Reactions of B12r with Aliphatic Free Radicals: A Pulse-Radiolysis Study

Article abstract of DOI:10.1021/ja00379a014

The spectra of the intermediates formed in the reactions of B_12r with the free radicals Br2^-*, CO2^-*, *CH2C(CH3)2OH, *C(CH3)2OH, *CH2CHO, and *CH(OH)CH2OH are reported.The results indicate that Br2^-* oxidizes B_12r to B_12a, via an inner-sphere mechanism, and CO2^-* reduces B_12r to B_12s.All the aliphatic free radicals studied, *R, react with B_12r, yielding as the first product a pseudocoenzyme denoted Co^III-R.Co^III-CH2C(CH3)2OH is stable for over a second in the pH range 3-10 as is Co^III-CH2CHO.The latter compound hydrolyzes in acid solutions to yield B_12a and CH3CHO.Co^III-C(CH3)2OH and CO^III-CH(OH)CH2OH decompose heterolytically to yield mainly B_12s; a side reaction that probably yields Co^III-H via a β-hydride shift is also observed.The kinetics of decomposition of Co_III-CH(OH)CH2OH in neutral solutions are reported.No water elimination from the latter intermediate occurs.The reasons for the latter observation are discussed.