SPECIFIC MICELLAR RATE EFFECTS ON UNIMOLECULAR DECARBOXYLATION AND CYCLIZATION

Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion and cyclization of omicron-3-halopropyloxyphenoxide ion (PhY7; Y = Br, I) are accelerated by aqueous cationic and zwitterionic micelles. For cationic micelles the rate enhancements (k'M/k'W) increase with increasing bulk of the surfactant head groups but are largest for decarboxylation. There are good linear free energy relationships between micellar effects on these reactions and the plots of log k'M for cyclization against log k'M for decarboxylation have slopes of 0.46 and 0.64 for Y = Br and I, respectively. Surfactants that have twin tail or tri-N-alkylbenzyloxy head groups do not fit the relationship. Despite mechanistic differences between decarboxylation and cyclization (an intramolecular S(N)2 reaction), similar factor control micellar effects on these reactions. In the absence of surfactant there is only a qualitative relationship between free energies of activation of cyclization and decarboxylation in different solvents.