Microheterogeneous Solvation for Aminolysis Reactions in AOT‐Based Water‐in‐Oil Microemulsions

García‐Río, Luis; Mejuto, J. C.; Pérez‐Lorenzo, Moisés

doi:10.1002/chem.200401067

Cited by 22 publications

(16 citation statements)

References 46 publications

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“…Other reactions that can illustrate this case are the aminolysis of NPA in AOT-based microemulsions by piperazine and sarcosine [20]. In this case, the fit of the pseudophase model equation to the experimental results was satisfactory.…”

Section: Reactions Taking Place Simultaneously In Two Phases: Reactiomentioning

confidence: 58%

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Microemulsions as microreactors in physical organic chemistry

García‐Río

Leis

Mejuto

et al. 2007

Pure and Applied Chemistry

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Microemulsions are very versatile reaction media which nowadays find many applications, ranging from nanoparticle templating to preparative organic chemistry. The thermodynamically stable and microheterogeneous nature of microemulsions, used as reaction media, induces drastic changes in the reagent concentrations, and this can be specifically used for tuning the reaction rates. In particular, amphiphilic organic molecules can accumulate and orient at the oil-water interface, inducing regiospecificity in organic reactions. In this review, we will show the recent tendencies of the use of microemulsions as organic reaction media.

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Section: Reactions Taking Place Simultaneously In Two Phases: Reactiomentioning

confidence: 58%

“…Other examples of this case are the aminolysis of NPA by n-decylamine [20] and N-methyl-benzylamine [21] (Scheme 5) or the nitrosation of N-methyl-benzylamine by ethoxy-ethyl-nitrite and bromo-ethyl-nitrite (RONO) in water/AOT/isooctane microemulsions [17] (see Scheme 4).…”

Section: Reactions Taking Place In One Phase: Reaction At Aot Filmmentioning

confidence: 98%

Microemulsions as microreactors in physical organic chemistry

García‐Río

Leis

Mejuto

et al. 2007

Pure and Applied Chemistry

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“…From Scheme and using the distribution constants of 2‐nitroaniline defined in terms of molar ratios as shown in Equations (1 a and b) [10] :, the following expression is obtained for absorbance as a function of the composition parameter Z of the microemulsion, Z= [isooctane]/[NaOT]. Note that the concentrations in Equations (1a and b) are in relation to the total volume of the system 11. Considering that the absorbance A at any wavelength is due to that exhibited by 2‐nitroaniline in each microenvironment of the colloidal system, Equation (2) is obtained (for a full derivation see http://www.wiley-vch.de/contents/jc_/<~CRYR>/_s.pdf): where ${\varepsilon _0 }$ and ε i are the molar absorptivities of 2‐nitroaniline in the continuous medium and the interface of the w/o microemulsion, and ${K_{\rm{o}}^{\rm{w}} = K_{{\rm{oi}}} /K_{{\rm{wi}}} }$ .…”

