Study On Catalytic Oxo-functionalization Of Cumene To High Value-added Oxygen-containing Compounds

Oxygen-functional products of cumene,such as cumene hydroperoxide,acetophenone,and 2-phenyl-2-propanol,are crucial raw materials in chemical production.In traditional industry,a small amount of cumene hydroperoxide is utilized as an initiator to catalyze the self-oxidation reaction of cumene under harsh conditions,with an air pressure of 0.4-0.6 MPa and a reaction temperature of 110-150℃.However,this method suffers from low substrate conversions,poor safety,excessive byproducts,and strict reaction conditions.Therefore,it is imperative to develop an efficient method for cumene oxygen functionalization that can proceed under milder reaction conditions with higher selectivities for high-value-added products.In this dissertation,we investigate the immobilization of nitrogen-oxygen free radical catalysts and their initiator Co2+on solid supports,and characterize the composition,morphology,structure,and elemental chemical state of the prepared heterogeneous catalyst.Explored were the factors that affect the oxygen functionalization of cumene under solvent-free conditions after optimizing reaction conditions.Accordingly,We evaluated the activity and stability of the catalysts fabriated.and investigated the catalytic reaction mechanism for the oxygen functionalization of cumene.1.Synthesis of nitrogen-oxygen free radical catalysts via copolymerization and their catalytic performance in cumene oxygen functionalizationThe St-NHMI catalyst,synthesized via high-molecular-weight polymerization of styrene-N-hydroxymaleimide,was used to perform cumene oxygen functionalization reactions.The activity of the resulting catalysts was compared under different styrene/maleic anhydride feed ratios.The reaction was carried out in acetonitrile solvent using a St-NHMI/Co(Ⅱ)heterogeneous catalyst.The catalyst St-NHMI-1.5,prepared under a styrene/maleic anhydride feed ratio of 1:1.5,exhibited the highest activity for cumene oxidation.After optimizing the reaction conditions,this catalyst system demonstrated excellent activity and stability,with a cumene conversion of 93.3%.The selectivities to acetophenone,2-phenyl-2-propanol,and cumene hydroperoxide were 79.2%,13.5%,and 7.2%,respectively.Nitrogen-oxygen free radicals were observed by EPR under reaction conditions,indicating that the reaction may proceed through a free radical mechanism.Based on the distribution of oxygenated products in cumene oxygen functionalization and control experiments,a reaction network for cumene oxygen functionalization was established,and a reaction mechanism was proposed.Co2+forms a cobalt complex intermediate with O2,which activates NHMI to generate MINO free radicals.The carbon free radical generated by capturing the hydrogen atom on the benzyl C-H bond further reacts with molecular oxygen to form a peroxy free radical,achieving chain growth.2.NHPI/Co catalyzed solvent-free oxygen functionalization of cumene and the effect of phase transfer catalyst on the reactionExplored were the factors influencing the solvent-free oxidation of cumene catalyzed by NHPI/Co,with the role of phase transfer catalysts in the reaction investigated.Experimental results revealed that the addition of phase transfer catalysts significantly promoted the progress of the reaction.Five different types of phase transfer catalysts were tested,and dodecyl dimethyl bromide ammonium(DDAB),a cationic surfactant,was found to possess the best synergistic role with the NHPI/Co catalytic system.This study suggested that DDAB could form intermolecular hydrogen bonds with NHPI,allowing NHPI to dissolve in organic media and extract Co into the organic phase,thereby enhancing the solubility of the catalyst and the contact between the substrate and the catalyst,thus promoting the reaction.Under optimal conditions,this method converted 84.9%of CM into products,with a CHP selectivity of 83.2%.The study also employed EPR to detect the presence of PINO radicals and captured and detected quinone radicals using TEMPO and high-resolution mass spectrometry,proving that the reaction followed a free radical mechanism.3.Co-immobilization of NHPI/Co and its solvent-free cumene oxygenfunctionalization performanceNHPI and its initiator Co2+were co-immobilized on the carrier SiO2 to prepare the co-immobilized catalyst CoOx/SiO2-APTES-PMDA-NOH.The compositions,structure,and properties of the catalyst were studied by elemental analysis,FT-IR,XRD,XPS,and other methods.The Fourier transform infrared spectroscopy of the catalyst showed the formation of the O=C-N-C=O amide grafting bond,indicating that NHPI was successfully grafted onto the carrier.The synthesized co-immobilized catalyst CoOx/SiO2-APTES-PMDA-NOH,immobilized catalyst SiO2-APTES-PMDA-NOH,homogeneous Co(acac)2,immobilized cobalt Schiff base catalyst SiO2-APTES-SA-Co,homogeneous NHPI,and immobilized NHPI catalyst were compared with the immobilized cobalt schiff base catalyst in a mechanically mixed solvent-free condition.The results showed that the co-immobilized CoOx/SiO2-APTES-PMDA-NOH had the highest cumene oxidation activity,with cumene conversion rate and CHP selectivity reaching 77.9%and 66.5%,respectively.The cyclic tests of the synthesized catalyst showed an excellent activity stability of the co-immobilized catalyst CoOx/SiO2APTES-PMDA-NOH.In summary,nitrogen-oxygen free radical catalysts(NMHI,NHPI,and/or Co2+initiators)were successfully immobilized onto the supports using copolymerization or grafting methods,and extensive research on the composition,structure,and properties were performed to investigate the synthesized heterogeneous catalysts St-NHMI and CoOx/SiO2-APTES-PMDA-NOH.The catalysts exhibited high-density active sites and excellent catalytic performance for the oxygenation reaction of cumene.We also investigated the activity of the catalysts in the cumene oxygenation reaction under solvent-free conditions and found that the addition of a phase transfer catalyst promoted the reaction,among which the cationic surfactant DDAB exhibits the best synergistic performance with the catalyst.The co-immobilized catalyst CoOx/SiO2-APTESPMDA-NOH showed the highest catalytic activity and excellent stability,indicating its potential for industrial applications in the selective oxidation of cumene to produce hydrogen peroxide using a fixed-bed flow reactor.