Hydrogen isotope effects in electrochemical reductions of organic chloro compounds

The kinetic hydrogen isotope effects in electrochemical reductions of CCl3C OOD, CDCl2COOD, CCl4, CDCl3, benzyl chloride, 1-chloronaphthalene and 4-chl orobenzo-nitrile in deuterated reaction media were determined. The aliphati c chloro compounds are reduced with rather small isotope effects k(H)/k(D) = 1.2...1.7, as expected if anionic intermediates are formed and protonated . Benzyl chloride is reduced with an apparent k(H)/k(D) = 2.1, which is pro bably too high due to radical reactions. Aromatic chloro compounds are redu ced with significant participation of a second mechanism via radical interm ediates which abstract carbon-bound hydrogen atoms from the components of t he reaction system. The resulting isotope effects are k(H)/k(D) = 1.2 for t he part of the reduction which proceeds via anions and k(H)/k(D) similar to 2.5 for the competing radical reaction.