Abstract

K. Bijudas

DOI : http://dx.doi.org/10.13005/ojc/300360

Kinetics of the oxidation of benzyl alcohol and some of its para substituted derivatives by acidified dichromate has been studied in acetic acid – water medium. The reaction showed first order dependence on both [substrate] and [oxidant]. The reaction failed to induce the polymerisation of added acrylonitrile and this rules out the involvement of any radical intermediate in the reaction. The reaction was found to be acid catalysed and showed fractional dependence on [acid].  The order of reactivity among the studied benzyl alcohols is   p - OCH₃ > p - CH₃ > - H > p – Cl > p – NO₂.  Plots of log k₂ versus Hammett's substituent constant (s) has been found to be curve shaped and this suggests that there should be a continuous change in transition state with changes in substituent present in the substrate from electron donating to electron withdrawing. Thermodynamic parameters were determined and a suitable mechanism is proposed in concordance with the obtained results.

Acidified dichromate; benzyl alcohol; kinetics; mechanism; selective oxidation; substituted benzyl alcohols

[ View HTML Full Text]