G. D. Allen, Marisa C. Buzzeo, Constanza Villagrán
Feb 1, 2005
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Journal
Journal of Electroanalytical Chemistry
Abstract
Abstract The oxidation of bromide has been investigated by linear sweep and cyclic voltammetry at platinum electrodes in the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, ([C 4 mim][NTf 2 ]), and the conventional aprotic solvent, acetonitrile, (MeCN). Similar voltammetry was observed in both solvents, despite their viscosities differing by more than an order of magnitude. DigiSim ® was employed to simulate the voltammetric response. The mechanism is believed to involve the direct oxidation of bromide to bromine in a heterogeneous step, followed by a homogenous reaction to form the tribromide anion: 2 Br - → Br 2 + 2 e - Br 2 + Br - ⇌ k b k f Br 3 - K eq Athigher potentials, the tribromide anion dissociates to bromine, Br 2 , and bromide, Br − , which is immediately oxidised, leading to the emergence of a second anodic wave. Irreversible electrode kinetics were inferred from Tafel analysis and removal of the first electron is believed to be the rate-determining step in the formation of bromine. The equilibrium constant, K eq , where K eq = [ Br 3 - ] [ Br 2 ] [ Br - ] was found to be 3 × 10 3 and 9 × 10 6 M −1 in the ionic liquid and in acetonitrile, respectively. An equilibrium constant, K complex for the complexation of 1-ethyl-3-methylimidazolium bromide in acetonitrile was found to be 35.1 M −1 .