1074-24-4

white to slightly yellow shiny crystalline powder

The general procedure for the synthesis of 2,5-dibromo-1,4-dimethylbenzene from p-xylene was as follows: dichloromethane (50 mL) was added to a 150 mL two-necked round-bottomed flask and p-xylene (16.96 g, 0.16 mol, 19.8 mL) was accurately weighed and added to it. Subsequently, iodine (0.1 g, 0.8 mmol) was added to the mixture. An air condenser tube was fitted to one neck of the flask and connected to a tail gas recovery unit; the other neck was fitted with a constant pressure dropping funnel. Accurately measure the liquid bromine (18 mL) and transfer it to the constant-pressure dropping funnel, covering the top layer of the bromine solution with a layer of water (about 0.3-0.5 cm) to prevent volatilization of the bromine. The bottle was stoppered tightly and the temperature of the reaction system was controlled at 12°C under strong stirring and light protection. Slowly add liquid bromine dropwise to the reaction mixture (dropwise addition time is controlled at 40 to 50 minutes), taking care to avoid water droplets entering the reaction solution. The reaction lasted for 18 hours. Upon completion of the reaction, 40 mL of 25% aqueous KOH solution was added and stirred vigorously for 30 minutes. The reaction mixture was transferred to a separatory funnel, and the lower organic phase was separated and washed twice (50 mL each) with deionized water. The organic phase was dried with anhydrous CaCl2, filtered and the solvent was removed under reduced pressure. The residue was recrystallized twice (300 mL each) with ethanol to give white needle-like crystals. The yield was 96.5% (40.44 g).

[1] Patent: CN105085340, 2017, B. Location in patent: Paragraph 0037; 0038
[2] Crystal Growth and Design, 2016, vol. 16, # 7, p. 3993 - 4004
[3] Organic Letters, 2011, vol. 13, # 6, p. 1462 - 1465
[4] Patent: CN107721905, 2018, A. Location in patent: Paragraph 0024
[5] Patent: CN108440386, 2018, A. Location in patent: Paragraph 0041; 0044; 0045