Micellar Catalysis of Organic Reactions. 27. Micellar Bound Meisenheimer Complexes

Article abstract of DOI:10.1021/jo00299a035

Reactions of nitro activated aryl halides with base in the presence of dihydroxy micelles of cetyl(2,3-dihydroxypropyl)dimethylammonium bromide (CDHPDAB) give rise to spiro Meisenheimer complexes that are covalently bound to the micelles.From the large fluorine/chlorine rate ratios observed for these reactions, we conclude that the initial attack on the aryl halide by the micellar hydroxyl group is the rate-determining step for the formation of the Meisenheimer complex.For the subsequent decomposition of the complex the rate of reaction is dependent on hydroxide concentration if the complex contains only one ortho substituent.This indicates that the breakdown of the aryl micellar ether formed in the first step of the decomposition is the rate-determining step.However, for complexes containing two ortho substituents, the rate of decomposition is almost independent of the hydroxide concentration, indicating for these complexes that the rate-determining step is the initial unimolecular breakdown of the Meisenheimer complex to form the micellar ether.It is proposed that this change is caused by the built-in solvation effect of Bunnett et al. in which the positive charge on the side chain of the complex is stabilized by an electrostatic interaction with either the negatively charged carboxylate group or the dipolar nitro group.