Correlation analysis of reactivity in the oxidation of substituted benzylamines by pyridinium hydrobromide perbromide

Department of Chemistry, J. N. Y. University, Jodhpur-342 001, India

E-mail: seema@goraexports.com; gora@datainfosys.net

Manuscript received 9 February 2004, accepted 11 June 2004

The oxidation of henzylamine and twenty-seven ortho-, meta- and para-substituted benzyIamines by pyridinium hydrohromide perbromidc (PHPB), in dimethylsulphoxide (DMSO), leads to the formation of the corresponding aldimines. The reactions are of first order with respect to both PHPB and the amine. The oxidation of deuterated benzylamine exhibited a substantial kinetic isotope effect ( k_H/k_D = 3.20 at 303 K). An addition of pyridinium bromide docs not affect the rate. PHPB itself has been postulated as the reactive oxidizing species. The rates of the oxidation of para- and meta-substituted benzylamines were correlated with Taft's and Swain's field and resonance substituent constants. The oxidation of para-substituted benzylamines showed an excellent correlation with Taft's σ₁ and \(\sigma_R^{BA}\) values; the me/a-compounds correlated best with σ₁ and σ_R⁰ values. Rates of the ortho-substituted compounds showed a significant correlation with Charton's triparamctric equation. Suitable mechanism has been proposed.