Cetylpyridinium bromide-catalyzed reaction of ortho-aminomethylphenols with para-nitrophenyldiphenyl phosphate

Cetylpyridinium bromide micelles accelerate the reaction of paranitrophenyldiphenyl phosphate with orthoaminomethylphenol by more than an order of magnitude in aqueous micellar solutions. The rate constants for this reaction are, however, about 50 times lower in the micellar phase than in water, i.e., the principal factor responsible for micellar catalysis in this reaction is concentration of the reagent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1126–1129, May, 1990.     

Micellar effect upon the reaction of hydroxide ion with coumarin

Cationic micelles of cetyltrimethylammonium bromide, CTABr, speed attack of hydroxide ion upon coumarin by a factor of c.a-2, due to a concentration effect. The first-order rate constants, k_obs, at a given hydroxide ions concentration go through maxima with increasing surfactant concentration. The overall micellar effects in these cationic micelles can be treated in terms of the pseudo-phase ion exchange model. Analysis of the data shows that second-order rate constant at the micellar surface is smaller than the second-order rate constant in water. Anionic micelles of sodium dodecyi sulfate, SDS, inhibit the same reaction. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 273–276, 1998.     

Kinetic regularities of micellar catalysis in the dephosphorylation with peroxide anion

The acid-base equilibrium of hydrogen peroxide in water solutions of cetyltrimethylammonium bromideand the reactivity of hydroxide and peroxide anions with respect to 4-nitrophenyl diethyl phosphate were investigated. In the micelles the acid ionization constant of the hydrogen peroxide increased three-fold. The application of the pseudophase distribution model under the conditions of competitive sorption of HO⁻ and HOO⁻ anions with the micelles of cetyltrimethylammonium bromide to the estimation of the main kinetic parameters of the micellar process was tested.     

Micellar Catalysis of Composite Reactions II. The Effect of CTAB Micelles on the Alkaline Fading of Malachite Green

The alkaline fading of malachite green, which is interpreted as parallel first order and second order reactions, has been studied in cetyltrimethylammonium bromide (CTAB) micellar solution at 25°C using spectrophotometry. A micellar catalytic model is proposed in this paper for constant concentration of hydroxideion. For this model, the first order and the second order rate constants in CTAB micellar phase,k_1m and k_2m have been obtained.

The experimental results indicate that the first order reaction of malachite green cation with water is catalysed by CTAB micelles while the second order reaction of malachite green cation with hydroxide ion is inhibited by CTAB micelles. The first order rate constant in CTAB micellar phase, k_1m , is 210 times of that in the bulk phase, but the second order rate constant in CTAB micellar phase, k_2m , is 0. 166 time of that in the bulk phase. The results are interpreted mostly in relation to the micellar micropolarity and electrostatic interaction. @Keywords: Micelle, Micellar catalysis, Parallel first order and seond order reactions, Malachite green     

Study of the Reaction 2-(p-Nitrophenyl)Ethyl Bromide + OH(-) in Sulfobetaine Aqueous Micellar Solutions in the Presence and Absence of Added Salts

The reaction of dehydrobromination of 2-(p-nitrophenyl)ethyl bromide with hydroxide ions has been studied in aqueous micellar solutions of N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, SB3-14. The kinetic effects of added salts (NaF, NaCl, NaBr, and NaNO(3)) on the reaction rate in SB3-14 aqueous micellar solutions have also been studied. They were rationalized by considering the binding of the anions, which come from the salt, to the sulfobetaine micelles and their competition with the reactive hydroxide ions for the micellar surface. The equilibrium binding constant of the 2-(p-nitrophenyl)ethyl bromide to the sulfobetaine micelles was estimated by recording the changes in the spectra of the organic substrate when the SB3-14 concentration in the micellar medium changed. This value was in agreement with that obtained from fitting of kinetic data. The second-order rate constant in the micellar pseudophase revealed that the reaction is faster in SB3-14 micelles than in water. This acceleration seems independent of the presence of added salts and can be explained by considering that SB3-14 micelles favor reactions in which charge is delocalized in the transition state. Copyright 2001 Academic Press.     

