Electrochemical Reduction of 1-Iodo-5-decyne and 1-Bromo-5-decyne at Mercury Cathodes in Dimethylformamide

Article abstract of DOI:10.1021/jo00167a025

Pulse polarograms for 1-iodo-5-decyne in dimethylformamide containing tetramethylammonium perchlorate exhibit two waves.At potentials corresponding to the first wave, electrolysis of 1-iodo-5-decyne at mercury results in 5-decynyl radicals that (i) adsorb onto and interact with the mercury electrode to give 5-decynylmercury radicals which disproportionate into di-5-decynylmercury or (ii) cyclize and then accept a hydrogen atom to yield pentylidenecyclopentane.At potentials on the second wave, reduction of 1-iodo-5-decyne is largely a two-electron process leading to the 5-decynyl carbanion which is protonated by water in the solvent-supporting electrolyte to yield 5-decyne and hydroxide ion; hydroxide ion then attacks unreduced starting material to give 1-decen-5-yne and 5-decyn-1-ol.In the presence of excess proton donor (diethyl malonate), neither 1-decen-5-yne nor 5-decyn-1-ol is obtained, but diethyl 5-decynylmalonate is produced, the quantity of 5-decyne is increased, and the coulometric n value is raised.Pulse polarograms for 1-bromo-5-decyne show a single wave.For reduction of 1-bromo-5-decyne, the yields of 5-decyne and 1-decen-5-yne are comparable to those derived from 1-iodo-5-decyne; some di-5-decynylmercury is produced, but no pentylidenecyclopentane is formed.