Nucleophilic displacements at halogen in 1‐chloro‐, 1‐bromo‐ and 1‐iodo‐1‐alkynes: I. Thiolates as nucleophiles

Abstract

Abstract Second‐order rate constants, k 2 , of reactions of thiolates with several 1‐aryl‐2‐halogenoacetylenes and 1‐halogeno‐2‐(2‐thienyl)acetylenes were measured in methanol‐water mixtures. For meta ‐ and para ‐substituted 1‐bromo‐2‐phenyl acetylenes these rate constants correlate well with Hammett σ constants: p 1.15. Linear correlations were observed between log k 2 and p K a of the corresponding thiols. The nucleophilicity constants, n , for substitution on bromine and iodine appear to be quite different from those for substitution on other atoms like carbon, sulfur and platinum. It was possible to correlate all the rate constant with E and H in the oxibase scale of Edwards.