Hydrolysis of α-cyanobenzylideneanilines. Part I. Kinetic studies in acidic media

Abstract

The hydrolysis of α-cyanobenzylideneanilines was studied kinetically in aqueous sulphuric acid (H₀–2 to –6), 40% aqueous acetonitrile (pH 3–0), and 60% aqueous dioxan (H₀ 1·5 to –2) at 25°. Benzoyl cyanide was demonstrated to be an intermediate. The rate of hydrolysis exhibited a maximum at H₀ca.–1 to –2. The effect of substituents on the reaction rate and the Bunnett–Olsen ϕ values suggested that the hydration of the protonated substrate is rate determining on the less acidic side of the rate maximum and that the decomposition of the intermediate amino-alcohol is rate determining under more acidic conditions. It is suggested, from consideration of the shape of the acidity–rate profile, that aniline is expelled only from the dipolar form (or zwitterionic form) of the amino-alcohol intermediate, because the tendency for aniline to separate is weakened by the electronwithdrawing cyano-group.