Cetyltrimethylammonium bromide oxide

Equation (1) is generally used to estimate the rate constant, kin the micellar pseudophase, but for inhibited bimolecular reactions it provides an indirect method for estimation of otherwise inaccessible rate constants in water. Oxidation of a ferrocene to the corresponding ferricinium ion by Fe3 + is speeded by anionic micelles of SDS and inhibited by cationic micelles of cetyltrimethylammonium bromide or nitrate (Bunton and Cerichelli, 1980). The variation of the rate constants with [surfactant] fits the quantitative treatment described on p. 225. Oxidation of ferrocene by ferricyanide ion in water is too fast to be easily followed kinetically, but the reaction is strongly inhibited by anionic micelles of SDS which bind ferrocene, but exclude ferricyanide ion. Thus reaction occurs essentially quantitatively in the aqueous pseudophase, and the overall rate depends upon the rate constant in water and the distribution of ferrocene between water and the micelles. It is easy therefore to calculate the rate constant in water from this micellar inhibition. 

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 metal-catalysed autoxidation of alkenes to produce ketones (Wacker reaction) is promoted by the presence of quaternary ammonium salts [14]. For example, using copper(II) chloride and palladium(II) chloride in benzene in the presence of cetyltrimethylammonium bromide, 1-decene is converted into 2-decanone (73%), 1,7-octadiene into 2,7-octadione (77%) and vinylcyclohexane into cyclo-hexylethanone (22%). Benzyltriethylammonium chloride and tetra-n-butylammo-nium hydrogen sulphate are ineffective catalysts. It has been suggested that the process is not micellar, although the catalysts have the characteristics of those which produce micelles. The Wacker reaction is also catalysed by rhodium and ruthenium salts in the presence of a quaternary ammonium salt. Generally, however, the yields are lower than those obtained using the palladium catalyst and, frequently, several oxidation products are obtained from each reaction [15]. 

The oxidation of chalcogen compounds by hypervalent iodine reagents is a known procedure. The oxidation of sulfides only leads to the formation of mixtures of sulfoxides and sulfones under drastic conditions. Usually only sulfoxides are formed and can be obtained in excellent yields [46-48]. Recent investigations showed that sulfide oxidation can be catalyzed by quaternary ammonium salts in micellar systems. Iodosobenzene 5 is catalytically activated by cetyltrimethylammonium bromide (CTAB) and the sulfoxides 24 can be obtained in high yields under very mild conditions, Scheme 6 [49]. Other micelle forming surfactants have also been employed, but CTAB showed the best results in this reaction. It is also possible to perform such oxidations to sulfoxides with (terf-butylperoxy)iodanes of type 13 [50]. 

An alternative method for asymmetric and metal-free sulfoxidation was explored by Kita et al. [133], In their approach, iodosylbenzene (Ph-I02) was used as oxidant in reversed micelles formed by cetyltrimethylammonium bromide (CTAB) in toluene. From the numerous chiral inductors tested, tartaric acid derivatives proved best. In the presence of 10 mol% bis(2-methoxybenzoyl)tartaric acid, methyl (4-nitrophenyl)sulfide was converted into the sulfoxide in 91% yield and with 72% enantiomeric excess [133],... 

Wacker oxidation. The oxidation of 1-alkcnes to methyl ketones by oxygen catalyzed by PdCk and CuCU can be carried out under phase-transfer conditions with cetyltrimethylammonium bromide or a closely related salt as the phase-transfer catalyst. Yields are in the range 50-75%. Several rhodium and ruthenium complexes can be used as the metal catalyst, but the yields are lower. 

Several reports exist on the effect of metal cations on satin hydrolysis (Wagner-Jauregg et al., 1955 Gustafson and Martell, 1962 Epstein and Mosher, 1968). Some of the metal ions that appear to be effective include Cu(ll), Au(ll), Ag(l), Ni(ll), and Zn(ll). The effect of hypochlorite on sarin decomposition has been studied (Epstein et al., 1956), including the effect of surfactant micelles on the process (Dubey et al., 2002). It was shown that the use of cetyltrimethylammonium bromide substantially increased the speed with which satin was destroyed by hypochlorite. The effect of surfactant on the oxidation of sarin (and other OPs) with o-iodosobenzoic acid has been examined (Hammond et al., 1989). As part of an extensive study of the reactivity of nerve agents, Larsson (1958a) conducted a study of hydrogen peroxide s reaction with sarin. 

The Fe-Au nanoparticles were reported to consist of metallic cores, having an average diameter of 6.1 nm, surrounded by an oxide shell, averaging 2.7 nm in thickness, for a total average particle diameter of 11.5 nm [101]. A surfactant solution is prepared with nonylphenol poly(ethoxylate) ethers. Au-coated Fe nanoparticles were also prepared in a reverse micelle formed by cetyltrimethylammonium bromide (CTAB), 1-butanol and octane as the surfactant, the co-surfactant and the oil phase, respectively [100]. The nanoparticles were prepared in aqueous solutions of micelles by reduction of Fe(II) and Au precursors with NaBH4. The typical size of the nanoparticles is about 20 nm. The existence of Fe and Au is again confirmed by energy dispersive X-ray microanalysis. 

FIG. 14 Initial rates of adsorption (dF/dt)0 of cetyltrimethylammonium bromide (CTAB) onto indium tin oxide (ITO) as a function of externally applied potential, at two pH values ( , pH 5.6 o, pH 9). Concentration CTAB 0.5 mM, background electrolyte I0 M KCI. (Unpublished data of EJ.M. Bollen and J.M. Kleijn, Wag-eningen University.)... 

Although isomerization of alkenes occurs simultaneously with the oxidation, rhodium and ruthenium complexes can also be used instead of palladium for the oxidation of terminal alkene [15]. With these catalysts, symmetrical quaternary ammonium salts such as tetrabutylammonium hydrogensulfate are effective. Interestingly, the rate of palladium-catalyzed oxidation of terminal alkenes can be improved by using poly(ethylene glycol) (PEG) instead of quaternary ammonium salts [16]. Thus, the rates of PEG-400-induced oxidation of 1-decene are up three times faster than those observed with cetyltrimethylammonium bromide under the same conditions. Interestingly, internal alkenes can be efficiently oxidized in this polyethylene glycol/water mixture. 

Also, in the study of Peng et al. [369], the mesoporous titanium dioxide nanosized powder was synthesized using hydrothermal process by applying cetyltrimethylammonium bromide as surfactant-directing and pore-forming agent. They synthesized and applied this nanoparticle for the oxidation of Rhodamine B (see Table 6). 

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