Micellar catalysed elimination reactions of p-substituted phenethyl bromides and related compounds in alkaline solutions
Abstract
The rates of dehydrobromination of para-substituted β-phenethyl bromides (3) were determined in alkaline solutions under micellar (kψ) and non-micellar (k0) conditions by using hexadecyltrimethylammonium bromide (1) and di-methyl-(2-hydroxyethyl)octadecylammonium chloride (2) as the micellar surfactants. Large micellar effects (kψ/k0) were observed. Good Hammett relationships were obtained for both kψ and k0 with σp– constants. Fairly large isotope effects (kH/kD= 8–9) were also observed for both kψ and k0. The results suggest that the transition states are more carbanion-like under the micellar conditions compared with the non-micellar conditions. However, H–D exchange of the starting bromides with solvent water, which would indicate carbanion formation prior to elimination, was not detected.