Abstract
The dissociation constants (Ka) of the conjugate acids of the p-dimethylaminobenzylidene derivatives (I) of various active methylene compounds (XYCH2) were determined. Alkaline hydrolysis of I was studied kinetically in 30% (v/v) ethanol at 25°C. The rates of nucleophilic attack of a hydroxide ion on the carbon-carbon double bonds of I were linearly correlated with the corresponding pKa values. Thus the pKa values are suggested to be useful parameters to evaluate the relative activating ability of the X and Y groups to support the attack of nucleophiles on compounds of the type XYC=CHAr. In the hydrolysis of structurally similar compounds α-(substituted benzoyl)-p-dimethyl-aminocinnamonitriles, the rates of carbon-carbon bond fission of an uncharged addition intermediate and those of carbon-carbon double bond formation from a carbanion intermediate were also correlated with the dissociation constants (KAMa) of the corresponding substituted benzoylacetonitriles. The pH-rate profile and the relationship between rates and Ka (or KAMa) suggested that the carbon-carbon bond fission of the uncharged intermediate is the rate-determining step in the alkaline hydrolysis of I.
