Chemical Reactivity and Basicity of Amines Modulated by Micellar Solutions

Abstract

The kinetics of the reactions of several secondary aliphatic amines with alkyl nitrites (2-bromoethyl and 1-phenylethyl nitrites) weee measured using the spectrophotometric technique in aqueous basic solutions and in the presence of sodium dodecyl sulfate and tetradecyltrimethylarnmonium bromide. In the case of the cationic micelles, the results were quantitatively interpreted by means of the pseudophase model, which considers micelles acting as a separate phase from water. With the anionic micelles, the results weee analyzed by using the simple pseudophase ion-exchange model, in which the alkyl nitrite and the neutral form of the amine are partitioned between the micellar and aqueous pseudophases, and in which the basic ionization equilibria of the amine increases because of the exchange between the alkylammonium ion of the amine and the micellar counterion at the micellar surface. Bimolecular rate constants for the reaction in the micellar pseudophase are always smaller than for those in water. Characteristic features of the media and of the substrates in the reactivity behavior of amines are discussed. The binding constants of the amines (by hydrophobic or electrostatic effects) to the micelle are seen as related to the structure of the amine and the nature of the micellar surface. © 1995, American Chemical Society. All rights reserved.