Surfactant effects on the reaction of 2-(4-cyano-phenoxy)-quinoxaline with hydroxide ion

A reaction of 2-(4-cyanophenoxy)quinoxaline 1 with hydroxide ion is accelerated by supramolecular aggregates of cetyltrialkylammonium chlorides (alkyl = Me, n-Pr, and n-Bu). in diluted surfactant solutions, with relatively high substrate concentration (7.0 x 10(-5) M), rate constants go through double rate maxima with increase in the surfactant concentration. The first rate maximum is ascribed to a reaction occurring in premicellar aggregates and the second to reaction in micelles. At low substrate concentration (7 x 10(-6) M), second-order rate constants in the micellar pseudophase are dependent on the surfactant headgroup size, which is related to charge dispersion in the transition state. Nonmicellizing tri-n-octylmethylammonium ions (TOAMs) increase the reaction of 1 with hydroxide ion. The observed rate enhancements may be due to the formation of small, hydrophobic aggregates which bind the substrate and promote the nucleophilic substitution reaction. (c) 2006 Wiley Periodicals, Inc.