Background and overview of the preparation method of 3-chloropyridine
3-Chloropyridine is an important fine chemical intermediate, which is widely used in the fields of medicine and pesticides. 3-chloropyridine can be made from 2,6-dichloropyridine as raw material, first chlorinated to prepare 2,3,6-trichloropyridine, and then hydrogenated and selectively dechlorinated to obtain 3-chloropyridine.
Preparation method of 3-chloropyridine
Preparation method of 3-chloropyridine Step 1. Chlorination reaction
Weigh 1480.0g of 2,6-dichloropyridine and 89.2g of anhydrous FeCl 3 and place them in a 2000ml four-necked flask. Mix and heat up. When the temperature reaches 120~140℃, add in Chlorine gas, after the reaction is sufficient, cool down to 100°C, distill under reduced pressure, collect the product fraction at -0.1MPa, top temperature 118~124°C, the low-concentration distillate produced during the distillation process can also be applied to the next batch Re-react or apply to the next batch and re-distillate and purify. After application, 1715.0 g of 2,3,6-trichloropyridine was finally obtained. After application, the total yield was 94.0%, and the purity was ≥99.5%.
Preparation method of 3-chloropyridine, step 2, hydrogenation reaction
Put 557.8g of 2,3,6-trichloropyridine, 232.0g of triethylamine, 8.5g of palladium carbon, and 1675g of toluene obtained in the chlorination reaction into the reactor at one time, and raise the temperature to 60~80°C , hydrogen gas is introduced to carry out the hydrogenation reaction. When the pH of the reaction solution is measured to be 4 to 8, the hydrogen gas is stopped and the hydrogenation reaction is completed.
Preparation method of 3-chloropyridine, step 3, post-treatment operation
Reduce the above reaction solution to room temperature, add 790g of water to dissolve triethylamine hydrochloride, filter, add 30g of water and 30g of toluene to wash the filter cake, which is palladium carbon. The filtrate was allowed to stand for stratification, and the water layer was removed; extract it three times with 200g hydrochloric acid and then stratify. The extracted solution can be recycled to the next batch of reactions by adding 2,3,6-trichloropyridine and toluene, and adding 2,3,6-trichloropyridine and toluene to the extracted solution. Add 1630g of water to hydrochloric acid to dilute, filter, and then wash with 100g of water (the wastewater generated after washing can be recycled and used in the extraction stage). Add alkali to adjust the pH of the filtrate to neutral, and layer it to obtain 3-chloropyridine. After application, the total mass of the product is 297.2g, the yield is 85.6%, and the purity is ≥99.5 hydroxypyridine%.
Preparation method of 3-chloropyridine Separation method of 2-chloropyridine and 3-chloropyridine
A method for separating 2-chloropyridine and 3-chloropyridine, using a bisdibromoethoxy column [6] aromatic hydrocarbon crystal material to adsorb and separate a mixture of 2-chloropyridine and 3-chloropyridine.
Since the different substitution positions of chlorine atoms on the pyridine ring lead to structural differences between 2-chloropyridine and 3-chloropyridine, the bis-dibromoethoxy pillar[6]arene crystal material can be compared with 2-chloropyridine. -Chloropyridine forms a host-guest complex with a stoichiometric ratio of 1:2. Since the host-guest interaction is a weak non-covalent interaction, the complex is unstable. When heated, the host-guest decomplexes and 2-chloropyridine is released. The bisdibromoethoxy column [6] aromatic crystal material is stable at the desorption temperature and can be reused after desorption is completed, and the selectivity effect will not decrease.
The preparation method of the bisdibromoethoxy column [6] aromatic crystal material includes: adding 1,1-dibromoparaphenylene diethyl ether into the 1,2-dichloroethane solvent, and adding Lewis acid , react at 25-30°C for 20-30 minutes. After the reaction is completed, it is quenched with a saturated solution of sodium bicarbonate, washed with water, separated and concentrated to obtain a crude product. The crude product is separated by column chromatography to obtain bisdibromoethoxy column [ 6] Aromatic hydrocarbons.
The bisdibromoethoxy column [6] aromatic crystal material separated by column chromatography can be activated by removing solvent molecules by drying under vacuum and reduced pressure at 110-130°C overnight. The activated bisdibromoethoxy column [6] aromatic crystal material can be directly used for the adsorption separation of 2-chloropyridine and 3-chloropyridine.
References
[1] [China invention, China invention authorization] CN201110059687.2 A preparation method of 3-chloropyridine
[2] [China invention, China invention authorization] CN201910536826.2 A method for separating 2-chloropyridine and 3-chloropyridine
