S(=O)(=O)(O)O.O.[Br:7][C:8]1[CH:9]=[C:10]([CH:13]=[CH:14][C:15]=1[F:16])[CH2:11][OH:12].[Cr](O[Cr]([O-])(=O)=O)([O-])(=O)=O.[K+].[K+]>CCCCCCCC[N+](CCCCCCCC)(CCCCCCCC)C.[Cl-].C(Cl)Cl>[Br:7][C:8]1[CH:9]=[C:10]([CH:13]=[CH:14][C:15]=1[F:16])[CH:11]=[O:12]A misture of 29.4 g (0.3 mol) of sulphuric acid, 50 ml of water and 2 ml of Aliquat 336 (tricapryl-methyl-ammonium chloride) was added to a solution of 20.5 g (0.1 mol) of 3-bromo-4-fluoro-benzyl alcohol in 250 ml of methylene chloride at room temperature. Thereafter, 9.7 g (0.033 mol) of potassium dichromate were added to the reaction mixture and the temperature was kept at about 25° C. for 2 hours by cooling slightly. After adding 100 ml of water, the organic phase was separated off and the aqueous phase was extracted once more with 100 ml of methylene chloride. The organic phases were washed twice with 100 ml of water each time, then once with 100 ml of saturated sodium bicarbonate solution and once more with 100 ml of water, dried over sodium sulphate and evaporated in vacuo. The residue was distilled. 16.3 g (81% of theory) of 3-bromo-4-fluoro-benzaldehyde were obtained in this manner as a colorless oil with a boiling point of 65° C./0.3 mm Hg.
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