Addition of sulphenyl chlorides to acetylenes. Part VIII. Effect of acids on the orientation

The orientation of the addition of benzenesulphenyl chlorides to phenylacetylene in ethyl acetate is largely shifted from anti-Markownikoff to Markownikoff by strong acids like trifluoroacetic and hydrochloric. No effect was observed on the addition to but-1-yne. The results fit the scheme proposed to explain the effect of solvent on the orientation, and confirm that production of the Markownikoff orientation is related to the possibility of forming a highly polar structure from an initial adduct between the sulphenyl chloride and the aceylene derivative, which would otherwise yield the anti-Markownikoff adduct by internal collapse. A further proof of the trans-stereochemistry of the additions is given.