OXIDATION OF 10-METHYLACRIDAN, A SYNTHETIC ANALOG OF NADH, AND DEPROTONATION OF ITS CATION RADICAL - CONVERGENT APPLICATION OF LASER FLASH-PHOTOLYSIS AND DIRECT AND REDOX CATALYZED ELECTROCHEMISTRY TO THE KINETICS OF DEPROTONATION OF THE CATION RADICAL

Photolysis of 10-methylacridan (AH) in acetonitrile solutions containing CCl4 led to quantitative oxidation of AH to A+. Laser flash photolysis of the solution with 248- or 308-nm light yielded the cation radical AH.+ which decays by deprotonation to give the neutral radical A.. AH.+ could be also generated by means of homogeneous redox catalysis using variously substituted ferrocenes and the rate of deprotonation k(H) by various bases was derived from both techniques. There is a good agreement between the values determined for k(H) (here and, previously, by direct electrochemistry using ultramicroelectrodes). The vast majority of the data points in a plot of log k(H) vs the pK(a) of the bases, covering 18 pK(a) units and rate constants up to the diffusion limit, fall on the same Bronsted line in spite of the fact that they involve bases of quite different structure: pyridines, aliphatic nitrogen bases, and carboxylates. Gamma-radiolysis of acetonitrile/CCl4/AH solutions also resulted in quantitative oxidation to A+. However, pulse radiolysis of this system indicated relatively slow oxidation of AH by Cl3COO. radicals. Pulse radiolysis experiments in acidic aqueous solutions showed that AH is oxidized by Cl2.- to give AH.+, which decays with a first-order rate constant of 9 x 10(2) s-1. Reduction of A+ gave A. which did not undergo protonation even at 2 M HClO4, but reaction of A+ with H atoms resulted in partial addition of H to the 9-position to give AH.+.