follows fractional order in [substrate] and [H+]. The thermodynamic parameter s are also determined. Both the electron-releasing and electron-withdr awing 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 elec tron-withdrawing and carbonium ion for electron releasing substituents is discussed.