Kinetics of Alcohol Oxidation by Electrochemically Generated Superoxide Ions in Ionic Liquids Using Double Potential Step Chronoamperometry

Double Potential Step Chronoamperometry (DPSC) was used to determine the rate constants for the homogeneous reactions of alcohols with the superoxide ion (O2 ?-) at different temperatures in two room temperature ionic liquids (RTILs). The technique was first tested by determining the pseudo first order rate constant for reduction of azobenzene to hydroazobenzene that, in turn, undergoes the benzidine rearrangement. Our results were in good agreement with values reported in the literature using DPSC and conventional kinetic methods. The activation energy for the oxidation of benzyl alcohol is 19.1 kJ/mol in [bmim][HFP]; which is in good agreement with the value reported in the literature. The corresponding values of S? ? , H? ? and G? ? for the reaction of superoxide ion with benzhydrol in [bdmim][HFP] calculated at T=45?C are –0.49 kJ/mole, 22.4 kJ/mole, and 177.9 kJ/mole, respectively. The second order rate constant for the oxidation of benzyl alcohol at 10?C in RTIL in [bmim][HFP] was determined to be ?1.3 L mol-1 s-1. The pseudo first order rate constant for the homogeneous reaction of O2 ?- with different primary andsecondary alcohols in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][HFP]) and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [bdmim][HFP] at different temperatures was measured. The pseudo first order rate constant for the reaction of O2?- with benzhydrol in [bdmim][HFP] at T= 49, 57, 65, 84 C were found to be 60, 72, 92, 148 L mol-1 s-1. The pseudo first order rate constant for the reaction of O2?- with benzhydrol in [bmim][HFP] at T=27, 40 and 80 ?C were found to be 53,74, 201 L mol-1 s-1.The Arrhenius plot was then used to determine the activation energy and pre-exponential factor for the corresponding reactions