Solvolysis of α-Bromo-p-aminostyrene. Mesomeric vinyl cations,Part IV

The preparation of α-bromo-p-aminostyrene ( 1b ) and its solvolysis rates and products have been reexamined in detail. In buffered 50 vol % aqueous dioxane between p_H* 13 and 3 the reaction rate is independent of hydrogen ion concentration. The ratio of the solvolysis products, viz. p-aminoacetophenone ( 3b ) and p-aminophenylacetylene ( 5a ), however, varies with the p_H* and with the buffer concentration. These findings confirm the unimolecular (S_N1-E1) mechanism involving an intermediate vinyl cation. The acid-catalysed hydration mechanism proposed by Schubert & Barfknecht is thereby excluded.