Kinetics And Mechanism Of Oxidation Of Dihydric Alcohols And Alcohol-amines By Ni(IV) Ion Spectrophotometrically

The studies of oxidation of some simple organic compounds by Ni(IV) complex in previous works, which applied inprotonated complex [Ni(OH)2(H3IO6)2]2- as existed form to undergo electron transfer reaction.The kinetics and mechanism of oxidations of dihydric alcohols with a ?y-active group and a series of alcohol-amines by dihydroxydiperiodatonickelate(IV) in alkaline medium by the method of spectrophotometry were investigated. We also studied the influence of OH" on the constant of rate. If the deprotonated complex [Ni(OH)2(HIO6)]2- was presumed as the active species, the plot of l/kobs vs f([OH"])/[OH~] should be linear, which was in accordance with our experimental results. However, if the inprotonated complex [Ni(OH)2(H3lO6)2]2- was presumed as existed form, the plot of llkobs vs F([OH"])/[OH-] was a curve, which was not consistent with our experimental results.Based on calculated and experimental results, we proposed that the mechanism should be that the deprotonated complex was the active species, forming the intermediate adduct with the reductant and completing the reaction through electron transfer. Based on the studies of dihydric alcohols, we know that the reaction rate of the determining-step changed with the changing of the position of the oxidized group. The reaction rate of the determining-step have such a sequence: a -Propylene glycol>?Butylene-glycol >y-Butylene-glycol. Comparing dihydric alcohols with alcohol-amines, we find that the reaction rate of the determining-step changed with the changing of the oxidized group, namely, the rate of -NH3 is larger than that of -ROH. Comparing to previous work, we have a conclusion that the reaction rate changed with active-group, the observed rate constants of the rate-determining step of diethanolamine are larger than tetrahydrofurfuryl alcohol.The supposed mechanism could favorably explain the reaction results. Meanwhile, the rate constants (K) and activation parameters were obtained at different temperatures.The hypothesis that the complex was existed as the deprotonated form was supported by our experimental results. Our studies on this kind of system will provide us with more dynamical parameters, and provide theoretical foundation for the route design of the organic synthesis and quantitative analysis of analytical chemistry.