A study was carried out on the solvolysis of the following substituted benzoyl chlorides in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane/water microemulsions: 4-CH 3 O, 3,4-(CH 3 O) 2 , 4-CH 3 , 4-H, 4-Cl, 3-Cl, 4-CF 3 , 3-CF 3 , 3-NO 2 , and 4-NO 2 . The benzoyl chlorides are found distributed between the isooctane and the interface, where they react with its hydration water. From the kinetic data we have been able to obtain the true rate constant for the reaction at the interface, k i . Two extreme types of behavior have been observed: for those processes which occur via a predominantly dissociative pathway, k i decreases together with W (W ) [H 2 O]/[AOT]), while for those processes which occur through a predominantly associative pathway, the rate constant at the interface, k i , increases as W decreases. The decrease of k i with W is interpreted as being due to the capacity of interfacial water for solvating the leaving Cl -. For the associative process, the increase in the nucleophilic capacity of the interfacial water as W decreases is the factor responsible for the increase in k i , so that the lesser capacity for solvation of the transition state can be compensated for as the water content of the microemulsion decreases. A comparative analysis of the reactivity of substituted benzoyl chlorides at the interface of the microemulsion shows an increase of the rate of the associative pathway and a decrease of the dissociative counterpart. Hence for W ) 50, the change between the two reaction pathways is observed for the benzoyl chlorides with substituents 4-Cl and 3-Cl, while in bulk water this change takes place with more electron-attracting substituents. When the water content of the microemulsion decreases (W ) 2), only the benzoyl chlorides 4-CH 3 O and 3,4-(CH 3 O) 2 will react predominantly through the dissociative pathway.

The kinetics of nitroso group transfer from 2-ethoxyethyl (EEN) and 2-bromoethyl (BEN) nitrite to the secondary amines piperazine (PIP), N-methylbenzylamine (NMBA), and morpholine (MOR) in bis(2-ethylhexyl) sulfosuccinate (AOT)/isooctane (iC8)/water microemulsions were determined. They are explained quantitatively in terms of a model in which the reagents are distributed among the aqueous, organic, and AOT film surfactant, with the aqueous pseudophase and the surfactant film as the loci of the reaction.

A kinetic study was carried out on the solvolysis of benzoyl bromide, BzBr, benzoyl chloride, BzCl, and benzoyl fluoride, BzF, in microemulsions of AOT/isooctane/water at 25 °C, where AOT is sodium bis(2-ethylhexyl)sulfosuccinate. In all cases, the pseudo-first-order rate constant, k obs, increases together with the [AOT] as a consequence of incorporating the substrates into the interface of the microemulsion. The application of a kinetic model based on the formalism of the pseudophase, which considers the distribution of the reagents between the continuous medium and the interface and that the reaction is taking place only at the interface, has enabled us to obtain the intrinsic values of the rate constant at the interface of the microemulsion for the three benzoyl halides, . The values of vary together with the water content of the microemulsion. The study of the variation of with W (W = [H2O]/[AOT]), the correlations with the E T polarity parameter, and the effect of the leaving group have allowed us to conclude that a mechanistic displacement has occurred along with the variation in W. For high water contents, the reaction occurs by an associative and dissociative path simultaneously, the relative weights of which depend on the leaving group, with the dissociative character increasing as the salient group of the benzoyl halide improves. As W diminishes, the associative path is favored as a consequence of an increase in the nucleophilicity of the water, and the dissociative path is disfavored due to the reduction in the capacity of the interfacial water to solvate the leaving group, X-. Consequently, a displacement of the reaction mechanism takes place from a dissociative extreme to an associative one as the water content of the microemulsion is reduced, which causes the sensitivity of the reaction to the nature of the leaving group to vary with W.

The kinetics of the solvolysis reactions of diphenylmethyl chloride, 4-nitrophenyl chloroformate, benzoyl chloride, anisoyl chloride, and bis(4-nitrophenyl)carbonate were studied in isooctane/SDS/1-hexanol/water and isooctane/TTABr/1-hexanol/water microemulsions with a constant [1-hexanol]/[surfactant] ratio of 5. The results were interpreted by means of a pseudophase model for (isooctane + hexanol)/(surfactant + hexanol)/water systems, the distribution of hexanol between isooctane and surfactant being calculated from previously published data. The intrinsic rate constant for the reaction in the interfacial pseudophase varied with the water content of the microemulsion droplets in a way that depended on both the nature of the surfactant and the mechanism of the reaction.

Changes, induced by aerosol-OT (sodium bis(2-ethylhexyl) sulfosuccinate, AOT), in the absorption spectrum of bromine, are shown to markedly depend on the nature and the hydration of the AOT-aggregates. A chargetransfer complex (CTC) between bromine and monomeric AOT (λ max ) 270 nm, 315 ) 1.4 × 10 3 cm -1 M -1 , and K ) 4 × 10 3 M -1 ) is observed in isooctane, in agreement with a very strong electron donor ability of AOT, attributed to its sulfonate headgroup. In "dry" reverse micelles ([AOT] > cmc), the constant for the CTC formation K ) 1.3 M -1 is markedly smaller. In aqueous reverse micelles, the observed decrease ( 315) is consistent with a competition between water and bromine in the stabilization of the AOT-head groups. Finally, in water-in-oil (w/o) microemulsions (W > 12), the complex disappears. The bromine-tribromide ion equilibrium is also investigated in AOT-w/o microemulsions in the presence of bromide ions. The marked dependence of the equilibrium constant for Br 3formation on the microemulsion composition (W) 12, K ) 178 M -1 ; W g 20, K ) 60 M -1 ; bulk water, K ) 16 M -1 ) is attributed to a change in the transfer free energy of bromide ion from bulk water to the aqueous pseudophase of the microdroplets (δ∆G tr (Br -) ) -2.6 and -1.3 kcal mol -1 for W ) 12 and 20, respectively). The results are discussed in terms of changes in the hydrogen-bond donor ability and polarity of water in AOT-w/o microemulsions.