Dry gaseous hydrogen bromide is introduced to 70 ml. of anhydrous dimethylsulphoxide at room temperature. The amount of the introduced hydrogen bromide is measured by titrating against 0.1N sodium hydroxide solution. The hydrogen bromide is introduced until reaching a hydrogen bromide content of 0.0003 to 0.0005 mole/ml. in the dimethylsulphoxide. Then 10 g (0.01737 mole) of α-ergocryptine are dissolved in an amount containing 12 equivalents of hydrogen bromide as taken out from the thus-obtained mixture containing hydrogen bromide in dimethylsulphoxide. The reaction mixture is stirred at room temperature for 15 minutes beginning from the complete dissolution of α-ergocryptine, then poured in 5 volumes of water as calculated for the volume of dimethylsulphoxide. Then the mixture is alkalinized to a pH value of 8 to 9 by adding ammonium hydroxide, the precipitated 2-bromo-α-ergocryptine is filtered off, washed twice with 10 ml. of water each, dissolved in 200 ml. of dichloromethane and dried over anhydrous sodium sulphate. After filtering off the drying agent, 200 ml. of diisopropyl ether are added to the solution and dichloromethane is distilled off under atmospheric pressure. 2-bromo-αergocryptine separated from the distillation residue is filtered off and washed to give a yield of 8.4 g. (74%), m. p.: 215°-217° C., [α]D20 =-190° c=1%, dichloromethane).
