Non‐aqueous reverse micelles media for the SNAr reaction between 1‐fluoro‐2,4‐dinitrobenzene and piperidine

Abstract

AbstractThe kinetics of the nucleophilic aromatic substitution (SNAr) reaction between 1‐fluoro‐2,4‐ dinitrobenzene (FDNB) and piperidine (PIP) in ethylene glycol (EG)/ sodium bis (2‐ethyl‐1‐hexyl) sulfosuccinate (AOT)/n‐heptane and dimethylformamide (DMF)/AOT/n‐heptane non‐aqueous reverse micelle systems is reported. EG and DMF were used as models for hydrogen bond donor (HBD) and non‐hydrogen bond donor (non‐HBD) polar solvents, respectively. The reaction was found not to be base catalyzed in these media. A mechanism to rationalize the kinetic results is proposed in which both reactants may be distributed between the two environments. The distribution constants of FDNB between the organic and each micellar pseudophases were determined by an independent fluorescence method. These results were used to evaluate the amine distribution constant and the intrinsic second‐order rate coefficient of the SNAr reaction in the interface. The reaction was also studied in the pure solvents EG and DMF for comparison. The results in EG/AOT/n‐heptane at Ws = 2 give similar kinetic profiles than in water/AOT/n‐hexane at W = 10. With these HBD solvents, the interface saturation by the substrate is reached at around the same value of [AOT] and the intrinsic second‐order rate coefficient in the interface, k′b, has comparable values. On the other hand, when DMF is used as a polar non‐HBD solvent, the intrinsic second‐order rate constant increases by a factor of about 200 as compared to the values obtained using HBD solvents as a polar core. It is concluded that higher catalytic power is obtained when non‐HBD solvents are used as polar solvent in the micelle interior. Copyright © 2006 John Wiley & Sons, Ltd.