Abstract
The kinetic profile of the SNAr reaction of 1-chloro-2,4-dinitrobenzene with n-butylamine and piperidine in AOT/n-hexane/water reverse micelles were investigated as a function of variables such as AOT and amine concentration and the amount of water dispersed in the reverse micelles, Wo = [H2O]/[AOT]. The reactions in the micellar medium are faster than in the pure solvent. The pseudo-first order rate constants of the reactions go through a maximum when the AOT concentration is increased. Micellar interface saturation and no further micellar catalysis occurs at c.a. 0.1M of AOT. At higher AOT concentration dilution of the reactants in the micelles is the responsible of the rate decrease. In micellar medium a significant lost in the catalysis is observed compare with pure n-hexane. Thus, the reactions effectively take place at the interface of the aggregates. The kinetic behavior can be quantitatively explained taking into account the distribution of the substrate and the nucleophile between the bulk solvent and the micelle interface. A plausible mechanism to explain the results is proposed. Both the reactants distribution constants, between the micellar pseudo-phase and organic solvent, and the intrinsic second-order rate coefficients of SNAr reactions in the interface were evaluated.
Highlights
The reactivity of bimolecular reactions is affected by reverse micelles mainly through the increase in local reactant concentrations within the small micellar volume, and through changes in the rate limiting transition state energy
The kinetic profile of the SNAr reaction of 1-chloro-2,4-dinitrobenzene with n-butylamine and piperidine in AOT/n-hexane/water reverse micelles were investigated as a function of variables such as AOT and amine concentration and the amount of water dispersed in the reverse micelles, Wo = [H2O]/[AOT]
In this work we extend the kinetic study to the reaction of a related substrate CDNB, less prone to base catalysis than FNDB, with n-butyl amine (NBA) and piperidine (PIP)
Summary
The reactivity of bimolecular reactions is affected by reverse micelles mainly through the increase in local reactant concentrations within the small micellar volume, and through changes in the rate limiting transition state energy. Both the reactants distribution constants, between the micellar pseudo-phase and organic solvent, and the intrinsic second-order rate coefficients of SNAr reactions in the interface were evaluated.
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