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The rates of formation and dissociation of the thermoadditioncomplex of 1,3,5-trinitrobenzene with OH-has been investigated in micellar solutions of dodecyltrimethylammonium bromide (DTABr) using a stopped-flow spectrometer. We have observed and measured three processes which proceed under different conditions of acidity: (a) formation of the r~ complex, (b) spontaneous (equilibrium) dissociation in less basic solutions and (c) dissociation via proton attack in acid solutions. These processes are influenced by the background KBr electrolyte. The interphase potential A$ = drn -&, depicted in the pseudophase model, allows us to explain the variations of the rate constants.The catalytic effect of cationic detergents, for example dodecyltrimethylammonium bromide solutions with water (DTABr), on nucleophilic aromatic substitution reactions has been studied by several workers.l-13 1 -Halogeno-2,4-dinitrobenzene compounds have often been used and reacted with the hydroxide ion, OH-, to form the corresponding phenate; the catalytic effect on such reactions is significant. In contrast, few investigations14-16 have been made on aromatic substitutions in which 0 addition complexes (or Meisenheimer complexes) are formed, e.g. when the aromatic substrate is a trinitrosubstituted benzene compound. The aim of this work is to investigate whether a cationic detergent (DTABr) has an active effect on the rate of formation of such complexes between 1,3,Strinitrobenzene (TNB) and the OH-ion.This aromatic substrate shows simple behaviour in sodium hydroxide solutions because there is no substitutable group (or leaving group) and the reaction isin which the 0 addition complex (TNBOH-) is stable in micellar solutions. We have already studied these reactions for several mixtures of water and methanol" and, depending upon the conditions of acidity used, we were able to describe several reaction processes. When the medium is strongly basic, the principal reaction is to give the o complex TNBOH-and only the rate constant k, may be determined experimentally. For a less basic range, the rate constant k-, is also accessible and corresponds to dissociation of the Meisenheimer complex, caused by thermal motion of solvent molecules. For strongly acid mixtures, dissociation occurs by direct attack and the reaction scheme is written as k,[H+l

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