3,5-difluorobenzophenone

Preparation

Synthesis of 3,5-Difluorobenzophenone: Prior to acylations, 3,5-difluorobenzoic acid was reacted with freshly distilled thionyl chloride and catalytic amounts of DMF(2 drops). After two hours at 55 °C, the excess thionyl chloride was distilled between 75 and 77 °C. The acid halide was then fractionally distilled at 174 °C, and recovery was generally around 75%. To a 50 mL round bottom flask, equipped with a gas inlet, addition funnel, condenser, and drying tube, were added 3.01 g (22.6 mmol) of AlCl3. A mixture of 3.62 g (20.5 mmol) 3,5-difluorobenzoyl chloride and 8.01 g (102.5 mmol) benzene was added dropwise to the AlCl3. The reaction mixture was stirred for 4 hours, before heating to 75 °C. After 16 hours the reaction mixture was quenched by pouring into acidic ice water, followed by addition of 300 mL of chloroform, and transferring to a separatory funnel. The layers were separated and the organic layer was washed with 5 wt. % bicarbonate, distilled water, and then dried with MgSO4 and the solvents were removed, via rotary evaporation, leaving an off-white solid. The crude material was recrystallized from aqueous ethanol to afford (3.00 g, 67 %) of a crystalline white solid with a m.p. 58-59 °C (lit.21 m.p. 57-58 °C); 1H NMR (300 MHz, CDCl3, δ) 7.04 (tt, 1H, J = 8.4, 2.4 Hz), 7.31 (m, 2H), 7.51 (m, 2H), 7.63 (tt, 1H, J = 7.5, 1.2 Hz), 7.78 (m, 2H)