Background and overview of the preparation method of 3,5-dimethyl-2,6-dibromopyridine
Pyridine and its derivatives are widely distributed in nature. Many plant ingredients such as alkaloids contain pyridine ring compounds in their structures. They are the basis for the production of many important compounds, such as medicines, pesticides, dyes, surfactants, rubber additives, feed additives, food additives, adhesives, etc. Indispensable raw materials in production. 3,5-Dimethyl-2,6-dibromopyridine is an important intermediate in organic synthesis. It is mainly used as pharmaceutical intermediates, organic synthesis, and organic solvents. It can also be used in dye production, pesticide production, and spices. At present, the reported synthesis methods of 3,5-dimethyl-2,6-dibromopyridine have shortcomings such as low yield and long process route.
Preparation method of 3,5-dimethyl-2,6-dibromopyridine
3,5-Dimethyl-2,6-dibromopyridine is prepared as follows:
1) Using 3,5-dimethyl-2-aminopyridine as raw material, add 0.1 mol of 3,5-dimethyl-2-aminopyridine and 0.13 mol of acetic anhydride into a 250 ml four-necked flask, oil Heat the bath to reflux and use thin layer chromatography to track the reaction. When the reaction solution cools down to below 23°C, slowly add 0.11 mol of liquid bromine dropwise. After the addition is completed, react at 40°C for 3 hours. Then add water to the system until all solids are dissolved. , slowly add 40ml of 35% sodium hydroxide solution dropwise, continue the reaction for 20 minutes after the addition, suction filtration, drying, and recrystallization to obtain 3,5-dimethylammonium bicarbonate-2-amino 6-bromopyridine. The recrystallization method is The solvent was methanol, and the molar yield was 65%.
2) Add 50 ml of 45% hydrobromic acid solution to a 200 ml three-necked bottle equipped with a stirrer and thermometer, dissolve 0.048 mol of copper bromide in the hydrobromic acid solution of chloropyridine, and maintain the temperature in an ice water bath at -3 ℃, slowly add 0.04 mol of 3,5-dimethyl-2-amino-6-bromopyridine, maintain the temperature for 15 minutes, slowly add 12.5 ml of saturated sodium nitrite solution dropwise, stir for 3 hours after the addition, and use 35% hydroxide Neutralize the sodium solution to pH=7-8, and distill under reduced pressure to obtain the product with a yield of 63%
