Hydrochloric Acid → 3-Bromo-4-fluorobenzaldehyde

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250 g (2.27 mols) of 4-fluorotoluene are added to 1.25 g (7.61 mmols) of α, α'-azoisobutyronitrile and heated to a temperature of 110° C. In the course of 4 hours, 725 g (4.54 mols) of bromine are added dropwise while raising the temperature of the reaction mixture to 145° C. 1.25 g (9.17 mmols) of zinc chloride are added to the mixture substantially consisting of 4-fluorobenzalbromide, and subsequently 40 g of water are added within 6 hours. After cooling to a temperature of 80° C. and addition of 1,160 g (930 ml) of 1,2-dichloroethane, the mixture is cooled to 150° C. Subsequently, 500 g of aluminum chloride are added portionwise to the mixture without exceeding a temperature of 20° C. Then, the mixture is heated to 40° C., and during 6 hours 382 g (2.39 mols) of bromine are added dropwise; afterwards, stirring of the mixture is continued for 16 hours at a temperature of 40° C. The reaction mixture is slowly poured onto a mixture of 2,400 g of ice and 105 g of concentrated hydrochloric acid, and thoroughly stirred for 5 minutes. The organic phase of the mixture is separated and washed twice with water and 10% aqueous sodium carbonate solution, respectively, and once with water. After evaporation of the 1,2-dichloroethane the product is fractionated. There are obtained 210 g (45%, relative to 4-fluorotoluene) of 3-bromo-4-fluorobenzaldehyde with a boiling range of 92° to 98° C. (at a pressure of 17 mbar) and a purity degree of more than 99%.

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