Proton-Electron Transfer: Kinetics and Mechanism in the Ketone-Ketyl Redox System

Article abstract of DOI:10.1021/j100334a020

Rate constants for the two ketyl-ketone redox systems AH^. + K -> A + KH^. (7) and K^*H^. + K -> K^* + KH^. (14), where AH^., K^*H^., KH^., K, and A are dimethylketyl (Me2C^.OH), 4-tert-butyldiphenylketyl, diphenylketyl (Ph2C^.OH), benzophenone, and acetone, are k₇ = (3.5 +/- 1.5) * 10⁴ M^-1 s^-1 and k₁₄ = (1.5 +/- 0.2) * 10⁴ M^-1 s^-1* at 298 K.The value for k₇ is significantly lower than previous literature reports for this number.However, the current values for both k₇ and k₁₄ are consistent with considerable chemical evidence from other sources.It is shown that these reactions, although formally hydrogen transfers, cannot occur by a "normal" H atom transfer.They also do not occur by sequential transfer of a proton followed by an electron, or vice versa.Instead it is proposed that the carbonyl acts as a dual-site receptor for proton and electron transfer from the dual-site donor, the reducing ketyl radical.