Correlation Analysis of Reactivity in the Oxidation of Substituted Benzyl Alcohols by Benzyltrimethylammonium Dichloroiodate

Abstract

The oxidation of benzyl alcohol involves transfer of a hydride ion to a benzyltrimethylammonium dichloroiodate±zinc dichloride complex in the rate-determining step.Benzyltrimethylammonium polyhalides are widely used as halogenating reagents in synthetic organic chemistry. 1,2 We have recently reported the oxidation of phosphorus oxyacids by benzyltrimethylammonium dichloroiodate (BTMACI). 7 Here, we describe kinetics of oxidation of benzyl alcohol and thirty-two monosubstituted benzyl alcohols by BTMACI, in glacial acetic acid in the presence of zinc chloride. Mechanistic aspects are discussed.BTMACI was prepared by the reported method 1 and its purity was checked by an iodometric method. BTMACI is only slightly soluble in acetic acid at room temperature. However, addition of zinc chloride renders it readily soluble in acetic acid. The reactions were carried out under pseudo-®rst-order conditions by maintaining a large excess of the alcohol over BTMACI. The solvent was glacial acetic acid. The reactions were carried out in the presence of zinc chloride and were followed by monitoring the decrease in [BTMACI] iodometrically. The pseudo-®rst-order rate constant, k obs , was evaluated from the linear plots of log[BTMACI] vs. time. The experimental third-order rate constant, k 3 , was determined from the relationship:The oxidation of alcohols results in the formation of the corresponding aldehydes. The overall reaction may be represented as eqn. (1).