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d) 812 g (14 mol) of potassium fluoride and 1400 ml of tetramethylene sulphone are subjected to incipient distillation at 20 mbar (quantity of distillate: 100 ml) in a stirred V4A steel apparatus. Then 40 g of tetraphenylphosphonium bromide and a mixture of 795 g (2.8 mm) of 2H-tetrachlorobenzotrifluoride and 170 g (0.78 mm) of 5-chloro-2,3,4-trifluorobenzotrifluoride are added and the mixture is stirred for 18 hours at 210 C. under the autogenous pressure (max. pressure 3.4 bar). Distillation yields 747 g of a crude distillate which is redistilled in a rotating strip column. 396 g of 2H-tetrafluorobenzotrifluoride and 318 g of 5-chloro-2,3,4-trifluorobenzotrifluoride are obtained. The recovery rate of the isolated yield is 90.5%.
18a. 2-fluoro-3-methyl-5-nitropyridine 2-Chloro-3-methyl-5-nitropyridine (15 g, 86.9 mmol; from Maybridge Chemical Co.), KF (12 g, 258 mmol) and tetraphenylphosphonium bromide (20 g, 47.7 mmol; Aldrich) were combined in 200 mL of acetonitrile and heated at reflux for 4 days. The mixture was diluted with Et2 O (500 mL) and filtered, and the filtrate was concentrated. The residue was triturated with hot hexane (4*200 mL), and the hexane solutions were combined and concentrated to afford the title compound as a solid (8.4 g, 60%): 1 H NMR (DMSO-d6, 300 MHz) delta2.42 (s, 3H), 8.43 (m, 1H), 8.95 (dd, J=1.6 Hz, 1H); MS (CI/NH3) m/z: 157 (M+H)+.
Comparison Example 6 Preparing 2,4-difluoronitrobenzene by Reacting 2,4-dichloronitrobenzene Using tetraphenylphosphonium bromide as Catalyst 192 g (1 mol) of 2,4-dichloronitrobenzene, 550 ml of tetramethylene sulfone, 136.8 g (2.4 mol) of potassium fluoride and 6.29 g (0.015 mol) of tetraphenylphosphonium bromide are employed and the procedure described in Example 7 and 8 is followed.
Comparison Example 1 Preparing 4-nitrofluorobenzene by Reacting 4-nitrobenzene Using tetraphenylphosphonium bromide as Catalyst 157 g (1mol) of 4-nitrochlorobenzene, 400 ml of tetramethylene sulfone, and 62.7 g (1.1 mol) of potassium fluoride, but 4.19 g (0.01 mol) of tetraphenylphosphonium bromide, are employed and the procedure described in Example 1 is followed.
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