THERMODYNAMICS OF SEMIQUINONE DISPROPORTIONATION IN AQUEOUS BUFFER

The thermodynamic parameters, K-disp, Delta H degrees and Delta S degr ees, controlling the disproportionation of semiquinones derived from 1 ,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 2-methylbenzoquinone (M BQ), menadione (MNQ), naphthazarin (NZQ) and quinizarin (QNZ), have be en determined. Smaller disproportionation constants, K-disp, are obser ved upon addition of a fused benzene ring to the semiquinone structure . Negative enthalpies and positive entropies of disproportionation gov ern the disproportionation equilibria. Addition of OH groups to the 5 and 8 positions in NQ(.-) displaces the disproportionation equilibrium to the semiquinone probably due to intramolecular hydrogen bonding.