Modification of the order of reaction and reaction rate of nucleophilic aromatic substitution in micellar solutions

Abstract

The rate of formation of 2,4,6-trinitrodiphenylamine following the attack of aniline on 1-methoxy-2,4,6-trinitrobenzene has been studied in micellar media. The partial order with reference to the nucleophilic reagent (aniline) is unity in solutions of cationic detergents (positive micelles) and 3/2 in water or solutions of anionic detergents. For such reactions there are two main steps in the reaction scheme: first, the formation of an adduct between reagents, favoured by the effect of local higher concentration in the two kinds of micellar solutions and secondly, ejection of a proton from the adduct formed. The latter reaction is catalysed largely by positive micelles and in this case the kinetics are not limited by the deprotonation step. On the other hand, negative micelles inhibit the ejection of a proton and this opposes, in part, the effect of higher local concentrations.