Organic Reactions in Functional Micelles

The general emphasis in this work is to compare the reactivity and selectivity of function-bearing micelles in catalysis with their simple counterparts. TThe pattern of research has been guided by the analogy of enzymic catalysis, and surfactants carrying the common prosthetic groups of protease enzymes have been synthesized. Most studies have been concerned with acyl transfer from reactive esters, and several authors have sought to demonstrate co-operativity between different catalytic sites. 

The simplest example of a functional micelle is (49), previously demonstrated to be more effective than its trimethylammonium analogue in both esterolysis and bimolecular elimination reactions. It has now been demonstrated that micelles of (49) are more effective catalysts for the hydrolysis of p-nitrobenzoyl phosphate dianion at high pH than non-functional surfactants. 2,4-Dinitrochloro- and fluoro-benzene react with micelles of (49) at high pH 10 times faster than with hydroxide ion at a comparable external pH. The initial product is (50) and this in turn is hydrolysed in micelles 2.6 x 10 times faster than is 2,4-dinitrophenyl 2-(trimethylammonium)ethyl ether in water at pH 12. Acyl transfer between p-nitrophenyl acetate and (49) gives an intermediate whose hydrolysis is not micelle catalysed. In contrast to the rate acceleration observed in that case, hydrolysis of p-nitrophenyl acetate is inhibited by micelles of (51) since the phenoxide nucleophile is weak and at the reaction pH its micelles are zwitterionic, not cationic. Synthesis of functional choline-type micelles is facilitated by the use of sulphonate (52), which is reactive towards thiophenoxide in aqueous micelles, but its water-insoluble trifluoromethanesulphonate reacts with a range of anions under phase-transfer conditions.  

Figue 5 Selectivity in the reaction of surfactant esters with surfactant alkoxides 

The Jenisalem group have produced a range of papers on choline- 

Surfactant peroxyanions are more effective nucleophiles than their alkoxy-or acyloxy-counterparts both in micelles, and below the critical micelle concentration. In an attempt to generate the micellar peracid (55), Brown and Darwent reacted the corresponding p-nitrophenyl ester (56) with hydrogen peroxide and observed that the production of p-nitrophenolate ion was far from first-order in (55). It proved possible to simulate the results in terms of a scheme in which the initieilly formed peracid anion reacts with (56) to form a diacyl peroxide, which is then attacked by hydrogen peroxide anion to give two molecules of (55). At the sub-miceUar concentrations employed it was estimated that reaction between (55) and (56) occurred 10 faster than might be 

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