Micellar effects upon the reaction of hydroxide ion with 2-phenoxyquinoxaline

Cationic micelles of alkyltrimethylammonium chloride and bromide (alkyl = n? C₁₂H₂₅, n? C₁₄H₂₉, and n? C₁₆H₃₃) catalyze and anionic micelles of sodium dodecyl sulfate inhibit the reaction of hydroxide ion with 2-phenoxyquinoxaline (1). Inert anions such as chloride, nitrate, mesylate, and n-butanosulfonate inhibit the reaction in CTABr by competing with OH^? at the micellar surface. The overall micellar effects on rate in cationic micelles and dilute electrolyte can be treated quantitatively in terms of the pseudo-phase ion-exchange model. The determined second-order rate constants in the micellar pseudo-phase are smaller than the second-order constants in water. © 1994 John Wiley & Sons, Inc.     

Dynamics of micellar oligomeric and monomeric sodium 10-undecenoate

Multifield carbon-13 NMR longitudinal relaxation time measurements were used to probe the dynamics and structure of monomeric and oligomeric sodium 10-undecenoate in micellar solutions. Longitudinal relaxation data were fit to a two-state model for the spectral density function which utilizes as adjustable parameters a fast correlation time and an order parameter for each carbon atom, and an overall slow correlation time for the entire aggregate. This model was needed to explain the relaxation phenomena because of the anisotropic reorientation of the amphiphiles. The monomeric fast correlation profile indicated a motional gradient increasing toward the micellar core. Comparison of the fast correlation time profiles for monomer and oligomer revealed that the motional gradient found in the monomer was not present in the oligomer. Slow correlation times extracted from the two-state model indicate that the radii of the oligomeric micelles, approximated from the Debye—Stokes—Einstein equation, are slightly larger than the monomeric micelles: 10.6 versus 9.4 Å, respectively. Radii calculated using self-diffusion coefficients also are larger for the oligomeric micelles: 13.4 Å for oligomeric micelles and 10.6 Å for the monomeric micelles. The values determined for the micellar radii are less than that for the extended monomeric chain, 14.7 Å.     

Interfacial Composition of Surfactant Aggregates in the Presence of Fragrance: A Chemical Trapping Study

In recent years, there has been increasing interest in daily-use chemical products providing a pleasant scent. The added fragrance molecules may induce microstructural transitions of surfactant aggregates, which further affect the physical and chemical properties of the products. Here, the effects of four types of aromatic alcohols (cinnamyl alcohol, phenyl ethanol, phenyl methanol and anisyl alcohol) on cetyltrimethylammonium bromide (CTAB)/KBr aggregates were studied. The combined results from rheology, dynamic light scattering, and transmission electron microscopy measurements showed that cinnamyl alcohol induced significant micellar growth, while increases in micellar growth were less obvious for the other aromatic alcohols. The changes in the interfacial molarities of water, aromatic alcohol, and bromide ions during such transitions were studied using the chemical trapping method. Transitions resulting from added cinnamyl alcohol were accompanied by significant declines in interfacial water and bromide ion molarities, and a rise in interfacial alcohol molarity. The marked decrease in interfacial water molarity was not observed in previous studies of the octanol induced formation of wormlike micelles and vesicles, indicating that a different mechanism was presented in the current system. Nuclear magnetic resonance investigation showed that π–π stacking between cinnamyl alcohols, but not cation–π interactions between alcohols and CTAB headgroups, facilitated the tight packing of alcohol molecules in CTAB aggregates and the repulsion of water from the interfacial region. The current study may provide a theoretical basis for the morphological regulation of surfactant aggregates in the presence of additives.     

Micellar effects upon electron transfer from ferrocenes

The oxidations of ferrocene (FcH) and n-butylferrocene (FcBu) by ferric salts (nitrate or bromide) are strongly inhibited by aqueous cetyltrimethylammonium bromide and nitrate (CTABr and CTANO₃, respectively). The kinetics of inhibition fit a model in which the substrates are distributed between water, and the micelles and binding constants K_s to the micelle can be estimated. The oxidations are strongly catalyzed by micelles of sodium lauryl sulfate (NaLS), and the kinetics can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase and the rate constants in that pseudophase, which for both substrates are very similar to those in water. Some added salts reduce the micellar catalysis by excluding ferric ions from the micelle. The oxidations of FcH and FcBu by ferricyanide ions are too fast to be followed in water, but they are inhibited by anionic micelles of NaLS. By analyzing the rate surfactant profiles using independently measured values of K_s the second-order rate constants in water have been estimated.     

