Studies On Green Oxidations And Related Tandem Reactions Based On Vanadium Catalysts

Oxidation is one of the most important types of reactions in the production of fine chemicals. However, due to the use of stoichiometric amount of heavy metal catalysts and the difficulties in the control of oxidation, oxidative process has also become an important factor leading to environment pollution. H2O2 and molecular oxygen are ideal oxidants since water is the sole by-product after utilization. Hence, it will be of great value both in science and applications for the exploration of green catalytic oxidations with high efficiency and selectivity using H2O2 and molecular oxygen as oxidants.Vanadium, an important and common composition in oxidation catalysts and the center element of vanadium haloperoxidases as well, can utilize H2O2 or molecular oxygen for the selective oxidations under mild conditions. Also, vanadium is a potential bi-functional redox-Lewis acid catalyst owing to the low radius and strong Lewis acidity of high valent V5+.This thesis focuses on the design of vanadium-based characteristic green oxidations and related tandem transformations with H2O2 and molecular oxygen as green oxidants. Analytic techniques such as 1H NMR、13C NMR、UV-Vis、FT-IR、GC-MS、XRD、ICP and density functional theory (DFT) methods were used in the investigation. Using anethole, isoeugenol, a-pinene and ethyl lactate that come from renewable resources, or styrene, tetralin and acetylacetone as model molecules, the selective oxidations of C=C bonds, allylic oxidation, oxidative dehydrogeneration and green tandem transformations were systematically studied by various homogeneous and heterogeneous vanadium catalysts. A series of excellent results were obtained. First, the characteristic and green catalytic oxidation systems based on vanadium catalysts were created. Second, multicarbonyl compound of new structure was selectively synthesized. In addition, the multifunctional catalysis and biomimic chemistry of vanadium catalysts were developed. The main contents of the thesis are summarized in the following:(1) Based on the special functions of aromatic carboxylic acids in stabilizing H2O2 and improving the efficiency of H2O2 in olefin oxidation, a series of oxovanadium aromatic carboxylates were synthesized and applied in the catalytic oxidation of anethole under mild conditions. The influences of ligands, media and time on the results were investigated and the optimal conditions were obtained. Experimental results indicated that multipurpose molecule DMF, which can be used both as a ligand and a pH modifier, would smartly tune the catalytic performance of oxovanadium aromatic carboxylates. Thus, it will provide a novel path for the design of oxovanadium complexes exhibiting high efficiency and selectivity. When the substrate was completely converted, a high selectivity 90% of product was obtained. Moreover, the efficiency of H2O2 utilization was very high. The reaction mechanism was explored by UV-Vis and FT-IR spectra.(2) The disodium phthalate-doped vanadium catalysts were prepared from V2O5 with glycerol as a reductant. The doped vanadium compounds were used to catalyze the oxidation of isoeugenol with H2O2.87.3% conversion of substrate and 89.4% selectivity for vanillin were achieved in CH3COCH3-DMF (20% v/v) under the conditions of 20℃, 4 h and isoeugenol:H2O2=1:2 (mol/mol).(3) The selective oxidation of styrene to benzaldehyde by H2O2 was investigated over V/ACO (oxygenated activated carbon) prepared from solid-state microwave irradiation. Results of experiments showed that the modification methods and loading conditions of support have significant influence on the conversion of styrene. The optimal performance, viz.87.2% selectivity for benzaldehyde at the complete conversion of substrate was provided by V-30%/ACO-1 which obtained from microwave irradiation using 50% H2O2-modified activated carbon. The catalyst could be repeatedly used for three times without remarkable loss of activity.(4) One-step conversion of a-pinene to campholenic aldehyde via VO(acac)2-catalyzed oxidation was explored under mild conditions. The eco-friendly transformation of renewable and abundant a-pinene is of great value both to economy and society. Reacting for 6 h in acetone at 20℃, conversion of a-pinene can reach up to 73.0% and selectivity of major products campholenic aldehyde and verbenone were 47.2% and 13.2%, respectively.(5) The allylic oxidation of tetralin to a-tetralone was thoroughly investigated over V2O5-H2O2. The selectivity of a-tetralone is as high as 92.5% at 28.5% conversion of tetralin under the conditions of tetralin:H2O2=1:2 (mol/mol),40℃and 24 h. The main characteristics of the process are as follows:simple operation, mild conditions and with high selectivity. The industrial use of the process will be possible when the conversion is further elevated.(6) A series of oxovanadium complexes of 8-hydroxyquinoline and its derivatives were prepared and applied in the tandem cleavage-addition-oxidative dehydrogeneration transformation of acetylacetone by molecular oxygen under mild conditions. And a multicarbonyl compound of new structure was selectively synthesized. Reacting for 24 h at 80℃, the conversion of acetylacetone is 60.6% and the yield of the objective product is 53.5%. The catalytic cycle is proposed to proceed via the formation of a synergetic free radical, which is supported by DFT calculations.(7) A series of heterogeneous oxovanadium catalysts VOSO4/ACO (VO/ACO) were prepared from oxygenated activated carbons (ACO) with high surface area. The catalytic performances of VO/ACO catalysts on the oxidation of ethyl lactate to ethyl pyruvate with molecular oxygen were investigated.95.2% selectivity for ethyl pyruvate and complete conversion of ethyl lactate were achieved under the conditions of 80℃and atmospheric pressure. The catalyst could be repeatedly used after proper disposal.