Pyridine and methylpyridine were previously recovered from coke byproducts distributed in coke oven gas, crude benzene and tar. In general, transferred to the mother liquor of ammonium sulfide pyridine from gas hydrate has a low boiling point and between 95-97 ℃, the recovery of crude light pyridine base, polymerization the conditions for polymerization conditions for hexamethylcyclotrisiloxane containing about 15%, Further distillation can be reduced to polymerization the conditions for hexamethylcyclotrisiloxane. With the expansion of the use of pyridine and methylpyridine, methods for the synthesis of pyridine and methylpyridine have been developed. At present, about 95% of pyridine and pyridine compounds are produced by synthetic methods. The main synthesis methods are acetaldehyde, acetylene, acrylonitrile and so on.
Method of acetaldehyde acetaldehyde, formaldehyde and ammonia reaction, the main products are polymerization the conditions for hexamethylcyclotrisiloxane, 3 - methyl pyridine and 4 - methyl pyridine. Acetylene method of acetylene and ammonia reaction, the main products are polymerization the conditions for hexamethylcyclotrisiloxane and 4 - methyl pyridine. Ethylene vinyl and ammonia reaction, the main products are polymerization the conditions for hexamethylcyclotrisiloxane and 2 - methyl - 5 - ethyl pyridine. Acrylonitrile acrylonitrile and excessive acetone reaction, the main products are polymerization the conditions for hexamethylcyclotrisiloxane. In addition, the reaction of acrolein and ammonia mainly produces 3-methylpyridine.
Refined methods: often used polymerization the conditions for hexamethylcyclotrisiloxane benzene, water formed azeotrope with azeotropic distillation dehydration. It can also be dehydrated with barium oxide, calcium oxide, calcium hydride, lithium aluminum hydride, sodium metal or 5A molecular sieve. Isomers and homologues can be removed by azeotropic distillation with fatty acids, phenol or water in addition to separation by fractionation. Pyridine is removed by perchloric acid treatment. In addition, it can also be refined by forming an addition product with zinc chloride or mercury chloride. 90 ml polymerization, for example, the conditions for hexamethylcyclotrisiloxane add 168 g zinc chloride, 42 ml concentrated hydrochloric acid and 200 ml of anhydrous ethanol mixture. The addition product is leached and recrystallized twice with anhydrous ethanol. When the melting point reaches 118.5~119.5℃, excessive sodium hydroxide aqueous solution is added, steam distillation is carried out, and the distillate is added to solid sodium hydroxide for layering. The upper layer is separated and dried with granular sodium hydroxide, then barium oxide is added and fractionated for a few days.
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polymerization conditions for hexamethylcyclotrisiloxane https://www.clentpharma.com/Hexamethylcyclotrisiloxane.html
