Hydrolysis of Electrophilic Olefins. II. Kinetic Studies on the Hydrolysis of m- or p-Substituted α-Benzoylcinnamonitriles

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The hydrolysis of m- or p-substituted α-benzoylcinnamonitriles (I) was studied kinetically in 30% (v/v) ethanol (pH 2-13) at 25°C. The pH-rate profile showed a maximum at nearly neutral pH and an inflection point at weakly acidic pH. The pH-rate profile and substituent effect suggested that the rate-determining step is the carbon-carbon bond fission of an addition intermediate in the strongly acidic range, and is the nucleophilic attack of water on the carbon-carbon double bond of I in the weakly acidic range. It was also suggested that the hydrolysis of I, except for the compounds with strongly electron-withdrawing substituents, CN and NO₂, involves appreciable carbon-carbon bond fission of the addition intermediate at the transition state of breakdown of the intermediate on the basis of the large negative ρ values observed in the alkaline range. Deviation in the cases of the above substituents from the Hammett plots and the enthalpy-entropy relationships appears to show that in these compounds the processes of carbon-carbon bond fission are concerted with deprotonation of the alcoholic hydroxy group of the intermediate.