Micellar effects on the ionization of carboxylic acids and interactions between quaternary ammonium ions and aromatic compounds

Bunton, Clifford A.; Minch, Michael J.

doi:10.1021/j100608a010

Cited by 94 publications

(52 citation statements)

References 5 publications

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“…The meaning of pH, and the role of buffers in aqueous surfactants are not fully understood. However, little change in pH, even with a relatively low buffer concentration (acetate), was observed 5 in aqueous CTAB if the ionic strength was maintained high with NaCl as in the present work. In addition it is known 6 that changes in the ionic equilibria of buffers, owing to the presence of cationic surfactants, can be minimized by using hydrophilic buffers such as those used in this work.…”

Section: Ketonization Reactions In Buffer Solutionssupporting

confidence: 43%

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Keto–enol interconversion of 2-phenacylfuran in aqueous solution and in the presence of surfactant micelles

Maria¹,

Fontana²,

Siani³

et al. 2002

Arkivoc

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Dedicated to Professor Domenico AbstractThe equilibrium constants for the keto-enol tautomerism of 2-phenacylfuran (2PF),, have been determined in water and in aqueous solutions of CTAB (cetyltrimethylammonium bromide) by combining the pK a KH for ionization of the ketone, directly measured in aqueous NaOH solutions, and the pK a EH for ionization of the enol, obtained from the corresponding rate profile of ketonization. Comparison of these equilibrium constants with those reported for some previously studied phenylacetyl-and phenacyl-heterocycles highlights the effect of an adjacent furyl group on keto-enol tautomerism. Moreover, it has been shown that micelles from cationic (CTAB) and zwitterionic propanesulfonate] surfactants decrease the rate of ketonization of the enolate of 2PF and/or increase the apparent acidity of the keto form. These effects have been related to the affinity of the surfactant micelles for the enolate of 2PF. To the contrary, anionic surfactants (SDS: sodium dodecyl sulfate) do not display appreciable effects on the acidity of the keto form or on the kinetics of ketonization of the enol form of 2PF.

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Section: Ketonization Reactions In Buffer Solutionssupporting

confidence: 43%

“…For the significance of pH in aqueous solutions of CTAB see ref. 5. Each profile shows two regions in which the reaction is pH-independent and a region for OH -catalysis.…”

Section: Ph-profilementioning

confidence: 99%

Keto–enol interconversion of 2-phenacylfuran in aqueous solution and in the presence of surfactant micelles

Maria¹,

Fontana²,

Siani³

et al. 2002

Arkivoc

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“…This equilibrium is the product of the partial equilibria [8] and [9]: Ka, w [8] NR'H, NR, + H, ' and K, [9] NR, + S, 2 NR, where K, is the pH-independent association constant of NR, with similarly charged micelles (16) and is related to K,,, and Ke by [I01 K, = K,,, (1 + [Hw+l/Ka,w) and L111 Ke=Ks.K,,w A direct determination of K, for the base form of neutral red is difficult as the indicator is unstable in strong basic medium, the condition required for the same. The equilibrium constants K, and Kc calculated for neutral red with cationic micellar systems at various pH are included in Table 1 For neutral red in cationic micellar medium:…”

Section: Resultsmentioning

confidence: 99%

Association of neutral red with micelles and its effect on the pK_a

Dutta¹,

Bhat²

1993

Can. J. Chem.

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The interactions of neutral red with cationic surfactants, viz., N-hexadecylpyridinium chloride and alkyltrimethylammonium bromides; a nonionic surfactant, viz., Triton X100; and an anionic surfactant, viz., sodium dodecyl sulfate, were investigated spectroscopically. The equilibrium constants for the association of the indicator with the micelles were determined from the apparent association constants at constant pH at 298 K. The effects of the indicator-micelle association on the apparent pKa of the indicator in aqueous surfactant solutions are discussed. It was shown that the apparent pKa of the indicator in cationic surfactant solution can be predicted from knowledge of the indicator-micelle association constant.

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“…Various studies using a variety of techniques such as rheological approaches, [7][8][9][10][11][12] birefringence, 8 NMR, 4,5,8,13,14 heat capacity, 15 acidity, 13 neutron reflectivity, 6 surface tension, 16 and SANS measurements 4,17,18 have been performed on the influence of organic counterions on cationic surfactants. It has been demonstrated that aromatic counterions are more effective at lower concentrations than salts or electrolytes in inducing the micellar growth, 6,13,19 which can be attributed to interactions with the aromatic π-electron system.…”

Section: Introductionmentioning

confidence: 99%

Impact of Phenolic Antioxidants on Structural Properties of Micellar Solutions

et al. 2006

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Antioxidants solubilized in micellar solutions can change micellar properties like the size and shape of micelles, critical micellar concentration (cmc) and viscosity. Interactions arising between antioxidants and the surfactant determine the locations of antioxidants and vice versa. The location and interaction are dependent on the type of both the antioxidant and surfactant. Influences of various antioxidants on the physical and structural properties were tested in micellar systems of cationic CTAB, non-ionic Brij 58 and anionic SDS. The antioxidants used to investigate the effects of gradually increasing lipophilicity were gallic acid (GA) and the gallate esters from methyl to octyl gallate (MG-OG). Hydroxy cinnamic acids (HCAs) like p-coumaric acid (pC), caffeic acid (CA), ferulic acid (FA) and sinapic acid (SA) were employed to observe effects of functional groups like hydroxyl and methoxy groups. Micellar size and shape determined by small angle neutron scattering (SANS), viscosity and cmc were chosen to characterize the antioxidant influence. In Brij 58 systems propyl gallate (PG) did not affect the cmc or aggregation number but decreased micellar size slightly due to an intercalation of PG into the region of the polyoxyethylene chain and the first adjacent alkyl chain methylene groups. In SDS systems the micellar size and cmc decreased in the presence of PG. This was attributed to PG residing in the Stern layer. However, in CTAB systems micelles swelled at low PG concentration and in the presence of GA, while higher PG concentrations and more lipophilic antioxidants led to a sphere-to-rod transition with a simultaneous increase in viscosity and decrease in cmc. This revealed the intercalation of antioxidants in the palisade layer of CTAB micelles entering into strong interactions of electrostatic and hydrophobic origin. It could be demonstrated that the interactions became stronger the more lipophil an antioxidant is and the more hydroxyl groups are attached to the aromatic ring. Differences in the location and interaction of antioxidant and micelles are proposed as being responsible for the effectiveness of antioxidants.

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Micellar effects on the ionization of carboxylic acids and interactions between quaternary ammonium ions and aromatic compounds

Cited by 94 publications

References 5 publications

Keto–enol interconversion of 2-phenacylfuran in aqueous solution and in the presence of surfactant micelles

Keto–enol interconversion of 2-phenacylfuran in aqueous solution and in the presence of surfactant micelles

Association of neutral red with micelles and its effect on the pK_a

Impact of Phenolic Antioxidants on Structural Properties of Micellar Solutions

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Micellar effects on the ionization of carboxylic acids and interactions between quaternary ammonium ions and aromatic compounds

Cited by 94 publications

References 5 publications

Keto–enol interconversion of 2-phenacylfuran in aqueous solution and in the presence of surfactant micelles

Keto–enol interconversion of 2-phenacylfuran in aqueous solution and in the presence of surfactant micelles

Association of neutral red with micelles and its effect on the pKa

Impact of Phenolic Antioxidants on Structural Properties of Micellar Solutions

Contact Info

Product

Resources

About

Association of neutral red with micelles and its effect on the pK_a