KINETICS AND MECHANISM OF RUTHENIUM(III) CATALYZED OXIDATION OF SECONDARY ALCOHOLS BY BROMAMINE-T IN HYDROCHLORIC ACID SOLUTIONS

ABSTRACT

The kinetics of oxidation of 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, and 2-heptanol by sodium N-bromo-p-toluenesulfonamide (bromamine-T or BAT) to the corresponding ketones in the presence of HCl and catalyzed by ruthenium(III) chloride has been studied at 30 °C. The reaction rate shows a first-order dependence on [BAT] and a fractional-order each on [alcohol], [Ru(III)] and [H⁺]. Addition of the reaction product, p-toluenesulfonamide, retards the rate. An increase in the dielectric constant of the medium decreases the rate. Variations of ionic strength and halide ion concentration have no effect on the rate. Rate studies in D₂O medium show that the solvent isotope effect, k′_(H2O)/k′_(D2O), equals 0.67. Proton inventory studies were carried out using H₂O-D₂O mixtures. Attempts have been made to arrive at a linear free-energy relationship through the Taft treatment and observed that the rate constants do not correlate satisfactorily. An isokinetic relationship is observed with β=354K indicating that enthalpy factors control the rate which is also confirmed by the Exner criterion. A mechanism consistent with the observed kinetics has been proposed and discussed.

ACKNOWLEDGMENT

One of us (R.R.) thanks the Principal and the Management of Jyothi Nivas College, Bangalore, India, for granting permission to perform graduate research in the Department of Post-Graduate Studies in Chemistry, Bangalore University, Bangalore, India.