Spectroelectrochemical and spectrophotochemical properties of N-tetradecyl-N '-ethyl-viologen: Micellar effects

The results of Spectroelectrochemical studies in homogenous solutions have shown that below the cmc value the cation radical of N-tetradecyl-N '-ethyl viologen (TDEV) dimerizes. The TDEV and tetradecyltriethyl-ammonium bromide (TDEA) micelles were found to stabilize the cation radical TDEV^.+ and increase the rate constant for the reaction TDEV+TDEV²⁺ = TDEV^.+ as compared with the results obtained at concentrations below cmc.Based on the spectrophotochemical measurements for TDEV it was found that the quantum yield (Φ) of photoreduction in micellar evironment of TDEA was twice as large as Φ for reactions performed in homogenous solution. Moreover, in micellar solutions photoreduction of TDEV leads to a cation radical of reduced TDEV (TDEV⁺), but in homogenous solution to the dimer of TDEV [TDEV]₂. Therefore, the process of dimerization of TDEV^.+ cation radical is inhibited by micellar catalysis.     

Role of structural factors in micellar-catalyzed solvolysis of phosphonates

Conclusions The catalytic effect of cetyltrimethylammonium bromide in the solvolysis of phosphonates depends on the nature of the substrate. The increase in reaction rate upon transition from water to the micellar phase is determined by the effectiveness of interaction of the phosphates with the micelles and by the region of their localization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 530–533, March, 1984.     

A kinetic method to estimate dissociation degrees of micellar aggregates in TTAB–alcohol aqueous micellar solutions

The reactions of dehydrochlorination of 1,1‐trichloro‐2,2‐bis(p‐chlorophenyl)ethane, DDT, and 1,1‐dichloro‐2,2‐bis(p‐chlorophenyl)ethane, DDD, with hydroxide ions were studied in various TTAB–alcohol (TTAB = tetradecyltrimethylammonium bromide) aqueous micellar solutions as a function of alcohol content. The alcohols used were heptanol, hexanol, pentanol, butanol, isobutanol, tert butanol, propanol and isopropanol. Kinetic data show that the dissociation degree of the micelles is the main factor controlling reactivity in all the TTAB–alcohol micellar solutions. This fact permits the development of a kinetic method in order to estimate the dissociation degree of the micellar aggregates present in the alcohol–TTAB aqueous micellar solutions. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 204–209, 2000     

Partial molar volume of dodecyltrimethylammonium hydroxide in water and NaOH aqueous solutions

 The partial molar volume of dodecyltrimethylammonium hydroxide in water and aqueous NaOH solutions was measured. The addition of NaOH did not affect either the micellized or the unmicellized molecules. The expansion on micellization is much larger than in dodecyltrimethylammonium bromide systems, which reflects the stronger ionization of the hydroxide surfactant micelles, when compared with that of the bromide amphiphile. Received: 27 October 1997 Accepted: 4 March 1998     

Physicochemical studies of the cetyltrimethylammonium bromide micellar system using a bromide selective electrode

The use of the bromide selective electrode in physicochemical studies of the cationic micellar system of cetyltrimethylammonium bromide (CTAB) is described. Potentiometric methods and appropriate equations have been developed and used to determine the critical micellar concentration, the ionization degree, and the apparent ion-exchange constants of various anions (fluoride, chloride, hydroxide, acetate, nitrate, sulfate and borate). The interaction of the cationic micelles of CTAB with various species [the lipophilic reagent 1-fluoro-2,4-dinitrobenzene, the anionic succinate and the cationic tris-(hydroxymethyl)-aminomethane] was monitored through the measurement of the changes in the concentration of the free bromide counterions.     

Kinetics of alkaline fading of methyl violet in micellar solutions of surfactants: Comparing Piszkiewicz's,Berezin's,and pseudophase ion-exchange models

The micellar effect of surfactants of various types on the rate of the reaction between methyl violet and hydroxide ion is studied. The absorption spectra show that the cation of methyl violet is bound by micelles of all types at proper concentrations of surfactants. The observed rate constant in micellar systems containing nonionic Brij-35, zwitterionic 3-(dimethyldodecylammonio)-propanesulfonate, cationic cetyltrimethylammonium bromide and hydroxide surfactants is higher, whereas in solutions of the anionic surfactant sodium dodecylsulfate is lower than that one in the surfactant-free system. Piszkiewicz's, Berezin's, and pseudophase ion-exchange models of the kinetic micellar effect are used for the treatment of the dependences of the above-mentioned constants on the surfactant concentration. The values of the corresponding kinetic parameters are compared and discussed. The influence of nonionic, zwitterionic, and anionic micelles on the reaction rate is discussed on the basis of medium and concentration kinetic effects. The character of the cationic micelles effect is somewhat paradoxical. Although the observed pseudo–first-order reaction rate constant substantially increases in the presence of such micelles, the second order-rate constant in these micelles is lower than the corresponding value in surfactant-free aqueous solution. As a possible explanation, the decrease in the reactivity of the HO^– ions is proposed, owing to their electrostatic association with the cationic headgroups (“diverting effect”).     

