To an assembly of 2-liter 3 necked round bottom flask containing a mechanical stirrer, thermometer pocket, is setup in an heating mantle inside an efficient hood. Benzoyl chloride (260 g, 1.85 mol) is charged to the flask followed by 1,4-dichlorobenzene (300 g, 2.04 mol). The reaction mixture was slowly raised to about 75-80 ^oC to get a homogeneous solution. At this point, aluminium chloride (550g, 4.11 mol) was added slowly through the side neck over a period of 10-15 min. The resulting mass was heated slowly and raised to 140 ^oC over a period of 1h and maintained at this temperature for 15 min and then slowly raised to 170-175 ^oC over 30-45 min. During the process lots of HCl evolution is observed. The heating was stopped and the reaction mass was cooled to about 80 ^oC over 2 hours and poured into 3 Lt water + 1Lt concentrated hydrochloric acid containing about 2 kg of ice in 10-15 min (more ice can be used if required). The organic solid thus obtained was filtered and  dissolved in toluene (1000 mL). This toluene was washed with water (1000 mL), and 10% sodium carbonate solution (1000 mL 2 times).  Toluene was removed under vacuum to get a viscous mass (~500-550g). The residue thus obtained was dissoved and crystalized in hexane:toluene (7:3)  to get about 352 g (76%, based on benzoyl chloride) of pure 2,5-dichlorobenzophenone.

1. There are not many procedures available for acylation of dichlorobenzene. This method is unusual benzoylation at high temperature (140-175 ^oC)
2. Most of the literature procedure gives less than 20% yield for the same transformation.
3. Use of nitrogen atmosphere during the reaction slightly gives better colour product.
4. One has to use only mechanical stirring (as solvent is not used in the reaction, it is difficult to stir with magnetic stirring).

¹H  (400 MHz, CDCl₃): δ  7.55-7.26 (multiplets, 7H)

¹³C (100 MHz, CDCl₃) : δ 192.86, 139.32, 137.15, 133.00, 132.90, 132.75, 132.25, 131.75, 131.04, 130.75, 130.36, 126.98.

1. Ying Wang, San Dimas, Mark S. Trimmer, Monrovia,  US Patent: US5210313