The Kinetic Theory and the Mechanisms of Micellar Effects on Chemical Reactions

Martínek, Karel; Yatsimirski, A.K.; Levashov, Andrey V.; Березин, И.В.

doi:10.1007/978-1-4613-4157-4_1

Cited by 111 publications

(124 citation statements)

References 14 publications

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“…This model is similar to that developed by Berezin et al for treatment of bimolecular reactions of nonionic organic molecules. 13 The PIE treatment has been applied successfully to very many bimolecular reactions and indicates that the generalization regarding similarities of second-order rate constants in the micellar and aqueous pseudophases, which fits reactions of nucleophilic anions, is not universal, in that some reactions, e.g., anionic oxidations, are significantly slower in micelles than in water.…”

Section: Discussionmentioning

confidence: 99%

Micellar rate effects-assumptions and approximations

Bunton¹

2011

Arkivoc

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Surfactants with ionic or polar head groups and extended apolar groups form micelles in water with hydrocarbon-like interiors and ionic or polar groups at the surface and bind ionic and nonionic solutes. They act as reaction regions, i.e., as pseudophases distinct from the bulk solvent, and can accelerate or inhibit reactions, depending on rate constants and reactant concentrations in the two regions. Theoretical treatments and experimental evidence of reactant partitioning between water and micelles allow estimation of rate constants in the micellar pseudophase for both uni-and bimolecular reactions, provided that they are slower than reactant transfers between water and micelles, but some treatments apply only to dilute electrolyte. Competition between reactive and inert ions inhibits bimolecular ionic reactions and is treated by ion-exchange equations and some local ionic concentrations can be estimated by dediazonization trapping or physical methods. Ionic micelles affect rates of unimolecular and bimolecular watercatalyzed reactions because the reaction region at the micelle-water interface is less polar than water. Zwitterionic micelles have no net charge but they interact with ions, although ion-binding is weaker than with ionic micelles and there are limitations in the use of the theoretical treatments applied to ionic micelles. Micelles can control product composition, but product isolation limits use of surfactants in some reactions

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Section: Discussionmentioning

confidence: 99%

Micellar rate effects-assumptions and approximations

Bunton¹

2011

Arkivoc

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“…It is now generally accepted that this effect arises primarily from the concentration of both reactants in the small volume of the Stem-layer of micelles (1)(2)(3)(4)(5)(6).…”

Section: Introductionmentioning

confidence: 99%

Counterion micellar effects upon the reaction of low-spin diimine iron(II) complexes

Ortega¹,

Rodenas²

1989

Can. J. Chem.

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FRANCISCO ORTEGA and ELVIRA RODENAS. Can. J. Chem. 67,305 (1989).The rate of reaction of tris(1 , 10-phenanthroline)iron(II) ion (la), tris(3,4,7,8-tetramethyl-1 , 10-phenanthroline)iron(II) ion (lb), and tris(4,7-diphenyl-I, 10-phenanthroline)iron(II) ion (lc) with hydroxideion, in cationic micelles, is strongly affected by the concentration of micellar counterion in solution. The reaction of l a in CTACl is modestly speeded up by the addition of added KCI, while the reactions of 1 band l c are strongly inhibited by the addition of large amounts of KC1 and KBr to micellar solutions of CTACl and CTABr, respectively. These rate effects fit the pseudophase-ion exchange model, assuming the binding of the substrates to the micelles depends upon the counterion concentration.Key words: counterion micellar effects, low-spin diimine iron(I1) complexes.FRANCISCO ORTEGA et ELVIRA RODENAS. Can. J. Chem. 67,305 (1989).La vitesse de rtaction de l'ion hydroxyde avec les ions tris(phCnanthro1ine-l,lO)fer(II) (la), tris(tttramtthy1-3,4,7,8 phtnanthroline-l,lO)fer(II) (16) et tris(diphCny1-4,7 phenanthroline-l,lO)fer(II) (lc), dans des micelles cationiques, est fortement influencte par la concentration des contre-ions dans la solution micellaire. La vitesse de la rtaction du compose l a , dans le CTACI, est Itgerement plus rapide lorsqu'on ajoute du KCI; par ailleurs, les vitesses de rtaction des composts 1 b et l c sont fortement inhibees par l'addition de grandes quantitks de KC1 et de KBr a des solutions respectivement de CTACl et de CTABr. Si l'on fait l'hypothkse que la liaison des substrats aux micelles depend de la concentration du contre-ion, ces effets sur les vitesses des reactions sont en accord avec le modele d'echange ionique pseudophase.Mots cle's : effets des contre-ions dans des micelles, complexes de diimine fer(I1) << low-spin ,,.

