Logarithms Of Second-order Rate Constants Research Articles

Hydrolysis of α-cyanobenzylideneanilines. Part 2. Kinetic studies in basic media

The base-catalysed hydrolysis of α-cyanobenzylideneanilines (I) was studied in aqueous dioxan (40 and 50% v/v) at 30°C. The rate of hydrolysis was first-order with respect to hydroxide ion. The plot of the logarithm of second-order rate constants for (I) with substituents on the C-phenyl ring against the σ value was linear (ρ 2.10), whereas that for (I) with substituents on the N-phenyl ring was concave. These results were compared with those for the reaction of (I) with ethoxide ion, where similar substituent effects were observed. These results were interpreted in terms of a mechanism involving tetrahedral addition intermediate, where the attack of hydroxide ion on the substrate is probably rate-determining. The curved Hammett plot cannot be ascribed to a change in mechanism, but seems to result from some other factors.