ORGANIC-REACTIONS IN MICRO-ORGANIZED MEDIA - WHY AND HOW

Organic reactivity in microorganized media is illustrated by results o n micellar catalysis in micelles and on the properties of water in rev erse micelles. With cationic micelles, interesting catalytic effects o n reactions between hydrophobic and hydrophilic reagents are obtained when the hydrophilic partner, and only it, goes into the Stern layer b y shifting the counter-ions of the surfactant. Results on nucleophilic substitution of a lipophilic phosphoric triester, PNDPP, by an oximat e, MeCO-C(Me)=NO-, in the presence of various cationic surfactants, ce tyltrimethylammonium salts, CTAX, with X-=Br-, Cl- and AcO-, and of va rious buffers, glycine or carbonate, exemplify how the ion exchanges a t the micellar interface control the interfacial nucleophile concentra tion and the reactivity. In anionic AOT-reverse micelles, alkene bromi nation, a water-promoted reaction between two lipophilic reagents, is taken as a probe for the chemical properties of the sodium-bound water of these microaggregates. Kinetic data show that the electrophilicity of water, i.e. its hydrogen-bond donor ability, is increased by a fac tor of up to 65 as compared to bulk water. Within the bound-water phas e a gradient of counter-ion concentration is observed since the electr ophilicity increase depends on the probe location, close to the interf acial layer or to the micellar core. Product data give evidence for a change in the nucleophilic reactivity of this unusual water. These res ults are discussed in terms of new routes for biomimetic chemistry.