Quasielastic neutron scattering measurements of monomer molecular motions in micellar aggregates

Quasielastic neutron scattering measurements have been made on some micellar aggregates. It is shown that the observed spectra arise almost exclusively from monomer motions in the aggregates. Two illustrative systems were studied, direct micelles of tetradecyl trimethyl ammonium bromide in water, and reverse micelles of aerosol OT in cyclohexane with different amounts of water solubilised inside the micellar core. For the aerosol OT micelles, the translational diffusion is fast (8×10^?10 m².sec^?1) and independent of the size of the water pool. Rotational correlation times are of the order of 4×10^?11 sec. At high water contents the water in these pools is similar to bulk aqueous electrolytic solutions. For the tetradecyl trimethyl ammonium bromide micelles the translational diffusion constant was found to be 5×10^?10 m².sec^?1.     

The influence of hydrophobic amines on hydrolysis of bis(p-nitrophenyl) methylphosphonate in micellar solutions of cetylpyridinium bromide

The kinetics of hydrolysis of bis(p-nitrophenyl) methylphosphonate in the presence of primary aliphatic amines in aqueous micellar solutions of cetylpyridinium bromide was studied. The reaction proceedsvia two routes, alkaline hydrolysis and amine-catalyzed hydrolysis according to the general basic catalysis mechanism. The contributions of these routes and the catalytic effect of micelles depend on the hydrophobicity of the amines. The formation of different types of micelles was found, and their characteristic parameters were determined by tensiometry and high-resolution¹H NMR spectroscopy with a magnetic field pulse gradient. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 2, pp. 267–272, February, 2000.     

Rheological properties of the aqueous mixtures of cationic-anionic surfactants

The rheological properties of the aqueous mixtures of cationic-anionic surfactants, both in single-phase systems and in aqueous two-phase systems, have been studied. Bizarre rheological properties —negative thixotropy, viscoelasticity and hihg viscosity of shear rate dependent at relatively low concentration — have been observed. An unusual viscosity change, that is, viscosity lowering with increasing concentration, was obtained. The negative thixotropy might be due to the existence of lamellar or sheet-like micelles, viscoelasticity might be induced by rodlike and lamellar or sheet-like micelles, the high viscosity might be a consequence of the formation of network by long rodlike micelles and the concentration-induced viscosity lowering could be interpreted in terms of the decrease of micellar dimensions with concentration.     

Hydration of dodecyltrimethyl-ammonium hydroxide micelles

 The hydration of dodecyltrimethylammonium hydroxide (DTAOH) micelles was determined by viscosity measurements, giving 39.2±7.0 water molecules per micellized dodecyltrimethylammonium ion. This result is lower than the hydration of DTAB micelles, which is about 65. This difference may be due to the effect of the electrorestrictive structure-making hydroxide ion on the hydration of the alkyltrimethylammonium head group, in comparison with the less hydrated structure-breaking bromide ion. Received: 29 January 1996 Accepted: 4 July 1996     

THE EFFECT OF SURFACTANT MICELLES ON THE ALKALINE HYDROLYSIS OF DIMETHYLFORMAMIDE

The alkaline hydrolysis of dimethylformamide has been studied at 40'C in micellar solutions of single surfactant (CTAB. SDS. Brij 35) with the analog thermoanalytical curve method of thermokinetics. A kinetic equation of micellar catalysis under the condition of highter reactant concentration than micellar concentration ([S]>[M]) has been derived from the pseudophase model of micellar catalysis and some relative assumptions, The kinetic parameters. k_m, k_2mand the association constant of reactant with micelle K₁, have been calculated in this way. the results indicate that these surfactant micelles exhibit catalytic effect on the reaction. This is attributed to the micropolarity and local concentration effect of micelles.