Study of the derivatization of n-alkylamines with 1-fluoro-2,4-dinitrobenzene in the presence of aqueous cetyltrimethylammonium bromide micelles.

The use of aqueous cetyltrimethylammonium bromide micelles in the derivatization of n-alkylamines with 1-fluoro-2,4-dinitrobenzene was investigated systematically. The rate constants of derivatization of the n-alkylamines (C1-C8) were analysed using liquid chromatography. Up to butylamine the micellar rate enhancement depends on the electrostatic interactions between the amines and cetyltrimethylammonium bromide, and beyond C4 it depends mainly on the hydrophobic interactions. The reaction rates are also enhanced by a micelle-induced decrease of the pKa of the amines, but to a lesser extent. The derivatization rates for the longer alkylamines are comparable with those in dipolar aprotic solvents. Pharmaceutical and biomedical science is likely to benefit from the use of micellar systems in pre-column derivatization reactions in aqueous solutions.