Preparation of isomer-free 2,5-dichloro-pyridine

摘要

A process for the preparation of isomer-free 2,5-dichloropyridine comprising alkoxylating 2-chloro-pyridine or 2-bromo-pyridine in the presence of a base at elevated temperatures, chlorinating with gaseous chlorine the alkoxylated product at ambient temperatures in an aqueous suspension in the presence of an auxiliary base, a small amount of a catalyst and optionally a small amount of an emulsifier, treating the isomer reaction mixture with a Vielsmeyer-Haack reagent, subjecting 2,5- and 2,3-dichloropyridine mixture to water vapor distillation and crystallizing the crystalline product from an alcohol-water mixture.