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Kinetic study and analytical application of the hexadecyltrimethylammonium bromide-catalyzed reaction of 1-fluoro-2,4-dinitrobenzene with amines.

Arylation of amines by reaction with 1-fluoro-2,4-dinitrobenzene is catalyzed by micelles of cetrimonium bromide. This catalysis has been exploited to reduce the analysis time in the spectrophotometric determination of amines as their dinitrophenyl derivatives. The kinetics of the catalysis were studied for the five amines: alanine, phenylalanine, aniline, 4-methylaniline, and 4-methoxyaniline. The dependence of rate constant on surfactant concentration can be quantitatively accounted for by Berezin's model, in which uptake of the amine and the 1-fluoro-2,4-dinitrobenzene by the micelle is described as a partitioning phenomenon for both species. An alternative model is developed in which one reactant partitions into the micellar phase and the other binds to the micelle with 1:1 stoichiometry; the two models are formally equivalent. Intrinsic catalytic rate constants and binding constants were evaluated. About one-third to one-half of the maximum observed micellar acceleration is attributed to a true micellar catalysis, the remainder being ascribed to an increase in local reactant concentrations in the micelle.