Cetyltrimethylammonium bromide CTABr

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. 

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

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 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. ... 

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]. 

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. 

The area covered by the fluorinated surfactant Monflor 71 molecule, 0.26 nm, is much smaller than the area, 0.47 nm , covered by a similar hydrocarbon surfactant, cetyltrimethylammonium bromide (CTABr), molecule. The small area covered by the adsorbed fluorinated surfactant reveals very tight packing at the interface. 

Khan, M.N. Effects of cetyltrimethylammonium bromide (CTABr) micelles on the rate of the cleavage of phthaUmide in the presence of piperidine. Colloids Surf. A 2001,181, 99-114. 

Another experimental example, which could demonstrate the importance of the so-called empirical criteria described in the beginning of this section, is the kinetic study of alkaline hydrolysis of 4-nitrophthalimide (NPT) in the absence and presence of cationic micelles (cetyltrimethylammonium bromide, CTABr micelles) at 35°C. The pH-independent and pH-dependent rate of alkaline hydrolysis of NPT in the absence and, presumably, in the presence of micelles involve the reaction of HO with nonionized (SH) and ionized (S ) NPT, respectively Pseudo-first-order rate constants (kobs) for hydrolytic cleavage of NPT at 0.01-M NaOH, 35°C and varying total concentrations of CTABr ([CTABrlx), as listed in Table 7.14, have been treated with Equation 7.76 where [D ] = [CTABrlx - CMC, Ks is CTABr micellar binding constant of NPT, k and k, represent pseudo-first-order rate constants for hydrolysis of NPT in the aqueous pseudophase and micellar pseudophase, respectively. The nonlinear least-squares calculated values of k, . Kg, and least squares (Sd ) are shown in Table 7.14. The values of k ai are comparable with the corresponding kobs values within the domain of the acceptable residual errors dj (Table 7.14). 

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