Oxidation in Three-Liquid-Phase Microemulsion Systems Using Balanced Catalytic Surfactants

A series of Balanced Catalytic Surfactants (BCS) [(C-n)(2)N(C-1)(2)](2)MoO4 (n = 8, 9, 10, 12) based on amphiphilic double-tailed quaternary ammonium with molybdate as a counterion has been developed for the dark singlet [4 + 2] cyclooxygenation of organic substrates in three-liquid-phase microemulsion systems. These cationic surfactants form three-liquid-phase microemulsion systems at room temperature in the presence of an appropriate organic solvent and water without addition of any cosurfactant or electrolyte. Comparative peroxidation of rubrene points out the speck advantages of these three-phase media over phase transfer catalysis in two phase systems and on conventional one-phase microemulsions based on sodium molybdate: (i) only three constituents, (ii) low amounts of surfactants, (iii) insensitivity to water dilution, (iv) fast separation of the three phases, (v) straightforward recovery of the product and the surfactant from the oil and microemulsion phases, respectively. The preparative peroxidation of a-terpinene and 1,4,5-trimethylnaphtalene was performed in the ternary systems [(C-8)(2)N(C-1)(2)](2)MoO4/water/tert-butyl acetate or benzene. The reusability of the catalyst, the catalytic nature of the BCS, and the ability of the systems to oxidize poorly reactive substrates were demonstrated showing the broadness of the applicability of such systems.