Nucleophilic attack on halogeno(phenyl)acetylenes by halide ions
Abstract
Nucleophilic reactions between halogeno(phenyl)acetylenes and halide ions, ArCCX + Y–, where Ar = C6H5 or p-ClC6H4, X = Cl or Br, and Y = Cl or Br, have been examined. Halogen exchange of the Finkelstein type was observed for the first time in acetylene halides in anhydrous dimethyl sulphoxide when X = Br and Y = Cl. This exchange did not occur with other X–Y combinations. In the presence of up to 20% water in dimethyl sulphoxide, or under aqueous–organic phase-transfer catalytic conditions, nucleophilic addition (formally of HY) took place for all the X–Y combinations studied. In the additions, the nucleophile Y– invariably attacked the carbon to which the phenyl group was bound. The mode of HY addition was stereospecifically trans; accordingly, the resulting dihalogenostyrenes always had the (Z)-1,2-dihalogeno-configuration.