Cetyltrimethylammonium bromide, action

Phase transfer catalyzed reactions in which ylides are formed from allylic and ben-zylic phosphonium ions on cross-linked polystyrenes in heterogeneous mixtures, such as aqueous NaOH and dichloromethane or solid potassium carbonate and THF, are particularly easy to perform. Ketones fail to react under phase transfer catalysis conditions. A phase transfer catalyst is not needed with soluble phosphonium ion polymers. The cations of the successful catalysts, cetyltrimethylammonium bromide and tetra-n-butylammonium iodide, are excluded from the cross-linked phosphonium ion polymers by electrostatic repulsion. Their catalytic action must involve transfer of hydroxide ion to the polymer surface rather than transport of the anionic base into the polymer. Dicyclohexyl-18-crown-6 ether was used as the catalyst for ylide formation with solid potassium carbonate in refluxing THF. Potassium carbonate is insoluble in THF. Earlier work on other solid-solid-liquid phase transfer catalyzed reactions indicated that a trace of water in the THF is necessary (40). so the active base for ylide formation is likely hydrated, even though no water is included deliberately in the reaction mixture. 

Further light on enzyme action is shed by micelles of amphiphilic molecules, which catalyse many chemical reactions and are often regarded as very simple models for enzymes ( amphiphilic and micelle are defined in Section 14.0). The disposition of hydrophobic (inside) and hydrophilic (outside) groups in a micelle resembles that of enzymes. Like enzymes, too, micelles are denatured by heat or urea, and they show specificity towards substrates (Jencks, 1969). Reactions that liberate anions, e.g. the hydrolysis of esters, are catalysed by cationic micelles, e.g. those of cetyltrimethylammonium bromide 14J6)... 

Cationic surface active agents such as benzalkonium chloride and cetyltrimethylammonium bromide (Figure 1) have use as antibacterial agents, i.e., disinfectants and antiseptics, and have the advantage that the antimicrobial action is combined with a cleaning action associated with their detergent activity. 

Cationic surfactants such as dodecylammonium chloride (DAC), cetyltrimethylammonium bromide (CTAB), and dodecyltrimethylam-monium bromide (DTAB) are much less frequently used than anionic surfactants due to their relatively inefficient emulsifying action or adverse effects on initiator decomposition. In addition, the cationic surfactants are much more expensive than anionic surfactants. 

Pure cationic surfactants such as cetyltrimethylammonium bromide (CTAB) have been used extensively for research into the fundamental physical chemistry of their surface activity. Such investigations have led to a vast improvement in our basic understanding of the principles of surfactant action. Because of the significant differences in purity and composition between commercial- and research-grade materials, however, care must be taken not to overlook the effects of such differences on the action of a given surfactant in a specific application. 

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