Balanced catalytic surfactants

Multiphase Microemulsions with Balanced Catalytic Surfactants... 

II system). The WI system is particularlyrelevant with regard to the ease of workup since the product is extracted into the excess oil phase and the catalyst remains in the microemulsion phase. However, it is still sensitive to dilution by water arising from H2O2 disproportionation. This can be avoided by using pervaporation membrane [71]. A further improvement has been brought by three-hquid phase microemulsion systems based on balanced catalytic surfactants [72]. This new kind of catalysts is carefully designed in order to provide spontaneously a Winsor... 

III microemulsion system in the presence of water and an appropriate oil, without requiring cosurfactant nor electrolyte. They play a dual role as [1] Oj generating catalyst and as surfactant stabilizing the bicontinuous microemulsion. From a physicochemical point of view, they must have an effective packing parameter close to one [73]. Bis(dimethyldialkylammonium)molybdates are typical examples of such balanced catalytic surfactants, which lead to a three-phase system as shown in Figure 22.6. In such reaction media, 02 is exclusively generated in the aqueous nanodomains of the middle-phase microemulsion where the reaction takes place. Under stirring, the excess oil phase transfers the substrate S to the... 

Figure 22.6 Three-liquid phase microemulsion (Win-sor III] based on the balanced catalytic surfactant bis(dimethyldioctylammonium)molybdate.

DSO via molybdate-catalyzed disproportionation of HjOj provides a readily scalable alternative to photooxidation. It can be carried out in commonly available stirred-tank reactors. However, the reaction does not work at low temperatures and organic media are limitedto alcoholic polar solvents (methanol or the safer ethylene glycol) or to microstructured media such as one-, two-, or three-phase microemulsion systems. The latter based on balanced catalytic surfactants advantageously combine low surfactant concentration with easy product isolation and catalyst recycling via simple phase separation. Safe processing may be further enhanced by microreactors, which minimize peroxide hold-up. 

Rataj VN, Caron L, Borde C, and Aubry JM. (2008). Oxidation in three lipid phase microemulsion systems using balanced catalytic surfactants. Journal of American Chemical Society, 130, 14914-14915. 

---