Hydrogen Isotope Effects in Electrochemical Reductions of Organic Chloro Compounds

Abstract

The kinetic hydrogen isotope effects in electrochemical reductions of CCl,COOD, CDClzCOOD, CCb, CDCl2, benzyl chloride, lchloronaphthalene and Cchlorobenzonitrile in deuterated reaction media were determined. The aliphatic chloro compounds are reduced with rather small isotope effects kH/kD = 1.2.. . 1.7, as expected if anionic intermediates are formed and protonated. Benzyl chloride is reduced with an apparent kH/kD = 2.1, which is probably too high due to radical reactions. Aromatic chloro compounds are reduced with significant participation of a second mechanism via radical intermediates which abstract carbon-bound hydrogen atoms from the components of the reaction system. The resulting isotope effects are kH/kD = 1.2 for the part of the reduction which proceeds via anions and kH/kD -2.5 for the competing radical reaction.

Current electrochemical approaches to selective deuteration

“…A similar methodology was used in the same decade for pseudohalides 42 and certain alkyl halides. 43 In more recent years, Suga demonstrated the use of a fluorenone redox mediator for the reductive deuteration of aryl halides. 44 In this case, deuterium was delivered from d 3 -MeCN, however with some methylation by-products.…”