Kinetics and Mechanism of Oxidation of Benzoin and its Derivatives by Acid-Dichromate

Department of Chemistry, Ravenshaw College, Cuttack-753 003

Manuscript received 7 February 2978, accepted 2 November 1979

The kinetics of oxidation of benzoin and substituted benzoins by acid dichromate have been investigated in acetic acid water mixture. The reaction shows first order dependence on the concentrations of both Cr(VI) and substrate. The reaction is acid catalysed and the order with respect to sulphuric acid concentration is two. The reaction rate is not affected by changing the concentrations of both sulphate and bisulphate ions. HCrO^{${}_3^{+}$} is considered to be the active oxidant. Evidence for the complex formation between the oxidant and the substrate has been indicated. The order of reactivity in different mineral acids follows the sequence : HClO₄>H₂SO₄>HCI. Addition of Mn(II) retards the rate of the reaction considerably. Activation parameters have been evaluated and structure-reactivity relationships discussed. The results are accommodated by considering the reaction to take place between enol form of the ketone and the oxidant via Cr(VI)-ester which subsequently decomposes in the rate determining step to give the product.