Kinetics and mechanism for the reaction of 1-chloro-2,4-dinitrobenzene with n-butylamine and piperidine in AOT/n-hexane/water reverse micelles

Abstract

The kinetic profile of the S N Ar 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,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 S N Ar reactions in the interface were evaluated.

Kinetic Studies on the Nucleophilic Aromatic Substitution of Fluoronitrobenzene Derivatives with Polyvinylamine in Water Mediated by 2,6-O-Dimethyl-β-cyclodextrin

“…Thus, the nucleophilic aromatic substitution of water-soluble polymers with water-insoluble reagents is difficult to achieve because the micelle technique cannot be applied cleanly to polyelectrolytes. [8][9][10] In a related synthesis, Jang et al precipitated the polyallylamine polymer, and a dissolution in DMSO has also been carried out. 11 This method is impracticable for polyvinylamine because dissolution cannot be effected as the dried polymer only swells in DMSO or alcohol.…”

“…Higher molecular weight PVAm ( M n > 1500 g mol -1 ) is only soluble in water, which makes postderivatization reactions difficult because fluoronitroaromatic compounds are, for example, sparingly soluble or insoluble in water. Thus, the nucleophilic aromatic substitution of water-soluble polymers with water-insoluble reagents is difficult to achieve because the micelle technique cannot be applied cleanly to polyelectrolytes. − In a related synthesis, Jang et al precipitated the polyallylamine polymer, and a dissolution in DMSO has also been carried out . This method is impracticable for polyvinylamine because dissolution cannot be effected as the dried polymer only swells in DMSO or alcohol.…”

How the Nature of an Alpha-Nucleophile Determines a Brønsted Type-Plot and Its Reaction Pathways. An Experimental Study

“…Then, the nucleophilicity of the α-nucleophile added to the high nucleofugality of the LG of the heterocyclic ring suggests that the MC intermediate is not stable and the reaction mechanism proceeds through one TS structure and a concerted route is suggested. It is interesting to note that Kwan et al recently suggested that heterocycles that contain nitrogen atoms and good LG follow a concerted trend (Kwan et al, 2018) Furthermore, Campodonico et al proposed a concerted mechanism for the reaction of 2-chloro-5-nitro pyrimidine with primary and secondary alicyclic amines (Campodónico et al, 2020) Moreover, Bernasconi et al postulated that the existence of an intramolecular HB between a hydrogen atom of the nucleophilic centre (amine) and the o-NO 2 group of the substrate could explain the reactivity trend (Bernasconi et al, 2004;Ormazábal-Toledo et al, 2013b) In addition, computational reports based on experimental studies emphasize the role of HB on activating the reacting pair (electrophile/nucleophile) and stabilizing the TS (Bunnett and Morath, 1955;Zingaretti et al, 2003;Bernasconi et al, 2004;Gordillo et al, 2007;Alvaro et al, 2011;Ormazábal-Toledo et al, 2013b;Gallardo-Fuentes et al, 2014;Rohrbach et al, 2020) 2) The second trend (empty circles in Figure 1) shows the following order of reactivity: N-methyl hydroxylamine > N,Ndimethyl hydroxylamine > N,O-dimethyl hydroxylamine. This trend shows the decreasing effect of methyl groups on the nucleophilic reactivity; N-methylhydroxylamine is 2.3 times more reactive than N,N-dimethylhydroxylamine, which in turns is 4.6 times more reactive than N,O-dimethylhydroxylamine.…”