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“…Reaction occurs in the water-rich region at the micellar surface (1)(2)(3)(4)(5)(6)(7)22) and involves a transfer of positive charge from the reaction center, in the micelle, to water molecules adjacent to its surface. This transfer should be more favorable in a cationic than in an anionic micelle.…”

Section: Discussionmentioning

confidence: 99%

Micellar effects upon reactions of the 2,2′,4,4′,4″-pentamethoxytrityl cation with nucleophiles

Bunton¹,

Cuenca²

1986

Can. J. Chem.

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Cationic micelles of cetyltrimethylammonium chloride and bromide (CTACl and CTABr) speed attack of water upon the 2,2',4,4',4'-pentamethoxytrityl cation by a factor of ca. 5. The first-order rate constant in water is 5.51 s-' at 25.0°C. Anionic micelles of sodium dodecyl sulfate (SDS) have little effect on this reaction, but they strongly inhibit attack of OH-. In water, second-order rate constants for attack of OH-, respectively, 235,177, and 2.8 x lo5 M-' s-'. Rate constants of reaction in CTACl go through maxima with increasing [surfactant] and analysis of the data shows that second-order rate constants at the micellar surface are similar to those in water. IntroductionAqueous ionic micelles speed bimolecular reactions of counterions by bringing substrate and ionic reagent together in the small volume of the micelles (1-6). The dependence of rate on [surfactant] can be treated quantitatively assuming that reactants are distributed between aqueous and micellar pseudophases, which are treated as distinct reaction media. Secondorder rate constants can be calculated for reaction in the micellar pseudophases, and for many bimolecular ionic reactions these second-order rate constants are similar to those in water. Thus the micellar rate enhancements are due largely to concentration of reactants in the micellar pseudophase.Reactions of dinitrohaloarenes with azide ion are major exceptions to this generalization, and second-order rate constants in cationic micelles are greater than those in water by factors of lo2-lo3 (7). We found similar large micellar effects for reactions of azide ion with hydrophobic N-alkyl-2-bromopyridinium ions. However, rate constants of deacylation and SN2 displacements by azide ion are similar in micellar and aqueous pseudophases (7), so that these unusual rate effects are not simply characteristic of azide ion as a nucleophile.Azide ion is very reactive towards carbocations, either preformed (8, 9) or generated in SN1 solvolyses (10, 11). The present investigation had the aim of comparing second-order rate constants for reaction of azide ion with a carbocation in water and micelles. Micellar effects upon nucleophilic addition to triarylmethyl dye cations have been well studied (12, 13), but we could not use such cations as Malachite Green or Crystal Violet because of the unfavorable equilibria with azide ion (14). The tri-p-anisylmethyl cation is also unsatisfactory, because it binds weakly to cationic micelles (13) and even in water the reaction is so fast that it can only be followed in very dilute azide

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The Kinetic Theory and the Mechanisms of Micellar Effects on Chemical Reactions

Cited by 111 publications

References 14 publications

Micellar rate effects-assumptions and approximations

Micellar rate effects-assumptions and approximations

Counterion micellar effects upon the reaction of low-spin diimine iron(II) complexes

Micellar effects upon reactions of the 2,2′,4,4′,4″-pentamethoxytrityl cation with nucleophiles

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