Proton magnetic resonance study on solubilization by micellar alkylammonium propionates in carbon tetrachloride

Abstract

Solubilization of imidazole, methanol, 2-methyl-3-butyn-2-ol, iV-methylimidazole, and pyrazole by micellar butylammonium propionate (BAP), hexylammonium propionate (HAP), octylammonium propionate (OAP), and dodecylammonium propionate (DAP) in carbon tetrachloride was studied using proton magnetic resonance spectroscopy. Association constants (K) for the substrate-micelle complexes were calculated from chemical shift data. The association constants depend on the substrate structure and the number of carbon atoms (X) in the alkylammonium ion. For example, in case of association with DAP, imidazole binds more strongly than IV-methylimidazole (K = 65.3 ± 1.2, 28.8 ± 1.1 M-1, respectively) and 2-methyl-3-butyn-2-ol binds more strongly than methanol (K = 51.8 ± 4.0, 39.0 ± 3.4 M-1, respectively). For most of the solubilizates the association increases in going from BAP to OAP then decreases for DAP. For example, K for imidazole increases from 62.7 ± 1.8 to 105.8 ± 3.2 then decreases to 65.0 ± 1.2 M-1 and for IV-methylimidazole the corresponding K values increase from 32.2 ± 0.4 to 46.3 ± 3.0 then decrease to 28.8 ± 1.2 M-1, respectively.Catalysis by micellar systems has received much attention during the past few years.1-3 Micellar catalysis, both in water and in nonaqueous solvents, has been rationalized in terms of favorable substrate partitioning in the micellar pseudophase (or at its interface) where reactions take place. Data on the location and orientation of the substrates in the micelle and on the substrate-micelle association constants are, therefore, very important in understanding micellar catalysis. Solubilization by aqueous mi-