Design, Synthesis And Application In Oxidation Reaction Of Transition Metallate Functionalized Ionic Liquids

In this thesis, several transition metallate and (or) metal complex functionalized ILs were synthesized and used as the catalysts for selective oxidations of organic compounds with H2O2or O2as the oxidant; Based on the requirements for the additives in the specific catalytic oxidations, different functional groups such as-SO3H,-COOH,-NEt2, TEMPO etc., were also grafted into the IL to afford the functionalized-IL additives; In addition, the room temperature ILs were chosen as solvents due to the cleanness, good dissolving ability, and recyclability. Due to the structural similarity, the resultant metallate-(or metal complex-) functionalized ILs, additives-functionalzied ILs and room temperature ILs were mixed together to yield the compatible IL compositions (ILC), in which the green homogeneous oxidation of organic compounds were carried out effectively with advantages of cleanness and recyclability.In our work, four types of functionalized ILC systems were synthesized for the catalytic oxidations of organic compounds.(1) The ILC containing phosphotungstate-functionalized IL as the catalyst for green homogeneous epoxidation of alkenes by aqueous hydrogen peroxide Scheme1The ILC for epoxidation of alkenes by H2O2 In order to realize epoxidation of lipophilic alkenes by hydrogen peroxide with excellent conversion and selectivity, α-Keggin type phosphotungstate functionalized IL was synthesized as a catalyst (1, Scheme1). Because alkenes were hydrophobic and hydrogen peroxide was hydrophilic, the IL mixtures of [Bpy]BF4and [Dopy]BF4were used as the amphipathic solvents to guarantee the homogeneous catalysis. The homogeneous oxidation of alkenes by aqueous hydrogen peroxide proceeded effectively in the ILC composed of catalyst1,[Bpy]BF4and [Dopy]BF4. It was found that the non-volatile ILC could be reused for6runs at least without significant loss of activity.(2) The ILC composed of'vanadate-acid-TEMPO'functionalized ILs for alcohol oxidation by hydrogen peroxide Scheme2The ILC for oxidation of alcohols by H2O2In order to realize the selective oxidation of alcohols to aldehydes or ketones by aqueous hydrogen peroxide, vanadate-functionalized IL (1) was synthesized as a catalyst firstly. Because the acid and the nitroxyl radical of2,2,6,6-tetramethylpiperidinyloxy (TEMPO) were pronounced to promote the activity and selectivity for the corresponding transition-metal-based catalysts, sulfoacid (-SO3H) and TEMPO were also incorporated into the ILs to afford sulfoacid functionalized IL (2) and TEMPO functionalized IL (5).1,2and5were dissolved in room temperature [Bpy]BF4to yield the'cock-tail'like multi-functional ILC, in which the catalytic performance of1was dramatically improved due to the synergetic effect coming from2and5(Scheme2). The non-volatile ILC composed of1,2,5and [Bpy]BF4could be reused for6runs without obvious activity loss.(3) The ILC containing'sulfoacid (SO3H)-hexafluorotitanate (TiF62-)' bi-functionalized IL as the catalyst for selective sulfoxidation of sulfides to sulfoxides by hydrogen peroxideScheme3The ILC for sulfoxidation of sulfides by H2O2In order to carry out green sulfoxidation of sulfides to sulifoxides by aqueous hydrogen peroxide under mild conditions, the bi-functionalized IL of1containing sulfoacid and hexafluorotitanate was synthesized and used the catalyst.1with the use of [Bpy]BF4as solvent could catalyze the sulfoxidation of sulfides to sulfoxide selectively under room temperature (Scheme3). The non-volatile ILC composed of1and [Bpy]BF4could be reused for6runs without obvious activity loss.(4) The ILC containing'Ru complex-phosphotungstate'bi-functionalized IL as the catalyst for selective oxidation of alcohols by molecular oxygen Scheme4The ILC for oxidation of alcohols by O2In order to improve the tolerance to oxidation degradation of the ruthenium complexes in aerobic oxidations, a novel bi-functionalized IL containing the cationic ruthenium complex and anionic phosphotungstate (2) was synthesized for the first time (Scheme4).2was featured with paramagnetism and insensitivity to oxygen and moisture. The stability of2was improved greatly due to the presence of phosphotungstate as the counter-anion. The ILC composed of2and [Bpy]BF4exhibited remarkable catalytic activity and could be recycled at least5runs without obvious activity loss for the aerobic oxidations of alcohols free of any additives such as base and nitroxyl radical. It was found that water could boost the activity of2significantly, probably due to its role in giving rise to the generation of RuⅣ=O species, which can be oxidized easily to the active O=RuⅥ=O by O2.