Effects of head group size on the reaction methyl 4‐nitrobenzenesulfonate + Br− in water‐ethylene glycol cetyltrialkylammonium bromide micellar solutions

The reaction methyl 4‐nitrobenzenesulfonate + Br^? has been studied in water‐ethylene glycol cetyltrialkylammonium bromide (alkyl = methyl, ethyl, propyl, and butyl) micellar solutions by changing surfactant concentration as well as the weight percentage of ethylene glycol present in the bulk phase. The pseudophase model was adequate to rationalize quantitatively the micellar kinetic effects. Information about the influence of the head group size on the second‐order rate constant of the process and on the binding equilibrium constant of the organic substrate to the cationic micelles in water–ethylene glycol mixtures was obtained. Kinetic data taken from the literature were compared to those obtained in this work in order to examine the different effects produced by an alcohol that is localized in the bulk phase, such as ethylene glycol, with those caused by an alcohol that distributes between the bulk and micellar pseudophases, such as 1‐butanol. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 346–352, 2007     

Study of the reaction of methyl 4‐nitrobenzenesulfonate and Br− in water–glycerol cationic micellar solutions

The reaction of methyl 4‐nitrobenzenesulfonate (MNB) and Br^? has been studied in water–glycerol (GLY) alkyltrimethylammonium bromide micellar solutions, with the weight percentage of glycerol up to 50%. A pseudophase kinetic model was used for quantitatively discussing the kinetic data. Results showed that the equilibrium‐binding constant for the organic substrate molecules to the cationic micelles decreases upon increasing the amount of glycerol present in the micellar reaction media. The second‐order rate constant of the reaction in the micellar pseudophase is practically independent of wt% of GLY. Similar results were found in other water–organic solvent alkyltrimethylammonium bromide micellar solutions for the same process. However, the dependence of the reaction rate, for a given surfactant concentration, on the wt% of organic solvent is weaker for glycerol than for the other organic solvents. This was explained by considering that the cationic micellar ionization degree is nearly independent of wt% GLY. As a consequence, bromide ions concentration in the interfacial region (the reaction site) does not change by varying wt% of GLY. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 845–582, 2008     

Kinetics of the reaction of methyl 4‐nitrobenzenesul‐fonate + Br− in ethanol amine based surfactants

The kinetics of the reaction of methyl 4‐nitrobenzenesulfonate + Br^? ions has been studied in ethanol amine based (alkyldimethylethanolammonium bromide and alkyldiethylethanolammonium bromide) surfactant solutions. The observed first‐order rate constants increase monotonically with surfactant concentration, with hydrophobic chain length and with head group bulk in a manner similar to other quaternary ammonium surfactants. The results were analyzed using the pseudophase model of micellar rate effects in conjunction with a Langmuir form to describe micellar binding of bromide ion. An attempt to estimate activation parameters of the reaction from temperature variance of micellar pseudophase rate constants has also been made. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 303–308, 2006     

Study of the reaction Fe(CN)5(4‐CNpy)3− + S2O82− in aqueous salt and micellar solutions

The reaction Fe(CN)₅(4‐CNpy)³⁻ + S₂O₈²⁻ (4‐CNpy=4‐cyanopyridine) was studied in aqueous salt solutions in the presence of several electrolytes as well as in anionic, cationic, and nonionic surfactant solutions. In aqueous salt solutions the noncoulombic interactions seem to be important in determining the positive salt effects observed. The salting effects are influencing the activity coefficients of any participant in the reaction, including those ion pairs which can be formed between the anionic reagents and the cations which come from the added salts. The changes in surfactant concentration in anionic and nonionic surfactant solutions do not affect the reaction rate, which is similar to that in pure water at the same ionic strength. In cationic micellar solutions an increase in the rate constant compared to that in pure water is found; the reaction rate decreasing when the surfactant concentration increases. The kinetic trends can be explained assuming that the reagents are totally bound to the micelles and, therefore, an increase in the surfactant concentration results in a decrease in the reagent concentrations at the micellar phase and thus in a decrease in the observed rate constant. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 229–235, 1999     

Study of the reaction methyl 4‐nitrobenzene‐sulfonate + Cl− in mixed hexadecyltrimethyl‐ammonium chloride‐triton X‐100 micellar solutions

