Comproportionation in propylene carbonate of substituted bipyridyliums. Rates and equilibria by rotating ring–disc electrode and associated electrochemical studies

Abstract

The comproportionation rate constants, k₁, and overall equilibrium constants, K_COMP, in propylene carbonate for a number of bis-N-substituted bipyridylium compounds ‘bipm^z+’(z= 2, 1, 0) have been measured, for bipm²⁺+ bipm⁰= 2 bipm^˙+ at 25 °C, by rotating ring–disc electrode studies and cyclic voltammetry, respectively. For like substituents the low slope (0.22) obtained from log k₁vs. log K_COMP deviates from the expected Marcusian value of ca. 0.5 as a consequence of the dimeric nature (bipm⁺)₂, of the immediate product. The rates and equilibria for this group satisfactorily follow the bond dipole moments of the substituents, except for the bis-p-aminophenyl substituent in which an exceptional intramolecular charge transfer interrupts the sequence.