Study On Catalytic Synthesis Of Benzophenone Over Lewis Acidic Ionic Liquids

Benzophenone is important organic intermediates and additives for the production of fine chemicals, including organic coating, pharmaceutical, dyes, plastic, fragrances, agrochemical and other chemical industries. Traditionally, these reactions are carried out using Lewis acid and proton acid catalysts. Homogeneous catalysts have several disadvantages: corrosion, low selectivity, separation of the final product from the catalyst, difficulty in catalyst recovery, environmental pollution. To avoid these problems, solid acid catalysts have recently been as heterogeneous catalysts for these reactions. Still, solid acids have shortcomings as well. The more troublesome of these are very low conversion, rapid deactivation from coking, and rigorous reaction conditions. Hence, there are great realistic significance and economic valuation for the synthesis of benzophenone to develop efficient and environmental-friendly catalysts.Functionalized acidic ionic liquids have shown excellent catalytic activity and can be conveniently recycled as dual catalyst-solvent because of their tunable properties, non-volatile and homogeneous active sites. In this paper, the liquid phase acylation of benzene with benzoylchloride has been investigated using Lewis acidic ionic liquids. The experiment results indicated that the ionic liquid [Emim]Br/FeCl₃ have better catalytic activity and are separated from reaction products more easier. And this method features high yield in a short reaction time, a simple product isolation procedure, efficient and environmentally friendly synthesis route.At first, 11 kinds of Lewis acidic ionic liquids were synthesized by altering organic cation, inorganic anion and the molar fraction of MCly in ionic liquids. They include [Bmim]SbF₆, [Bmim]Cl/AlCl₃, Bmim]Cl/CuCl, [Bmim]Cl/FeCl₃, [Bmim]Cl/ZnCl₂, [Bmim]Cl/SnCl₂, [Emim]Br/AlCl₃, [Emim]Br/CuCl, [Emim]Br/FeCl₃, [Emim]Br/ZnCl₂, [Emim]Br/SnCl2. These samples were characterized by IR spectroscopy.Second, Acidic sites and the strength of acidity of acidic ionic liquids have been studied by IR technique using acetonitrile as a probe molecule. Third, Friedel-Crafts acylation of benzene with benzoylchloride to produce benzophenone was studied over various Lewis acidic ionic liquids as catalyst. Highest yield of benzoylchloride is obtained on the [EmimjBr/FeCl₃ . Effects of reaction temperature, reaction time, the amount of the acidic ionic liquid, the mole ratio of the reactants and the . molar fraction of FeCl₃ on yield of benzophenone were investigated. The optimized conditions were [Emim]Br/FeCl₃ 2.92g, the mole ratio Ben/BOC 3.0, the molar fraction of FeCl₃ 0.75 at 80℃reacting 80min. At above conditions, the yield of yield of benzophenone reached 96.3%.At last, the relationship between the acidity of acidic ionic liquids and the catalytic activity was investigated. At the same time, the possible Friedel-Crafts acylation reaction mechanism over [EmimJBr/FeCl₃ catalyst was discussed.