The reaction methyl 4‐nitrobenzenesulfonate + Cl^? was studied in hexadecyltrimethylammonium chloride (CTAC) in the absence and presence of 0.1 M NaCl, as well as in mixed CTAC/Triton X‐100 (polyoxyethylene(9.5)octylphenyl ether) aqueous micellar solutions with CTAC molar fractions of 0.9, 0.8, 0.7, and 0.6. Conductivity measurements were used to obtain critical micellar concentrations and micellar ionization degrees of the various micellar reaction media. From these data, thermodynamic information on the cationic/nonionic mixed micellar solutions was obtained. Micellar effects on the observed rate constant were explained by pseudophase kinetic models. The estimated second‐order rate constants in the micellar pseudophase of the different micellar reaction media showed that pure CTAC and mixed CTAC/Triton X‐100 micelles, at the high cationic surfactant molar fractions studied, provide reaction sites of similar characteristics at the interfacial region. This was in agreement with previous structural studies carried out on mixed CTAC/Triton X‐100 micellar solutions. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 45–51, 2003     

ESI activity of Br−, BF4−, ClO4− and BPh4− anions in the presence of Li+ and NBu4+ counter‐ions

To improve our understanding of the electrospray ionization (ESI) process, we have subjected equimolar mixtures of salts A⁺X⁻ (A⁺ = Li⁺, NBu₄⁺; X⁻ = Br⁻, ClO₄⁻, BF₄⁻, BPh₄⁻) in different solvents (CH₃CN, tetrahydrofuran, CH₃OH, H₂O) to negative‐ion mode ESI and analyzed the relative ESI activity of the different anionic model analytes. The ESI activity of the large and hydrophobic BPh₄⁻ ion greatly exceeds that of the smaller and more hydrophilic anions Br⁻, ClO₄⁻ and BF₄⁻, which we ascribe to its higher surface activity. Moreover, the ESI activity of the anions is modulated by the action of the counter‐ions and their different tendency toward ion pairing. The tendency toward ion pairing can be reduced by the addition of the chelating ligands 12‐crown‐4 and 2.2.1 cryptand and is, although to a smaller degree, further influenced by the variation of the solvent. Complementary electrical conductivity measurements afford additional information on the interactions of the ionic constituents of the sample solutions. Copyright © 2017 John Wiley & Sons, Ltd.     

Kinetics of MnO−4 oxidation of succinic acid in aqueous solution of cetyltrimethylammonium bromide

The rate of electron transfer from succinic acid to permanganate increases with an increase in the concentration of cationic surfactant, cetyltrimethylammonium bromide (CTAB). The micellar catalysis is attributed to the formation of an ion pair between CTAB subaggregates and reactants as well as an increase in the concentration (solubilization) of both reactants and/or intermediate in the micellar pseudophase. The effects of inorganic salts (MnCl₂, NaF, NaBr, and NaNO₃) have also been studied and discussed. The observed results are discussed in terms of the pseudophase model of the micelles proposed by Menger and Portony. Mechanisms consistent with the observed kinetic data have been proposed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 704–712, 2010     

Influence of the addition of alcohol on the reaction methyl-4-nitrobenzenesulfonate + Br(-) in tetradecyltrimethylammonium bromide aqueous micellar solutions

The reaction methyl-4-nitrobenzenesulfonate + Br(-) was studied in tetradecyltrimethylammonium bromide (TTAB) aqueous micellar solutions in the absence and in the presence of various amounts of n-hexanol, n-pentanol, and n-butanol. Kinetic micellar effects provoked by the addition of the linear alcohols can be rationalized by using simple pseudophase kinetic models. The equilibrium binding constants of the methyl-4-nitrobenzenesulfonate molecules to the cationic micelles decreases when [alcohol] increases. The (k(2)(m)/V(m)) values found are practically the same for the different TTAB-alcohol micellar solutions studied, independent of the nature and concentration of the alcohol present in the reaction medium. This has been explained by considering the balance of two factors operating on reactivity in opposite ways: (1). an increase in the volume of the micellar interfacial region upon increasing alcohol concentration, and (2). a decrease in the polarity of the interfacial region as the amount of alcohol present in the micellar solutions increases.     

Effects of cosolvents cetyltrimethylammonium bromide on the thresholds for nucleation of nitrogen in aqueous solutions

The decomposition of ammonium nitrite in water creates a supersaturated solution of nitrogen. The same process occurs in water-organic solvent mixtures. Acetone, dioxane, dimethylsulfoxide (DMSO) and dimethylformamide (DMF) are the cosolvents used in this study. The limits of supersaturation of nitrogen (C _SL /mol L^–1) were determined in all of these solvent mixtures by releasing the dissolved gas sonicationally and measuring the volume of released gas. C _SL was generally increased in the presence of cosolvents. The effectiveness sequence of organic solvents was found to be as DMF SL and all of the measured quantities of this study were generally affected by micelle formation.     

