Green Oxidation Of Isoeugenol Based On New Vanadium And Copper Catalysts

Vanillin is a ?avor with a dense of sweet cream odor. Since its structure was determined by Tiemann et al in 1874, vanillin has become one of the most important ?avors. The annual demand for vanillin is reported to be 15,000 tons. Due to the irrevocable decrease in fossil resources, the use of renewable isoeugenol to produce natural vanillin via green oxidation will be more and more impending. However, the intramolecular active C=C double bond and phenolic hydroxyl group of isoeugenol can result in such side reactions as epoxidation, rearrangement,hydration and deep oxidation, leading to the poor yield of vanillin.Vanadium and copper, usually important constituents of oxidation catalysts and the center elements of vanadium haloperoxidases or catechol oxidase as well, can utilize H2O2 for the selective oxidations under mild conditions. Herein, series of novel and highly efficient catalysts such as oxovanadium aromatic carboxylates, copper-containing metal organic frameworks, Cu2+-based ionic liquid were synthesized and applied to the catalytic oxidation of isoeugenol using aqueous H2O2 as the green oxidant. Goog results were obtained and the main contents of the thesis are summarized in the following:1. A series of oxovanadium 1,3,5-benzenetricarboxylate complex catalysts were prepared and characterized by FT-IR, diffuse reflectance UV-Vis(DR UV-Vis) and TG, respectively. The effects of reactionconditions on the oxidation of isoeugenol to vanillin were investigated systematically. It was found that complete conversion of isoeugenol and87.2% yield of vanillin can be achieved using VO(BTC)-1 as catalyst,1-dodecyl-3-methylimidazolium chloride([C12mim]Cl) as additive when isoeugenol: H2O2: [C12mim]Cl =1: 2: 0.01(mole ratio) after 24 h reaction at 20 ℃ in acetone. This is due to the formation of a highly effective oxidation system from [C12mim]Cl/VO(BTC)-1 and H2O2 that is beneficial in the mild conversion of isoeugenol, as supported by spectral characterization and reaction results.2. Prefabricated Cu2+-based ionic liquid catalysts and[Hmim]HSO4-CuCl2 were examined for the oxidation of isoeugenol. The in-situ-formed [Hmim]HSO4-CuCl2 was verified by UV-Vis spectra. The optimum reaction conditions were as follows:(1) using prefabricated Cu2+-based ionic liquid as catalyst, acetonitrile-water as solvent, 30%aqueous H2O2 as oxidant after 3 h reaction at 25℃, the selectivity and yield of vanillin were 79.3% and 49.6%, respectively;(2) using in-situ prepared CuCl2-[Hmim]HSO4([Hmim]HSO4 : CuCl2 =1 : 1(mole ratio))as catalyst, acetonitrile as solvent, 30% aqueous H2O2 as oxidant after 7 h reaction at 30℃, the selectivity and yield of vanillin were 84.1% and61.9%, respectively.3. A series of micro/nanoscale CuMOFs were prepared from1,3,5-benzenetricarboxylate ligand and their structure was characterizedby FT-IR, TG and TEM, respectively. The influence of reaction conditions on the oxidation of isoeugenol was studied. The optimum reaction conditions were as follows: using CuBTC-1 as catalyst,acetonitrile as solvent, 30% H2O2 as oxidant after 8 h reaction at 50℃,86.7% selectivity and 81.9% yield of vanillin can be obtained.Additionally, micro/nanoscale CuBTC-1 catalyst can be used repeatedly.