The Selective Oxidations Of Sulfides To Sulfoxides And Alkynes To α,β-Acetylenic Ketones And In Polyethylene Glycol

With increasing concern on the environmental protection, the development of environmentally benign catalytic systems has received great concerns. To improve reaction efficiency and selectivity, reduce the use of toxic organic solvent and avoid pollution, this dissertation is mainly focused on employing green oxidative system for organic synthesis.As reaction media, organic solvents are widely applied to conventional organic synthesis. As alternative solvents, water, room temperature ionic liquids, immobilized solvent and supercritical fluids have been used for green organic synthesis. Because of the unique solvent properties, supercritical carbon dioxide (scCO2) has wide applications in extraction, chromatography and so forth. With respect to oxidative reactions, scCO2has many advantages when compared to conventional organic solvents, including chemical inertness, excellent miscibility with dioxygen and reaction substrates, easy separation and so on. Polyethylene glycol (PEG) and its derivatives are commonly known to be inexpensive, non-toxic, nearly non-volatile, thermally stable, and environmentally benign media for chemical reactions and phase transfer catalysts. In addition, PEGs have good affinities with carbon dioxide. Combining with scCO2which is also a green solvent, the generated biphasic system will reveal remarkable solvent properties.a,(3-acetylenic ketones are extremely versatile intermediates for the preparation of various biological heterocyclic compounds. This dissertation studied PEG radical initiated oxidation of alkynes with dioxygen to corresponding α,β-acetylenic ketones. The tunable solvent properties of compressed carbon dioxide render the control of reaction selectivities possible. The experimental results indicated that the desired product was obtained in excellent yield and selectivity. Additionally, the synthetic steps were reduced and the organic oxidants and metal catalysts could be avoided. Based on the experimental results, we proposed that the reaction mechanism could be elucidated by an oxidative pathway involving PEG radical.Organic sulfoxides have wide applications in the synthesis of chemically useful and biologically active molecules such as drugs, flavors, germicides and catabolism regulators. According to previous reports regarding that liquid PEGs can immobilize and stabilize the in situ formed metal intermediate, we design and implement a highly efficient process for the selective synthesis of sulfoxides through the Fe(acac)2-catalyzed aerobic oxidation of sulfides with dioxygen as an oxidant in PEG1000. Comparing with conventional methods, this process avoids the use of toxic organic solvent, noble metal catalysts and complex ligands. A catalytic mechanism involving iron-oxo species was proposed. PEG could play an essential role in stabilizing the iron-oxo species, which are responsible for oxygen transfer to sulfides, through non-covalent interactions. NMR and HRMS characterization was employed to try to get some evidence for the proposed mechanism.