CTABr bromide

The members of Wolfbeis team constructed an optical sensor for ammonia-based on ion pairing76. They immobilized pH-sensitive dye (bromophenol blue) as an ion pair with cetyltrimethylammonium bromide (CTABr) in a silicone polymer matrix. Bromophenol blue, while contact the ammonia (both in water as well as in gaseous form) changes its color reversibly from yellow to blue. The immobilized dye shows long wave absorption with a good photostability. 

CTABr(OH) n-Hexadecyltrimethylammonium bromide (hydroxide) or cetyltrimethylammonium bromide (hydroxide)... 

Ci6H33NMe3 Br /. V Hexadecyltrimethylammonium bromide, HTABr Cetyltrimethylammonium bromide, CTABr 9 x 10 4... 

Deacylation or hydrolysis of chiral carbamates, carbonates and alkanoates Micelles and comicelles of N-hexadecyl-N-methylephedrinium bromide or N -myristoyl-histidine with CTABr. Rate effects and enantioselectivities examined Fomasier and Tonellato, 1984... 

A similar development in this direction is the synthesis of a mixed-phase material containing both micro- and mesopores (Ti-MMM-1) (223). This material was synthesized by the addition of organic templates for mesopores (cetyltrimethylammonium bromide, CTABr) and micropores (tetrapropylammo-nium bromide, TPABr) at staggered times and the variation of the temperature of a single reaction mixture. Ti-MMM-1 is more selective (for oxidation of cyclohexane and of n-octane) than either Ti-MCM-41 or TS-1. The powder X-ray diffraction pattern indicates that the material contains both MCM-41 and MFI structures. The mixed phase contains framework Ti species and more atomic order within its walls than Ti-doped MCM-41. 

The surface active agents (surfactants) may be cationic, anionic or non-ionic. Surfactants commonly used are cetyltrimethyl ammonium bromide (CTABr), sodium lauryl sulphate (NaLS) and triton-X, etc. The surfactants help to lower the surface tension at the monomer-water interface and also facilitate emulsification of the monomer in water. Because of their low solubility surfactants get fully dissolved or molecularly dispersed only at low concentrations and at higher concentrations micelles are formed. The highest concentration where in all the molecules are in dispersed state is known as critical micelle concentration (CMC). The CMC values of some surfactants are listed in table below. 

The effects of micelles of cetyltrimethylammonium bromide (CTABr), tetradecyl-trimethylammonium bromide (TTABr) and sodium dodecyl sulfate (SDS) on the rates of alkaline hydrolysis of securinine (223) were studied at a constant [HO ] (0.05 m). An increase in the total concentrations of CTABr, TTABr and SDS from 0.0 to 0.2 M causes a decrease in the observed pseudo-first-order rate constants (kobs) by factors of ca 2.5, 3, and 7, respectively. The observed data are explained in terms of pseudophase and pseudophase ion-exchange (PIE) models of micelles. Cationic micelles of CTABr speed attack of hydroxide ion upon coumarin (224) twofold owing to a concentration effect. ... 

Duynstee and Grunwald present some experimental data for Reaction (F) in the presence of hexadecyl trimethyl ammonium bromide (CTABr, C = cetyl) and sodium dodecyl sulfate (NaLS, L = lauryl). Sodium hydroxide was the source of OH" in all cases. A pseudo-first-order rate constant of 2.40 x 10-2 s-1 is observed for A CTABr. Use the following absorbance data to evaluate NaLS for this reaction ... 

The reaction of Problem 10 was studied at two different temperatures, and, from the temperature dependence of the rate constants, the authors determined AH% and ASJ, the enthalpy and entropy of activation, respectively. The following values of these parameters were obtained in pure water and in 0.01 M sodium dodecyl sulfate (NaLS) and 0.01 M hexadecyl trimethyl ammonium bromide (CTABr) ... 

Si02 0.0015 Ti(OEt)4 0.12 CTABr 0.26 TMAOH 24.3 H20 were CTABr is cetyltrimethylammonium bromide (from Aldrich), TMAOH is tetramethylammonium hydroxide (from Aldrich). The silica source was Aerosil-200 from Degussa and Ti(OEt)4 was supplied by Alpha Products. The crystallization was performed at 100°C for 48 hours in Teflon lined stainsteel autoclaves. The solid was recovered by filtration and exhaustive washing with distilled water until neutral pH in the filtrate was obtained. Then, the Ti-MCM-41 was dried at 60°C for 24 hours. The occluded surfactant was removed by calcination at 540°C in nitrogen for 1 hour and subsequently, for 5 hours in air. 

The effect of hexadecyltrimethylammonium bromide (CTABr)-based microemulsions on the decomposition of the /i-lactam antibiotic cephaclor (137) was described... 

According to Eq. (5-158), the reaction of l-fluoro-2,4-dinitrobenzene with pheno-late or thiophenolate ions is accelerated by micelles of cetyl-trimethylammonium bromide (CTABr) in aqueous solution by factors of 230 and 1100, respectively [404]. 

Most chemical studies in this field have eoncentrated on the effect of micellar surfactants on reaction rates and only a few attempts have been made to investigate the effect that micelles might have in altering the relative extent of competing reactions. For example, in studying the competitive hydrolysis and aminolysis of aryl sulfates in aqueous solution, Fendler et al. have found [407] that cationic micelles such as cetyl-trimethylammonium bromide (CTABr) are able to alter the balance between S—O bond fission and C—O bond fission as shown in Eq. (5-162). 

Bunton and co-workers [53] made a signiflcant contribution to reaction (6, X = halogen) by introducing cationic surfactants (detergents) which effectively catalysed the reaction of dinitrohalobenzenes with nucleophiles in aqueous solution by forming cationic mycelles. Cetyltrimethylammonium bromide and chloride (CTABr and CTAQ) were used. Thus Bunton and co-workers [54] reported that the reaction of 2,4-dinitrofluorobcnzene with C HsO" and CtHsS was catalysed by CTABr by factors 230 and 1100 respectively. Also... 

