Surfactants phase transfer catalysis with

Replacement of the organic phase with surfactants to exploit micellar phase transfer catalysis principles (Battal et al., 1997) for the alkylation of phenol and aniline. This group had previously demonstrated the synthesis of a surfactant by micellar autocatalysis, whereby the surfactant product itself catalyses the reaction (Kust and Rathman, 1995). 

Schomacker compared the use of nonionic microemulsions with phase transfer catalysis for several different types of organic reactions and concluded that the former was more laborious since the pseudo-ternary phase diagram of the system had to be determined and the reaction temperature needed to be carefully monitored [13,29]. The main advantage of the microemulsion route for industrial use is related to the ecotoxicity of the effluent. Whereas nonionic surfactants are considered relatively harmless, quaternary ammonium compounds exhibit considerable fish toxicity. 

One of the primary uses of modified electrodes has been In the area of electrochemical synthesis. Again the Increased solubilization by micelles and emulsions has been the primary Interest In using cationic surfactants. However, micelle and phase transfer catalysis and the hydrophobic nature of the electrode film has contributed to Increased yields. Table II shows a comparison of yields obtained In the electrooxidation of benz-hydrol in the presence of different surfactants and a comparison of the yields obtained with several other compounds with and without Ify-amlne 2389 (50). It can be seen that without a surfactant there Is no yield In aqueous solutions. Anionic and neutral surfactants which solubilize the compound but do not film the electrode cause only small Increases In yield, but the cationic film forming surfactant causes a sharp Increase in 3rleld. 

The kinetics and electronic mechanisms of conventional chemical catalysts- are contrasted with those in enzymes. The analogy between certain attributes of surfactants and phase-transfer catalysis and enzyme active sites are made and the limitations of surface catalysts and zeolites are pointed out. The principle features that give enz3nnes their unusual rate enhancements and remarkable specificity are discussed and ways in which these can be realized in man-made catalysts are proposed. The catalytic activation of CO2 by both enzymatic and non-enzymatic means, including a detailed analysis of the electronic reaction sequence for the metalloenzyme carbonic anhydrase, is used to illustrate the above themes. 

When the surfactant was sodium dodecyl sulfate, some butanol had to be present to achieve the microemulsion. A typical run used 2 mmol aryl iodide, 0.5 g surfactant, 1 mL butanol, 10 mL water, and 2 mmol base. The butanol was unnecessary with nonionic surfactants, such as the one derived from 1-dodecanol with 23 eq of ethylene oxide. The advantages of such a system include the following (a) No organic solvent is needed. The substrate is the oil phase, (b) The microemulsions form without the need for vigorous agitation, (c) No excess base is needed, in contrast with some reactions in which phase-transfer catalysis is used, (d) The surfactants can be recovered and recycled. They are inexpensive and biodegradable. 

Replacement of an hydroxyl group in resorcinol, most probably through tautomerism and imine formation, has been effected by heating it in an autoclave with 1-aminobutane and a small amount of phosphoric acid at 200°C under pressure (13 bar) for 8 hours. Only the monobutylamino substitution product was obtained but by phase transfer catalysis on the reaction product, with a benzyttrimethylammonium salt, (formed in situ from a surfactant and potassium iodide), sodium hydroxide solution and 1-bromobutane for 20 hours at 60-80°C, 3-dibutylaminphenol was produced in 64% yield (ref. 106). 

Okawara and coworkers (Ref. 10) first attempted to use phase transfer catalysis to modify a finely dispersed poly(vinyl chloride) powder in aqueous medium using nucleophiles such as azide, dithiocarbamate, or thiophenoxide ions in the presence of tetrabutyl ammonium salts. While a maximum conversion of 10% was obtained with the first two nucleophiles, thiophenoxide afforded a 30% conversion. Although the authors indicate that the reaction took place only at the surface of the polymer particles, the fairly high conversion obtained with thiophenoxide might suggest otherwise. A second report from the same laboratory (Ref. 11) focuses on reactions of poly(vinyl chloride) solutions with sodium azide in the presence of various catalysts. As expected, the reaction is strongly catalyzed by cationic surfactants such as dimethyl distearyl ammonium chloride or tetrabutyl ammonium chloride which both afford essentially complete conversion to the azido polymer. In contrast, tetrabutyl ammonium iodide is totally ineffective. 

It should be concluded that catalysis with surfactant assembfies is an active and successfirl area of research. In the case of emulsion polymerization, phase-transfer processes, and analytical apphcations, micellar methods are of practical importance. 

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