Epoxidation Of Olefins With Hydrogen Peroxide By A Monolacunary-keggin Type Heterpolyphosphotungstate

As one kind of important organic raw materials and intermediates, the epoxidesof olefins are widely used in the fields of petroleum, fine chemicals and organicsynthesis. Epoxidation of olefins with hydrogen peroxide by a Keggin typeheterpolyphosphotungstate, which is characterized by simple and feasible process,considered to be one very promising craft in industrial application without anyenvironmental pollution. Due to lacunary-Keggin type heterpolyphosphotungstate ismore likely to prouduce “active sites”, and has a better catalytic activity and stabilitycompared with saturated one. It has become a noteworthy direction in research ofolefin epoxidation.Firstly, several methods of preparing the monolacunary heterpolyphosp-hotungstic sodium Na7PW11O39were compared. By using imidazolium cation, whichare of different lengths of carbon chain(butyl, hexyl, decyl, myristyl and sixteen alkyl)to replace sodium ions, Q4Na3PW11O39and Q7PW11O39(Q: imidazolium cation ofdifferent lengths of carbon chain) were prepared. The samples were confirmed withmonolacunary-Keggin structure by FT-IR and31P NMR characterization. And in theprocess of contact with H2O2, the bond of W-Ob-W and W-Oc-W were broken,generating new reactive oxygen species [W(O2)]. It was unstable and gradullyconverted into W-Ob-W and W-Oc-W with the extention of time and consumption ofH2O2.Secondly, compared with saturated one, the catalytic performance ofmonolacunary-Keggin type heterpolyphosphotungstate of different lengths of carbonchain in reaction of cyclohexene epoxidation were investigated, with the oxidant ofH2O2and the solvent of acetonitrile. And at the same time, the structure of the catalystbefore and after reaction were characterized by the FT-IR and TG-DSC. The resultsshowed that: the monolancuncy Keggin-type heterpolyphosphotungstate gave a bettercatalytic performance than the saturated one, and the selectivity of cyclohexene oxidebased on cyclohexene was as high as99.02%, and the yield based on H2O2was92.66%; The length of carbon chain of imidazolium cation had no linear relationshipwith its solubility in the acetonitrile; and only the sixteen alkyl imidazole salt canprecipitate after reaction; the epoxy cyclohexane selectivity and the yield increasedwith decreases of catalyst solubility in acetonitrile; The structure of monolacunary-Keggin type heterpolyphosphotungstate was stable after reaction.Then the monolacunary-Keggin type heterpolyphosphotungstate was used inchloropropene epoxidation reaction system, and the effect of the reaction parameterson catalytic activity and the changes of structure after the reaction were investigated.The results showed that: when using1,2-dichloroethane as the solvent, addinghydrogen peroxide dropwise at50℃for4h, the monolacunary-Keggin typeheterpolyphosphotungstate gave a better catalytic performance. The H2O2conversionwas96.43%, the epoxy chloropropane selectivity and yield based on hydrogenperoxide were75.30%and72.61%, respectively. The result of catalyst recycleindicated that, the saturated-Keggin structure heterpolyphosphotungstate degradatedinto the lacunary one after reaction, but the monolacunary-Keggin structure was keptstable characterized by FT-IR.