Stereochemistry of the Cathodic Reduction of Halogenated Organic Derivatives

Investigations on the stereochemistry of the electrochemical reduction of organic halogeno-derivatives are reviewed, and a comparison is made of the behaviour of these compounds on mercury and on platinum. Specific interaction between the halogen and the mercury electrode is shown to occur during reduction: i.e. direct contact between the halogeno-derivative and mercury is a condition for production of the transition state. In the reduction of optically active halogenocyclopropanes electron transfer occurs from the halogen atom with formation of a carbanion having the same configuration as the original halogeno-compound, but subsequent reactions (protonation, inversion, sp³–sp² transition, etc.) may have a substantial effect on the configuration of the final product. The simultaneous detachment of two halide anions in the reduction of vicinal dihalogeno-derivatives results in the formation of compounds containing multiple bonds.
A list of 40 references is included.