Design Of Catalyst With Controllable Phase Transfer Capability For Catalytic Oxidation In Water

With the increasing attention of environmental issues,green catalytic process,especially aqueous catalysis,has drawn much attention in the field of intermational catalysis.VWhile limited by the mass transfer,traditional catalysts are often less efficient in aqueous organic reaction.Herein,a series of lewis acid catalysts with controlled phase transfer capability was designed for aqueous catalysis.The catalysts were high efficient in aqueous reaction due to build-in phase transfer ability,and could be facile recovered for reuse.Thus,the problems associated with the phase-transfer limitation in the biphasic reaction and the separation of the catalysts can be well resolved.Given that polyethylene glycol(PGE)has excellent phase transfer ability,a PEG-bridged gemini imidazole ionic liquid was designed and used to couple the Keggin-type phosphotLngstic acid anion(PW12O4O3-,PW12)by ion exchange.The obtained PW-based catalysts were insoluble in the aqueous phase,but form water soluble active species by the action of H2O2;when H2O2 is used up,the catalyst precipitates again from the aqueous phase.This unique solubility allowed the PW-based catalysts to undergo reaction-controlled phase transfer catalysis in oxidation of alcohols with aqueous H2O2 in water,exhibiting high efficiency and facile reusability for the aqueous catalysis.Based on the thermo sensitivity of poly N-isopropylacry lam ide(PNIPAAm),a novel thermoresponsive surfactant-type chiral salen rMn(?)catalyst was developed by covalently grafting "smart"poly(N-isopropylacrylamide)(PNIPAAm)onto a neat chiral salen Mn(?)complex.Characterization data suggests thermoresponsive micellization behavior of the obtained catalyst in water.The chiral catalysts could self-assemble to form a nanoreactor in the asymmetric epoxidation of unfunctionalized olefins in water,dramatically accelerating the aqueous epoxidation.Moreover,they could be easily recovered by thermocontrolned separation and reused for several times without loss of activity.Given the thermo sensitivity of PNIPAAm,SnC14-based Lewis acid ionic liquid(BL)was copolymerized with NIPAAm monomer through radical polymerization.The obtained thermoresponsive,amphiphilic copolyier exhibited thermoresponsive micellization behavior in water.At room temperature,it self-assembled through intermolecular hydrophobic effect,foraning water-soluble micelle with SnCl4-based IL core and PNIPAAm shell.The metallomicelle behaved as a nanoreactor,accelerating Baeyer-villiger oxidation of cyclobutanone with aqueous H2O2(30 wt.%)in water.After the reaction,the catalyst could be facilely separated for reuse by adjusting the local temperature up to its LCST.