Effect of Chain Branching on Electrochemical Carbon-Halogen Bond Fission. Possible Mechanism for the Process

Abstract

As part of a continuing study of the electrochemical reduction of carbon‐halogen bonds, a group of branched‐chain α‐bromoalkanoic acids with several of their ethyl esters and straight‐chain isomers were investigated polarographically. The relation between half‐wave potential, , and pH for the acids follows an S‐shaped pattern having pH‐invariant regions in the alkaline and acidic ranges, in the latter region being considerably more negative. The values for the esters are pH‐independent, being slightly more positive than those of the corresponding acids in the acidic region. Polarographic waves all involve a diffusion‐controlled two‐electron reduction. In the acidic region, the branched‐chain acids are more easily reducible than their straight‐chain isomers by 0.20 to 0.13 volt, the larger differences being observed for the lower molecular weight acids. In the alkaline region the situation is more complicated; all acids in the series having ethyl groups or larger in the α‐position have their shifted to more negative values.