Selective Molecular Oxygenation Of Cumene Catalyzed By NHPI To Cumyl Hydroperoxide

Cumyl hydroperoxide is an important chemical intermediate.Industrially,it is manufacturated by cumene autooxidation using a small amount of cumyl hydroperoxide as initiator predominantly under a reaction temperature 110-115℃ and an air pressure of 0.4-0.6 MPa.However,it is found that the industrial production conditions are harsh with a low yield.From the perspective of green chemistry,it is urgent to develop an efficient catalytic system and realize the preparation of the target product cumyl hydroperoxide through the oxidation reaction of C-H bond of cumene at room temperature and atmospheric pressure.In this thesis,different solvents were firstly modulated for selective cumene oxidation catalyzed by homogeneous NHPI/Co via dioxygen,and the possible reaction network and reaction mechanism of cumene oxidation were investigated using homogeneous Co and NHPI as the catalyst.Then,the influence of different phase transfer catalysts on the catalytic oxidation performance of cumene via dioxygen catalyzed by homogeneous NHPI/Co was researched in acetonitrile,and the possible reaction mechanism of cumene to cumyl hydroperoxide was studied using homogeneous NHPI/Co/DDAB as the catalyst.Finally,the performance of different homogeneous metal ions（Cu（Ⅱ）,Co（Ⅱ）,Mn（Ⅱ）,Fe（Ⅱ））or its supportd catalyst MOx/SiO2（M=Cu,Co,Mn,Fe）was also compared for oxidation of cumene synergistically with NHPI.The properties such as composition,structure,morphology and chemical state of the multiphase catalysts were characterized to investigate the conformational relationships of the catalysts.The prepared copper oxide catalyst and NHPI were used in the synergistic catalytic selective oxidation reaction of cumene via molecular oxygen to test the activity and stability of the catalyst under the reaction conditions.Meanwhile,the mechanism of selective oxidation of cumene was investigated which was initiated by homogeneous or heterogeneous catalysts.（1）Effect of solvents on aerobic oxidation of cumene to cumyl hydroperoxideThe effects of different solvents on the selective oxidation of cumene to cumyl hydroperoxide using dioxygen in liquid phase were compared at room temperature.Compared with benzyl benzoate,benzonitrile and acetic acid,hexafluoroisopropanol significantly promoted the conversion of cumene to cumyl hydroperoxide at ambient temperature and pressure.Under the optimal reaction conditions,the conversion rate of cumene and selectivity of cumyl hydroperoxide were up to 64.3%and 71.7%,respectively.The solvent hexafluoroisopropanol significantly increased the concentration of PINO radical and promoted the conversion of cumene to the target product cumyl hydroperoxide.In addition,the presence of the cumyl radical was captured successfully by TEMPO and analyzed by HRMS.In the reaction mixture,the existence of PINO free radicals and cumyl radicals indicated that the oxidation reaction of cumene catalyzed by Co and NHPI may follow a radical mechanism.NHPI was activated by cobalt oxygen free radicals at the chain initiation stage to generate PINO free radicals,which H-abstract the benzylic C-H bonds to generat the carbon free radicals.They reacted with molecular oxygen to further generate cumyl peroxy radicals,which abstracted hydrogen atom from NHPI to produce the desired CHP and realized the regeneration PINO radicals.（2）Aerobic oxidation of cumene to cumyl hydroperoxide promoted by phase transfer catalystBecause hexafluoroisopropanol is expensive,in order to reduce the reaction cost and improve the reaction activity,the method of changing the solvent and adding phase transfer catalyst in the reaction system to obtain high yield of cumyl hydroperoxide.By comparing the effects of different phase transfer catalysts on the catalytic oxidation reactivity of cumene via molecular oxygen catalyzed by NHPI/Co,it was shown that adding appropriate amount of phase transfer catalysts into the cumene oxidation system can improve the catalytic activity of NHPI,and the main product is cumyl hydroperoxide.Compared with dodecyl dimethyl betaine（BS-12）,octyl phenol polyoxyethylene ether-10（OP-10）,sodium dodecyl sulfate（SDS）and cetyl trimethyl ammonium bromide（CTAB）,didodecyldimethylammonium bromide（DDAB）had a significant promoting effect