Self-assembly of reverse micelle nanoreactors by zwitterionic polyoxometalate-based surfactants for high selective production ofβ-hydroxyl peroxides

Surfactants with polyoxometalates(POMs)as polar head groups have shown fascinating self-assembly behaviors and various functional applications.However,self-assembly them into reverse micelles is still challenging owing to the large molecular size and intermolecular strong electrostatic repulsions of POM heads.In this work,a zwitterionic POM-based surfactant was synthesized by covalently grafting two cationic long alkyl tails onto the lacunary site of[PW_(11)O_(39)]^(7-).With decreased electrostatic repulsions and increased hydrophobic effect,the POM-based reverse micelles with an average diameter of 5 nm were obtained.Interestingly,when these reverse micelles were applied for catalyzing the oxidation of styrene,an unprecedentedβ-hydroxyl peroxide compound of 2-hydroxyl-2-phenylethan-1-tert-butylperoxide was produced in high selectivity of 95.2%.In comparison,the cetyltrimethylammonium electrostatically encapsulated POMs mainly generated the epoxides or 1,2-diols.A free radical mechanism was proposed for the oxidation reaction catalyzed by the zwitterionic POM surfactants.