As by-product, diynes R C=C C=C R were formed [93]. (4) Finally, the animation of aryl bromides and chlorides with aliphatic and aromatic amines turned out to be possible in toluene/aq. KOH with Pd(Pt[ Bu)3]2) and CTABr at 90°C [94],... 

Kinetic treatments are relatively simple for spontaneous reactions, both unimolecular and bimolecular water-catalyzed reactions, because only the transfer equilibrium of the substrate between solvent and the association colloid has to be considered, Eq. (3). For example, the rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion (3) is a useful indicator of medium polarity, and reaction is inhibited by solvents that hydrogen bond to the carboxylate moiety [96]. The reaction is accelerated by a variety of colloidal species that incorporate 3. including ionic and zwitterionic micelles [97,98] and O/W microemulsions [99]. Reactions are slightly slower in microemulsions derived from cetyltrimethylammonium bromide (CTABr) than in the corresponding aqueous micelles, but changes in the alcohol cosurfactant or the hydrocarbon, or in their relative concentrations, do not have major rate effects, and it appears that these microemulsion droplets are similar to aqueous micelles as submicroscopic reaction media. These observations are consistent with estimates of surface polarities [99-101] determined with bound fluorescent probes [102]. 

Transfer equilibria of halide ions between bulk water and association colloids have been followed electrochemically, e.g., by use of specific ion electrodes or conductimetrically [61,62], or by chemical trapping (Sec. Ill) [65]. Bromide ion is an effective nucleophile in S, 2 displacements at all l centers, and rate constants in aqueous and alcohol-modified micelles and in O/W microemulsions have been analyzed quantitatively in terms of local concentrations of substrate and Br in the interfacial region of the colloid microdroplets [99,105]. The local second-order rate constants are typically slightly lower in the colloidal pseudophases than in water but are similar for micelles and microemulsions prepared with CTABr, indicating that interfacial regions provide similar kinetic media for these Ss2 reactions. However, reactions with the same overall concentrations of Br , or other ionic reactant, are slower in microemulsions or alcohol-modified micelles than in normal micelles for two reasons (1) The fractional ionization, a, is lower in the normal micelles and (2) the increased volume of the reaction region, due to the presence of cosurfactant, dilutes Br in the pseudophase provided by the association colloid [66,69,105]. 

Figure 5 Effect of added BuOH (O) and HexOH ( ) on interfacial concentrations (molarity) of water (H20nr) bromide ion Br i, and alcohol (R OHm) in 0.01 M CTABr, 0.01 M HBr at 40 0.EC. Note the scale changes on the y axis and for HexOH on the x axis. (From Ref. 65.)...

The cationic cetyltrimethylammonium bromide-hexanol-water system contains hexanol, which forms the organic phase and plays the role of cosurfactant. It has been mapped by Ahmad and Friberg [39] (see Fig. 1). Although possessing a large L2 domain, this microemulsion is capable of solubilizing only small amounts of water at low R values. The mciximum water dispersion appears at 2.16 m CTABr in hexanol for an R value of 44. 

Scattered reports are available in the chemical literature concerning the interactions of surfactants and cyclodextrins. For instance, Ise and coworkers [4] have reported on the interaction of colloidal electrolytes and cyclodextrins. They observed that the apparent critical micelle concentrations (cmc) of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTABr) increase upon the addition of ACD and BCD. They concluded that the cyclodextrins form 1 1 complexes with the surfactants. More recently Satake et al. [5] determined the association constants of ACD with several ionic surfactants. For 1-alkanesulfonate... 

However, the important criteria for WC to be implemented in fuel cells are its surface area, phase, and porosity. Ganesan and Lee reported that WC with a surface area of 170 m /g was obtained by thermal method, but the product tuned to be containing more sub-tungsten carbide (W2C) [70]. The latter was used to support Pt catalyst for methanol oxidation reaction. No test was done for ORR. Nevertheless, authors believed that oxide layer formed on carbide support is the key player in promoting alcohol oxidation by providing oxygen species as indicated by the decrease in desorption temperature of CO. In a different study carried out by the same group, mesoporous WC was synthesized and used as a support for Pt [71]. The mesoporosity was introduced by addition of surfactant like cetyltrimethylammonium bromide (CTABr). Catalyst performance was evaluated under identical conditions as previously stated however, no statement has been reported on ORR activity and electrochemical stability in both cases [70, 71]. 

The coulombic surfactant-inorganic (S-I) interaction was the first interaction used in the synthesis of mesoporous MCM silica materials. Likewise, early efforts for the synthesis of mesoporous TM oxides utilized the coulombic interaction as the primary S-I interaction. In these studies, cetyltrimethylammonium bromide (CTABr) as a cationic surfectant and sodium dodecyl sulfate (SDS) as an anionic... 

The effect of hydrotropes on the crossed Cannizzaro reaction rate of benzaldehydes with aqueous formaldehyde was investigated [67]. In the presence of polyethyleneglycol-200 the reaction rate of w-phenoxybenzalde-hyde increases more than six-fold and the w-phenoxybenzyl alcohol is also obtained with higher selectivity. The enhancement of the reaction rate of m-bromobenzaldehyde is lower than that observed for m-phenoxybenzaldehyde but the reaction selectivity is higher. p-Anisaldehyde and p-chlorobenzalde-hyde show an intermediate behavior. The cationic surfactants cetylpyri-dinium chloride and cetyltrimethylammonium bromide (CTABr) favor the Cannizzaro reaction instead of the crossed Cannizzaro one. 

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