ELECTROCHEMICAL REDUCTION AND INTRA-MOLECULAR CYCLIZATION OF 6-IODO-1-PHENYL-1-HEXYNE AND 6-BROMO-1-PHENYL-1-HEXYNE AT MERCURY CATHODES IN DIMETHYLFORMAMIDE

Polarograms for 6-iodo-1-phenyl-1-hexyne and 6-bromo-1-phenyl-1-hexyne in dimethylformamide containing tetra-n-butylammonium perchlorate exhibit three waves, the first being due to reduction of the carbon-halogen bond. Superimposed upon the first wave for each compound is a large current maximum which is concentration dependent and much more pronounced for the iodo species. Large-scale electrolyses were carried out at potentials corresponding to the first wave to avoid reduction of the carbon-carbon triple bond and subsequent isomerization of the alkynes to their respective allenes; coulometric n values were found to be unity. At potentials on or before the polarographic maximum, controlled-potential electrolyses yield large quantities of diorganomercury compounds (containing both alicyclic and acyclic organic moieties) which indicate direct involvement of the mercury cathode in the reduction process. A variety of straight-chain and alicyclic monomers, derived from both radicals and carbanions, are included among the products, and the amounts of these species vary systematically with potential and the initial concentration of starting material. In addition, minor quantities of an alcohol and N-methylformamide adduct formed from the acetylenic halides are observed; these products arise by reaction of hydroxide ion with unreduced parent compound. © 1979, American Chemical Society. All rights reserved.