Reactions in Reverse Micelles

A systematic investigation of surfactants during the hydroformylation of higher olefins catalyzed by water-soluble Rh/TPPTS complexes (cf. Section 3.1.1.1), was conducted by Chen et al. [25]. The authors found that only cationic amphiphiles gave a significant effect on the yield and a moderate influence on the n/i ratio. 

The telomerization of 1,3-butadiene to octadienol (cf. Section 2.3.5) catalyzed by palladium phosphine complexes was realized in an aqueous micellar medium [26]. The micellar effects depend strongly on the type of surfactant and on the water solubility of the palladium complexes. 

Suzuki-type C-C-coupling reactions (cf. Section 2.11) with Pd phosphine complexes as catalysts can also be promoted by amphiphiles in an aqueous biphasic system (toluene/water). The amphiphile should have a phase-transfer function, with the best effect being observed with micelle-forming amphiphiles [27]. 

Reverse micelles are formed by the interaction of the polar head group of an amphiphile with colloidal water drops in an apolar medium. This represents an 

The first example is an asymmetric reduction of different phenyl alkyl ketones with sodium tetrsdiydroborate in an ephedrine-derived chiral reverse micelle [29]. The combination of R — n-C 2H25 in the ephedrinium salt and R = Ph, R = t-Bu in the ketone gave the best results with 84 % yield and 24 % ee. 

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The original work was on ionic reactions in normal micelles in water, but subsequently there has been extensive work on reactions in reverse micelles (O Connor et al., 1982, 1984 Kitahara, 1980 O. A. El Seoud et al., 1977 Robinson, et al., 1979). There also has been a great deal of work on photochemical and radiation induced reactions in a variety of colloidal systems, and microemulsions have been used as media for a variety of thermal, electrochemical and photochemical reactions (Mackay, 1981 Fendler, 1982 Thomas, 1984). 

Comparing the published synthesis reactions in reverse micelles, lipases seem to be the most stable enzymes in the microemulsion as reaction media and... 

Self-replicating micelles aqueous micelles and enzymatically driven reactions in reverse micelles. J. Am. Chem. Soc., 113, 8204-9. 

Bachmann, P. A., Walde, P, Luisi, P. L. and Long, J. (1991). Self-replicating micelles aqueous micelles and enzymatically driven reactions in reverse micelles. Journal of the American Chemical Society, 113, 8204-9. 

Recently, Zhang and Sun [64] reported the reduction of a series of phenyl alkyl ketones with NaBH4 to optically active alcohols in reverse micelles of different ephedrinium bromides. Addition of sugars hke D-fructose and D-glucose enhanced the stereoselectivity up to 27% ee. Other asymmetric catalytic reactions in reverse micelles have been investigated by Nozaki et al. [65] and Buriak and Osborn [66]. 

Enzymatic Reactions in Reversed Micelles at Low Solubilized Water Concentrations... 

Some Examples of Reactions in Reverse Micelles and Microemulsions... 

Part III deals with micellar catalysis, enzymology, and photochemical reactions in reversed micelles. 

TABLE 4 Third-Order Nonlinear Optical Properties of Polymers Synthesized by Enzyme-Catalyzed Reactions in Reverse Micelle Media... 

Bandyopadhyaya, R., Kumar, R., and Gandhi, K. S. 2000. Simulation of precipitation reactions in reverse micelles. Langmuir 16 7139. 

The determination of the enzyme activity as a function of the composition of the reaction medium is very important in order to find the optimal reaction conditions of an enzyme-catalyzed synthesis. However, the correlation between the reaction media properties and their effects on enzymatic reactions in reverse micelles is still unclear,... 

A few years later, the mechanism of a protease-catalyzed reaction in reverse micelles was for the hrst time elucidated by using stop-flow techniques and the a-chymotrypsin catalyzed hydrolysis of esters as model reaction [70], It was shown that deacylation remains rate limiting although in reverse micelle the acylation process is slowed down considerably. 

Liu, Z., Shao, M., Cai, R., Shen, P. 2006. Online kinetic studies on intermediates of laccase-catalyzed reaction in reversed micelle. J. Colloid Interface Sci. 294, 122-128. 

Schmidli, P.K., Luisi, P.L. 1990. Lipase-catalyzed reactions in reverse micelles formed by soybean lecithin. Biocatalysis 3, 367-376. 

Hakoda, M., Enomoto, A., Hoshino, T., Shiragami, N. 1996. Electroultrafiltration bioreactor for enzymatic reaction in reversed micelles. J. Ferment. Bioeng. 82, 361-365. 

Solubilization and catalysis in reversed micelles is the subject of a recent review by Kitahara [93] the literature to 1976 was covered by Fendler in his review [94] with emphasis on the extensive work from his own laboratories. Reactions in reversed micelles will not be simple reflections of reactions in normal micelles, but are bound to be influenced by the nature of the water in the interior of the micelles. The size of the pools of solubilized water will be determined by the ratio of surfactant to water and by the nature of the head groups of the surfactants which congregate together in the centre of these aggregates. The physical properties of the solubilized water has been found to be quite different from the properties of bulk water especially at low levels of hydration of the head groups [95]. At higher concentrations of water in the micelle interior the water behaves more like bulk water. Fluorescence probe analysis of the micellar core has indicated a very rigid interior state with a viscosity of over 40 cP [96-99]. 

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