Study of the 1-chloro-2,4-dinitrobenzene + oh- reaction in tetradecyltrimethylammonium bromide aqueous micellar solutions

The 1-chloro-2,4-dinitrobenzene + OH^- reaction was studied in tetradecyltrimethylammonium bromide aqueous micellar solutions. Influence of changes in [surfactant] as well as in [NaOH] on the observed rate constant were rationalized by using pseudophase kinetic models. At high hydroxide ions concentration an additional pathway across the micellar boundary had to be considered. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of the fluoride ion on the aggregation and catalytic properties of micellar solutions of cetyltrimethylammonium bromide

The influence of the fluoride ion on the aggregation behavior and catalytic properties of neutral and alkaline aqueous solutions of cetyltrimethylammonium bromide in nucleophilic substitution reactions of phosphorus acid esters was studied by tensiometry, small-angle neutron scattering, and UV spectrophotometry. The critical micelle concentrations and the radii, aggregation numbers, and shape of micelles forming in these systems, as well as the kinetic parameters of the nucleophilic substitution reactions of phosphorus acid esters, were determined.     

Rheological and photorheological effects in aqueous solutions of cetyltrimethylammonium bromide containing 9-anthrylalkanols

Viscosities, flow properties, and static low-angle light scattering of dilute (250 mmol/dm³) aqueous micellar solutions of cetyltrimethylammonium bromide were measured in the presence of various amounts of 9-anthrylmethanol (AM), 2,2,2-trifluoro-1-(9-anthryl)ethanol (TFAE), 1-(9-anthryl)ethanol (AE), 9-methylanthracene (MA), and 9-ethylanthracene (EA). At room temperature the solubilization of AM induces an increase of viscosity and a rise in aggregation numbers (as determined from low-angle light scattering). Both features are reverted upon in in situ photodimerization of AM. After lowering the temperaure, non-Newtonian flow is detected by means of a rotating viscometer. The solubilization of AE and EA, respectively, leads to analogous observations, while no viscoelastic features were obtained with solubilized MA. TFAE containing systems at room temperature show non-Newtonian flow accompanied by viscoelasticity which can be ascribed to the formation of long rod-like micelles. Raising the temperature as well as photodimerization diminish the lengths of the micelles and the non-Newtonian features.     

Influence of cetyltrimethylammonium bromide on physicochemical properties and microstructures of chitosan-TPP nanoparticles in aqueous solutions

The nanoparticles of chitosan (CS) were prepared using pentasodium triphosphate (TPP) as a crosslinking agent and the influences of cetyltrimethylammonium bromide (CTAB) on the physicochemical properties of the CS-TPP nanoparticles were first studied by laser light scattering, zeta potential, and transmission electron microscopy (TEM). The concentration played a significant role in controlling the particle size of CS and the overlap concentration c(*) was testified to be about 1.0 mg/mL. The combination of static light scattering (SLS) and dynamic light scattering (DLS) allowed us to obtain more information about the CS-TPP nanoparticles in the presence of surfactant molecules. The addition of CTAB could reduce the hydrodynamic diameter of nanoparticles effectively in the salt solutions and simultaneously increase the zeta potential of the nanoparticles. The effect of CTAB concentration on the size of CS-TPP nanoparticle was also examined. The critical micelle concentration (CMC) of CTAB was used to interpret the complicated complex formed by the polyelectrolyte and the surfactant. Finally, TEM was used to observe the CS-TPP nanoparticles, which were affected by CTAB, to verify the results obtained by light scattering.     

Study of the ligand substitution reaction Fe (CN)5H2O3− + pyrazine in micellar solutions

The ligand substitution reaction Fe(CN)₅H₂O³⁻ + pyrazine → Fe(CN)₅ pyrazine³⁻ + H₂O has been studied in sodium dodecyl sulfate SDS, hexadecyltrimethylammonium bromide, CTAB, and salt aqueous solutions at 298.2 K. Kinetics were studied in dilute and concentrated salt solutions and in SDS and CTAB solutions at surfactant concentrations below and above the critical micelle concentration. Experimental results show that salt effects can be explained by considering the interaction between the cations present in the working media which come from the background electrolyte, and the Fe(CN)₅H₂O³⁻ species in the vicinity of the cyanide ligands. This interaction makes the release of the aqua ligand from the inner-coordination shell of the iron(II) complex to the bulk more difficult resulting in a decrease of the reaction rate when the electrolyte concentration increases. Kinetic data in surfactant solutions show that not only micellized surfactants are operative kinetically, but also nonmicellized surfactants are influencing the reactivity. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 377–384, 1997     

Standard partial molar volumes of alcohols in aqueous dodecyltrimethylammonium bromide solutions

