The chemistry of vitamin B12. Part VIII. Controlled potential reduction of vitamin B12a

Abstract

Controlled potential coulometric analysis has been used to measure the number of electrons involved in the reduction of some vitamin B₁₂ compounds. The reductions of B_12a to B_12r, and B_12r to B_12s, each require one electron. Analyses of the numbers of protons involved in the reactions show that B_12s is not a hydride. The rate constants for the reductions are analysed in detail since a catalytic current is observed in the case of reduction to B_12s. The rate constant for the decomposition of B_12s in the absence of oxygen has been determined from these data and agrees with that determined by a polarographic method. The rate of decomposition depends on the pH of the solution and on the buffer anions present. It is suggested that B_12s can catalyse the reduction of some anions or of water.