The reduction of xanthylium cation by BNAH has been thoroughly investigated. The observed kinetic isotope effect, radical inhibitor (DNB) effect, and the driving forces for each mechanistic step in various mechanisms indicate that the reaction proceeds via an initial rate-determining electron transfer and is followed by a fast hydrogen atom abstraction. The kinetic activation parameters measured in this work show that there is a preequilibrium between two reactants prior to the electron transfer. The mechanisms of the reductions of 9-phenylxanthylium and triphenylmethylium cations by BNAH are also discussed.

Key words: DYNAMICS, REACTION MECHANISM, THERMODYNAMICS, REDUCTION REACTION, ISOTOPE EFFECT, INHIBITOR, TRIPHENYLMETHANE, COENZYME, CARBONIUM, ELECTRON TRANSFER REACTION