Section: Methodsmentioning

confidence: 99%

Acidity Function of Water‐in‐Oil Microemulsions

Fernández¹,

García‐Río²

2006

ChemPhysChem

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Three compartments are available for the localization of small solutes in water-in-oil (w/o) microemulsions: [1][2][3] 1) the internal aqueous core or water pool, 2) the micellar interface formed by a monolayer of surfactant molecules with their polar head groups oriented toward the water pool, and 3) the external organic phase. The existence of these microenvironments is the basis of their use as reaction media, [4] due to their capacity to solubilize and compartmentalize substrates with different properties. Likewise, these systems are a promising reaction medium for the deactivation of mustard and nerve agents [5] and an alternative to phase-transfer catalysis. [6] One of the problems arising from their use as reaction media is their destabilization by additives needed for the reactions to take place. The amount of solubilized water is affected by the addition of electrolytes. [7] The maximum amount of water solubilized in NaOT-based microemulsions (NaOT = sodium salt of bis(2-ethylhexyl)sulfosuccinate) in the presence of electrolytes increases up to the optimal ionic strength, and then decreases with increasing ionic strength. These results are interpreted in terms of salting-in and salting-out phenomena, as well as the counteracting effects of attractive intermicellar interaction and interfacial bending stress.[8] This problem can be overcome by using surfactants with reactive counterions, where the surfactant itself can act as a source of H + to give a strongly acidic medium that can be used for deactivation reactions.Here we report the results obtained for a w/o microemulsion in which the Na + surfactant counterion is replaced by H + to give a system with a strongly acidic character. We show that the acidic properties of this new microemulsion is controlled by simply modifying the water-to-surfactant molar ratioThe use of the H 0 acidity function of the dispersed phase of the microemulsion is of crucial importance in understanding the properties of this system as a reaction medium. HOT [9] was prepared from NaOT by ion exchange using Amberlite IR 120 (plus) resin. We checked the extent of Na + /H + exchange by two methods: atomic absorption spectroscopy showed the absence of Na + in the HOT sample (the residual Na + content is consistent with a degree of Na + /H + exchange of greater than 99 %), and acid/base titration, which also indicated that the extent of Na + /H + exchange is greater than 99 %. All other reagents used were supplied by Aldrich at the highest level of purity available and were used without further purification. Absorption spectra were recorded with a Varian Cary 50 spectrophotometer fitted with thermostatically controlled cell holders at 25.0 8C. To determine the distribution constant of 2-nitroaniline between water and isooctane (K The compositions of the w/o microemulsions for this study were selected to cover a wide range: the NaOT content varied between 6 and 30 wt %, water between 0.5 and 43 wt %, and that of isooctane between 29 and 93 wt %. These composition intervals allowe...

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“…Recently, we have shown its application to aminolysis reactions occurring both in the aqueous microdroplet and at the interface of AOTbased microemulsions. 16 Equivalent expressions to those derived by us were obtained by Casavino and co-workers and applied to iron(III) oxidation of some alkyl-substituted ferrocenes 17 and the kinetics of substitution in palladium(II) complexes. 18 Sánchez et al have shown that the Brönsted equation, which can be derived directly from the transition state theory, is an alternative to the pseudophase model to rationalize the observed kinetic effects in microemulsions.…”

Section: Introductionmentioning

confidence: 88%

“…29 Thus, we can estimate that the decrease in the rate constant is 23 times on going from the aqueous medium to the interface of the microemulsion, an inhibition that is entirely consistent with the behavior observed for other aminolysis reactions in AOT-based microemulsions. 16 2. Reaction in the Continuous Medium.…”

Section: Methodsmentioning

confidence: 99%

First Evidence of Simultaneous Different Kinetic Behaviors at the Interface and the Continuous Medium of w/o Microemulsions

2005

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A study was carried out on the butylaminolysis reaction of 4-nitrophenyl caprate in AOT/chlorobenzene/water microemulsions, with the observed rate constant, kobs, showing both first- and second-order dependence on butylamine concentration. The first-order term in [BuNH2] is due to the reaction occurring at the interface of the microemulsion while the second-order term is due to the reaction in the continuous medium. The different kinetic behavior is accounted for by the mechanism by which the reaction proceeds: at the interface of the microemulsion, the rate-determining step is the formation of the addition intermediate, T+/-, whereas in the continuous medium the slow step is the base-catalyzed decomposition of this intermediate. The application of the pseudophase formalism allows the observed kinetic behavior to be explained and to obtain the rate constants at the interface, ki2=0.13 M-1 s-1, and in the continuous medium, ko2KT=2.46x10(-2) M-2 s-1. These values indicate that the reaction rate decreases approximately 23 times upon going from the aqueous medium to the interface of the microemulsion, whereas the rate constant in the continuous medium is consistent with that obtained in pure chlorobenzene, ko2KT=2.09x10(-2) M-2 s-1.

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Microheterogeneous Solvation for Aminolysis Reactions in AOT‐Based Water‐in‐Oil Microemulsions

Cited by 22 publications

References 46 publications

Microemulsions as microreactors in physical organic chemistry

Microemulsions as microreactors in physical organic chemistry

Acidity Function of Water‐in‐Oil Microemulsions

First Evidence of Simultaneous Different Kinetic Behaviors at the Interface and the Continuous Medium of w/o Microemulsions

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