Mechanistic study of osmium(VIII) promoted oxidation of crotonic acid by aqueous alkaline solution of potassium iodate

Kinetics and mechanism of Os(VIII) promoted oxidation of crotonic acid (CA) by alkaline solution of potassium iodate (KIO3) have been investigated at 35 degrees C. Zero order kinetics with respect to potassium iodate is observed. The reaction exhibits, linear dependence of reaction fate at low [CA], tending towards zero order at its higher concentrations. First order kinetics with respect to catalyst osmium tetroxide (OsO4) has been observed. Accelerating effect of [OH-] ion on reaction rate is also observed. The reaction shows negligible effect of variation of ionic strength of the medium, while a marked effect of rise in temperature on the rate is observed. IO3- and [OsO4(OH)(2)](-2) are postulated as the reactive species of potassium iodate and Os(VIII), respectively. The reaction has been studied at four different temperatures (30, 35, 40 and 45 degrees C) and the overall activation parameters have been computed. A plausible mechanism conforming to the observed kinetics has been suggested. The main oxidation products have been identified as acetic acid and glyoxylic acid. A suitable mechanism involving attack of potassium iodate species on complex formed between catalytic species of osmium tetroxide and crotonic acid in the slow and rate determining step is suggested. The rate law, Rate = -d[KIO3]/dt = kd K1K2[CA] [OH-][Os(VIII)(T)/1+K1K2[CA][OH-] is consistent with observed kinetic results.