Kinetics and Mechanism of Oxidation of Some Diols by Dihydroxydiperiodatoargentate(III) in Alkaline Medium

Abstract

The kinetics of oxidation of ethylene glycol and 1,3-butylene glycol by dihydroxydiperiodatoargentate(III) in alkaline medium have been studied by spectrophotometry in the range of 298.2-318.2 K. It is shown that the reaction was first order with respect to each reductant and Ag(III), and k obs increased with an increase of [OH -]. A plausible mechanism of reaction involving a pre-equilibrium of adduct formation between complex and reductants was proposed, which could be applied to explain all experimental phenomena, and the activation parameters of the ratedetermining step have been also calculated.

Do oxidations of α-diols by bis(hydrogenperiodato)argentate(III) proceed according to different rate laws?

“…2. The different rate laws reported previously in the literature [4,5] are probably incorrect; in turn, the mechanisms proposed from these rate laws should be considered with due caution.…”

“…2 (solid curve). It appears that the rate law established from a narrow range of [Ethylene Glycol] in [4] is not sufficient when the concentration range is extended.…”

“…Since our reaction conditions were somewhat different from those used by Shan et al, it was necessary to repeat the kinetic measurements under identical conditions to those used in [4] but with a wider range of [Ethylene Glycol]. Under such conditions, k obs as a function of [Ethylene Glycol] is also displayed in Fig.…”

“…In [4], it was reported that the reaction between [Ag(HIO 6 ) 2 ] 5-and ethylene glycol was first-order in ethylene glycol as a plot of k obs versus [Ethylene Glycol] was linear and passed through the origin. Since our reaction conditions were somewhat different from those used by Shan et al, it was necessary to repeat the kinetic measurements under identical conditions to those used in [4] but with a wider range of [Ethylene Glycol].…”

“…Shan and coworkers have recently reported kinetic studies on the oxidations of ethylene glycol [4] and 1,2-butanediol [5] by the Ag(III) complex. However, the reported rate laws and the proposed mechanisms were markedly different in these two studies.…”