DIPOLAR MICELLES .8. HYDROLYSIS OF SUBSTITUTED PHENYL ESTERS IN A HYDROXAMIC ACID SURFACTANT

The reactions of hydroxamic acid catalysts of the structure [formula omitted] with substituted phenyl esters have been studied. The kinetics in I3C followed the expression: [Formula Omitted]. The water catalysis rates ko for all the esters studied were significantly greater than the spontaneous rate constants reported in the literature for esters of identical leaving groups. The magnitude of the water rate constants, and their dependence on microenvironmental factors as displayed by mixed micellar systems, indicated that the reaction proceeds via electrophilic assistance by the onium head groups. Nucleophilic attack by the hydroxamate anion (kc) in I3C on the esters corresponds to a β Brönsted value of -1.1. The results point out that although I3C is expected to be an α-effector catalyst, the relative enhancement of the rate constants is very small. This was explained in terms of proximity and electrostatic effects in the transition state. The basic hydrolytic rates koH and the titrimetric behavior of I3C were also discussed. © 1979, American Chemical Society. All rights reserved.