Density measurements of water-dodecyltrimethylammonium bromide (DTAB)-alcohol ternary systems as a function of alcohol and surfactant concentrations were carried out at 25°C. The alcohols were propanol (PrOH), 2-propanol (2-PrOH) and hexanol (HexOH). The apparent molar volume V_,R of alcohols have been calculated and the standard (infinite dilution) partial molar volumes of alcohols V _R at each surfactant concentration were obtained by means of a least squares fit of V_,R vs. the alcohol concentration. The V _R vs. surfactant concentration curves have been rationalized in terms of the partial molar volume of alcohol in the aqueous V _f and the micellar V _b phases and the distribution constant of alcohol between the aqueous and the micellar phases K. The V _b values for PrOH and HexOH together with those of butanol and pentanol previously reported satisfy the additivity rule giving a methylene group contribution of 16.7 cm³-mol^–1 which is identical to that reported in the literature from the study of pure liquid alcohols. No difference between V _b for PrOH and 2-PrOH has been found. From density data of water-alcohol and water-surfactant binary systems and of water-surfactant-alcohol ternary system, the apparent molar volume of the surfactant in the water-alcohol mixed solvent V_,S have been calculated as a function of the surfactant concentration and of the mixed solvent composition. The effect of the alkyl chain length of the alcohols and the effect of isomerization of the alcohols on the V_,S vs. surfactant concentration trends have been analyzed.     

Kinetic evidence for the reaction of O•− radical ions and peroxodisulfate in alkaline aqueous solutions

Photolysis of S₂O₈⁼ in strong alkaline solutions (pH>13) in the presence of molecular oxygen yields ozonide radical ions, . These radicals show a complex decay rate sensitive to the peroxodisulfate concentration. A reaction mechanism, which includes the reaction of O^•− and S₂O₈⁼ with a rate constant k=(3−6)×10⁶M⁻¹s⁻¹ and accounts for the experimental results is discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 491–496, 1998     

Solvent effects on the rate of reaction of Cl2˙− and SO4˙− radicals with unsaturated alcohols

Rate constants have been measured in several aqueous/organic solvent mixtures for the addition reaction of Cl₂^˙? radicals with 2-propen-1-o1 and 2-buten-1-o1 as a function of temperature and with 2, 3-dimethyl-2-butene at room temperature. The rate constants were in the range of 10⁶–10⁹ L mol^?1 s^?1, the activation energies were relatively low (1–10 kJ mol^?1), and the pre-exponential factors varied over the range log A = 7.9 to 9.4. The rate constants (k) decreased (by up to a factor of 30) upon increasing the fraction of organic solvent and log k correlated linearly with the dielectric constant for a given water/organic solvent system, but the lines for the different solvent systems had different slopes. A better correlation of log k was found with a combination of the solvatochromic factor, E_T(30), and the hydrogen-bond donor acidity factor, α. This suggests that the rate of reaction is influenced by the solvent polarity and also by specific solvation of the ionic reactant and product. Solvent effect on the reaction of SO₄^˙? with 2-propen-1-o1 was studied for comparison. © 1993 John Wiley & Sons, Inc.     

Improved detection of salicylic acids using terbium-sensitized luminescence in aqueous micellar solutions of cetyltrimethylammonium chloride

The determination of salicylic, p-aminosalicylic and 5-fluorosalicylic acids was investigated using terbium-sensitized luminescence in aqueous solutions. Formation of a ternary chelate between terbium, EDTA and the salicylic acid requires dissociation of the phenol group which is adjacent to the dissociated carboxylic group. The reaction is obtained in alkaline solutions and is enhanced in the presence of cetyltrimethylammonium chloride. As evidenced by absorbance and fluorescence measurements, the cationic surfactant plays an important role in the formation of the ternary chelate and then terbium luminescence depends mainly on the extent of chelate formation. Linearity is found over more than four orders of magnitude and detection limits are in the range (2-4) x 10(-10) mol l-1 for the three acids.     

Synthesis of polymers in aqueous solutions: Synthesis of polysulfide by reaction of bis(4‐mercaptophenyl) sulfide with bis(4‐chloro‐3‐nitrophenyl) sulfone using various bases in aqueous solutions

The polycondensation of bis(4‐mercaptophenyl) sulfide (BMPS) with bis(4‐chloro‐3‐nitrophenyl) sulfone (BCNPS) was examined using various organic or inorganic bases in mixed solvents of N‐methyl‐2‐pyrrolidone (NMP) with water or in plain water. The reaction of BMPS with BCNPS proceeded smoothly to give the corresponding polysulfide in mixed solvents of NMP with water at 60 °C using 1,8‐diazabicyclo[5.4.0]undecene‐7 as a base, although the rate of the reaction decreased gradually as the water in the solvent increased. Polysulfide can also be obtained by reaction in plain water using appropriate organic bases such as tripropylamine (TPA) or quinoline. The polysulfide with a number‐average molecular weight of 45,100 was synthesized in 62% yield when the reaction of BMPS with BCNPS was performed using TPA as a base at 60 °C for 48 h in plain water. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3399–3404, 2000