Calcium Carbonate → 3,4-Difluorobenzaldehyde

3,4-difluorotoluene (25.6 g, 0.2 mol) is heated to 105° C. in a 250 ml 3-necked flask equipped with a magnetic stirrer, thermometer, condenser, and dropping funnel, and is illuminated as bromine (67 g, 0.42 mol) is added slowly. The temperature is kept between 105-110° C. while the first half of the bromine is added over a period of one hour. The rest of the bromine is added over approximately a two-hour period, and the temperature is raised to 150° C., and is kept there for 5 minutes. The reaction mixture is cooled and is transferred to a 1 liter 3-necked flask with a motor-driven stirrer and condenser. H2O (120 ml) and calcium carbonate (90 g) are added, and the mixture is refluxed for 20 hours with good stirring. The reaction mixture is steam distilled until no further oil is collected. The oil is taken up in methylene chloride and dried over MgSO4. Evaporation of the solvent yields 3,4-difluorobenzaldehyde that is used without further purification.