Decarboxylation of 6-Nitrobenzisoxazole-3-carboxylate Catalyzed by Ammonium Bilayer Membranes. A Comparison of the Catalytic Behavior of Micelles, Bilayer Membranes, and Other Aqueous Aggregates

Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate was studied at 5-50 °C in water in the presence of CTAB micelles, dialkylammonium (2CnN+2C1) bilayer membranes, and trioctylmethylammonium (TMAC) aggregates. These aqueous aggregates possess totally different morphologies with each other, but their general rate acceleration effects increased simply with increasing local hydrophobicities: CTAB < 2CnN+2C1 < TMAC. In contrast with the other systems, the rate enhancement by the dialkylammonium membrane was influenced by its hydrophobicity and fluidity. The crystal-to-liquid crystal phase transition determines the membrane fluidity. The Arrhenius plots for the membrane catalysis of 2CnN+2C1 (n = 12, 14, 16, 18) invariably showed inflections at or near the respective phase transition temperature (Tc). The activation energy data suggest that the membrane catalysis is governed mainly by the hydrophobicity and fluidity (or rather rigidity) at temperatures above and below Tc, respectively.