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, KCOMP, in propylene carbonate for a number of bis-N-substituted bipyridylium compounds ‘bipmz+’(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 KCOMP 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.