Kinetics and mechanism of the nucleophilic substitution of arylhalogenoacetylenes by sodium toluene-p-thiolate in NN-dimethylformamide
Abstract
The title reaction of 1-chloro- and 1-bromo-2-phenylacetylenes and of their p-Me and p-Cl substituted derivatives has been kinetically studied. Only 1-p-tolylthio-2-arylacetylenes are obtained, provided an excess of thiolate is avoided. By use of excess of thiolate, an addition reaction takes place on the substitution product. Ratios kRCl:kRBr in the range 2·5–4·2 have been found for the substitution at –25°C. Hammett ρ values of 3·4 and 3·9 are calculated for chloro- and bromo-acetylenes, respectively. In agreement with these results, p-NO2·C6H4·C![[triple bond, length half m-dash]](https://www.rsc.org/images/entities/char_e007.gif)
CBr gives a fast substitution even at –50 °C. Results are interpreted on the basis of the α-addition–elimination mechanism for substitution at an acetylenic carbon atom.
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