on the oxidation of cumene catalyzed by NHPI/Co.Under the optimal reaction conditions,the conversion rate of cumene and the selectivity of the target product cumyl hydroperoxide can reach to 99.5%and 83.5%,respectively.At the same time,the possible mechanism of DDAB in the catalytic oxidation of cumene via molecular oxygen catalyzed by NHPI/Co was also discussed through catalytic test and optical microscope observation.The excellent activity may be attributed to the ability of DDAB to self-assemble into reverse multilayer vesicles in the oxidation of cumene using acetonitrile as solvent.Under the reaction condition,the vesicles acted as microreactors,in which NHPI/Co and cumene can be accumulated.DDAB on the bilayer can extract Co into the organic phase,and form intermolecular hydrogen bond with NHPI,so that cumene and NHPI/Co can get full contact and reaction at the membrane interface,and improved the conversion rate of cumene.DDAB significantly increased the concentration of PINO in the reaction solution catalyzed by NHPI/Co in acetonitrile,and promoted the conversion of cumene to the product cumene hydroperoxide.The cumly radical and cumyl peroxy radical were successfully captured by free radical spin trapping agent DMPO and analyzed by EPR.In addition,the presence of cumyl radical was captured and observed with radical trapping agents TEMPO and HRMS,respectively.The presence of PINO free radical and cumyl radical in the reaction solution indicated that NHPI/Co/DDAB catalyzed cumene oxidation may follow a similar reaction mechanism as NHPI/Co catalyzed cumene oxidation in hexafluoroisopropanol.（3）Effect of transition metal ions on aerobic oxidation of cumene to cumyl hydroperoxide and theirs fixationDifferent homogeneous metal ions（Cu（Ⅱ）,Co（Ⅱ）,Mn（Ⅱ）,Fe（Ⅱ））or their supported catalysts MOx/SiO2（M=Cu,Co,Mn,Fe）and NHPI were used as synergistic catalysts for the oxidation of cumene,and the effects of different metal ions on the reaction were investigated.The results showed that Cu（Ⅱ）has the best synergism with NHPI for cumene oxidation.The prepared CuOx/SiO2 catalyst was mainly composed of monocline copper oxide（CuO）which was highly dispersed,and exhibited good textural properties.Under the optimized experimental conditions,the conversion rate of cumene and the selectivity of cumyl hydroperoxide were up to 100%and 82.5%,respectively.The main byproducts were acetophenone and 2-phenyl-2-propanol.The performance of the recycled catalyst did not decrease obviously and showed good reusable capability.The excellent catalytic performance,stable recyclability and good texture indicated that the prepared CuOx/SiO2 had the prospect of industrial application.PINO free radical and cumyl radical were observed by EPR and HRMS,respectively,in the reaction solution catalyzed by homogeneous or heterogeneous catalysts.The catalytic test and characterization results showed that supported copper oxide catalyst can initiate the oxidation of cumene to cumyl hydroperoxide as homogeneous Cu（OAc）2,and the reaction may follow the free radical mechanism.In conclusion,solvent was found a great influence on the selective molecular aerobic oxidation reaction of cumene catalyzed by NHPI/Co.Hexafluoroisopropanol significantly increased the concentration of PINO radical in the reaction mixture,and thus increased the conversion rate of cumene to cumyl hydroperoxide.DDAB can self-assemble into reverse multilayer vesicles in the catalytic oxidation reaction of cumene with molecular oxygen catalyzed by homogeneous NHPI/Co.The vesicles formed are thought to have the function of microreactor under the reaction conditions,which can aggregate cumene and NHPI/Co in the reactor.Co can be extracted into the organic phase by DDAB,and NHPI can form intermolecular hydrogen bond with DDAB on the bilayer,so that cumene and NHPI/Co are fully contacted and react at the membrane interface,thus improving the catalytic activity of NHPI/Co in the oxidation reaction of cumene.Cu（Ⅱ）and NHPI showed excellent catalytic performance in the liquid phase selective oxidation of cumene.Copper oxide catalysts were found to have good textural properties and structural stability,and can be recycled.The oxidation reaction of cumene initiated by heterogeneous copper oxide or homogeneous copper catalyst may follow a free radical mechanism.