Nucleophilic Addition to Olefins. 2. Reaction of Benzylidene Meldrum's Acid with Water, Hydroxide Ion, and Aryloxide Ions. Complete Kinetic Analysis of the Hydrolytic Cleavage of the C=C Double Bond

Article abstract of DOI:10.1021/ja00524a022

The kinetics of reversible nucleophilic attack by water, hydroxide ion, phenoxide ion, and p-bromophenoxide ion on benzylidene Meldrum's acid was measured in aqueous solution by the stopped-flow method.The rate of protonation on carbon of the anionic addition complex between benzylidene Meldrum's acid and hydroxide ion was also measured.The combination of our results with literature data on the rate of hydrolytic cleavage of benzylidene Meldrum's acid allowed us to map out a detailed mechanism of the cleavage reaction and assign rate-limiting step in different pH ranges.At high pH, protonation on carbon of the anionic addition complex is rate limiting; at low pH, deprotonation of the OH group in the neutral addition complex is rate limiting, which implies a rate constant for the breakdown of the tetrahedral intermediate by carbanion departure on the order of, and probably exceeding, 10¹⁰ s^-1.