In situ electrochemical electron spin resonance. The catalytic (EC′) mechanism

Abstract

The oxidation of the acetate anion mediated by tris(4-bromophenyl)ammoniumyl, electrogenerated from the parent amine, has been investigated using ESR with an in situ channel electrode flow cell. In the absence of acetate, the oxidation of tris(4-bromophenyl)amine (TBA) is a reversible one-electron process which forms the corresponding radical cation, tris(4-bromophenyl)ammoniumyl (TBA^˙+). In the presence of acetate the process takes on the characteristics of the catalytic (EC′) mechanism. Analysis of the diffusion-limited current/electrolyte flow rate and ESR signal/current/electrolyte flow rate behaviour allows the precise mechanism to be deduced. This is shown to be an EC′ pre-equilibrium mechanism: TBA – e → TBA^˙+, TBA^˙++ CH₃CO^–₂⇌ TBA + CH₃CO^˙₂, CH₃CO^˙₂→ CH^˙₃+ CO₂ with rate-determining electron transfer between the amine radical cation and the acetate anion.