Greening Processes For The Preparation Of Benzophenone

Friedel-Crafts benzoylation of arenes lead to benzophenones, which are important intermediates in a very wide field of chemistry, including pharmaclolgicals, dyes, fragrances and agrochemical, such as fungicides, herbicides and insecticides. Many of the industical processes still use HF or AlCl3 as catalyst for this kind of reaction, producing a high amount of contaminated waste, increasingly demanding environmental pressure and the resulting drive towards clean technologies force us to developing ecologically friendly alternatives.An ionic liquid is a liquid that consists entirely of ions and possess a very wide liquid range, negligible vapor pressure, excellent thermal and chemical stability, the weaker coordination, tunable acidity, basicity and miscibility in a variety of solvents. Recently, ionic liquids get a wide application in organic synthesis as either solvents or catalysts.In our recent research, the liquid phase benzoylation of benzene with benzoyl chloride has been investigated using Et₃NHCl-FeCl₃ ionic liquid as catalyst. The experimental results indicated that the ionic liquid displayed an excellent catalytic performance and the ionic liquid catalyst may be a promising and friendly environmental industrial catalyst for the synthesis of benzophenone. The influencing factors on the benzoylation of benzene were discussed in details and the yield of 80.7% for benzophenone was attained under the optimized reaction conditions.At the same time, we also wish to report for the first time, a novel catalytic system for the direct synthesis of benzophenone from benzotrichloride, benzoic acid and benzene using Et₃NHCl-FeCl₃ ionic liquid as catalyst, which has not been reported so far. The inherent atom economy of this process is 76.91%, which is much higher than that(62.84%) of the accustomed process, and the experimental results also showed that the ionic liquid Et₃NHCl-FeCl₃ is an excellent catalyst for the direct synthesis of benzophenone from benzotrichloride, benzoic acid and benzene due to its higher yield, and which can be reusable and functions as a true catalyst in the reaction. It builds anaccess to the synthesis of benzophenones by an excellent and green catalyst in the future.