Ammonium salts cetyltrimethylammonium bromide

Fig. 10.8 A where the R substituents are alkyl or heterocyclic radicals to give compounds such as cetyltrimethylammonium bromide (cetrimide), cetylpyridinium chloride and benzalkonium chloride. Inspection of the stmctures of these compounds (Fig. 10.8B) indicates the requirement for good antimicrobial activily of having a chain length in the range Cg to Cig in at least one of the R substituents. In the pyridinium compounds (Fig. 10.8C) three of the four covalent links may be satisfied by the nitrogen in a pyridine ring. Polymeric quaternary ammonium salts such as polyquatemium 1 are finding increasing use as preservatives.

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]. 

In bromination of anilines, the ortholpara ratio is significantly increased in presence of cetyltrimethylammonium bromide (CTAB) but is not altered with a symmetrical ammonium salt (TBAB). Surprisingly, increasing steric hindrance in the ortho position by N-alkylation has resulted with higher ortho-selectivity. This phenomenon is linked to the orientation of the aniline at the surface of the micellar aggregates1017. 

Many other quaternary ammonium salts, commercially available, work equally well (e.g., cetyltrimethylammonium bromide). 

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. 

Many quaternary ammonium salts containing one or two large alkyl groups, such as cetyltrimethylammonium bromide, C16H33N (CH3)3Br, produce micelles as well as being phase transfer agents. Indeed, there are borderline cases where a particular quaternary ammonium salt may behave as both a surfactant and a phase transfer catalyst or as either one, depending on the particular reaction conditions. Starks (6) discusses further similarities and essential differences of the two phenomena. The most important difference is that whereas the rate of phase transfer catalysed reactions are directly... 

The closeness of fit may be gauged from the experimental and theoretical rate vs. concentration curves for hydrolysis of p-nitrophenyl carboxylates catalysed by quaternary ammonium surfactant micelles (Figure 3). The shape of the curve is satisfactorily explained for unimolecular, bimolecular, and termolecular reactions. An alternative speculative model is effectively superseded by this work. Romsted s approach has been extended in a set of model calculations relating to salt and buffer effects on ion-binding, acid-dissociation equilibria, reactions of weakly basic nucleophiles, first-order reactions of ionic substrates in micelles, and second-order reactions of ionic nucleophiles with neutral substrates. In like manner the reaction between hydroxide ion and p-nitrophenyl acetate has been quantitatively analysed for unbuffered cetyltrimethylammonium bromide solutions. This permits the derivation of a mieellar rate constant km = 6-5 m s compared to the bulk rate constant of kaq =10.9m s . The equilibrium constant for ion-exchange at the surface of the micelle Xm(Br was estimated as 40 10. The... 

Several chemocatalytic systems for sulfoxidation that employ other oxidants than hydrogen peroxide, molecular oxygen, or alkyl hydroperoxide have been reported. Manganese-catalyzed oxidation of sulfides with iodosobenzene (PhIO) using chiral Mn(salen) complexes was used to obtain chiral sulfoxides in up to 94% ee [71]. PhIO was also employed as the oxidant in sulfoxidations catalyzed by quaternary ammonium salts [72]. The use of cetyltrimethylammonium bromide (n-Ci6H33Me3N Br ) gave the best result, and with 5-10 mol% of this catalyst, high yields (90-100%) of sulfoxide were obtained from various sulfides. 

It is clear from the numerous accounts in literature that DMCs can efficiently catalyze the copolymerization of CO2 and epoxides. DMCs can however also be used to develop systems that selectively catalyze the CO2 cycloaddition rather than the copolymerization (Scheme 1.4) as is illustrated by the work of Dharman et al. [20]. By itself, a Zn-Co-DMC is an efficient catalyst for the copolymerization reaction. However, the addition of a quaternary ammonium salt to the reaction mixture switches the selectivity of the catalytic system toward the exclusive formation of the cyclic carbonate. The quaternary ammonium ion plays two important roles in the catalytic system it accelerates the diffusion of CO2 into the reaction mixture and it favors a backbiting mechanism. As such, it hinders the growth of the polymer chain and it enables the selective cyclic carbonate production. Although most zinc-containing catalysts for this reaction are very sensitive toward water, Wei et al. have shown that, for example, the combination of Zn-Co-DMC with CTAB (cetyltrimethylammonium bromide) could even use water-contaminated epoxides as an epoxide feed [21]. 

Hao et al. [119] studied sodium perfluorooctanoate (SPFO) and cetyltrimethylammonium bromide (CTAB) mixed solutions by H-NMR. The results indicated a strong interaction between oppositely charged head groups and the penetration of SPFO molecules into the CTAB micelles. Monduzzi et al. [120] identified lyotropic crystalline phases of the ammonium salts of perfluo-ropolyether carboxylic acids by H- and " N-NMR spectroscopy. 

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