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

  • US 5,380,862 A
  • Filed: 08/23/1993
  • Issued: 01/10/1995
  • Est. Priority Date: 10/07/1992
  • Status: Expired due to Fees
First Claim
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1. A process for the preparation of isomer-free 2,5-dichloro-pyridine comprising alkoxylating at reflux 2-chloro-pyridine or 2-bromo-pyridine in the presence of an alkali metal hydroxide or alkaline earth metal hydroxide at elevated temperatures to form the 2-alkoxy-pyridine, chlorinating with gaseous chlorine the alkoxylated product at ambient temperatures in an aqueous suspension in the presence of an alkali metal or alkaline earth metal hydroxide or oxide as auxiliary bases, a small amount of a catalyst and optionally a small amount of an emulsifier where the auxiliary base is added whenever the pH drops below 7 and the previously added auxiliary base is completely dissolved to form a chloro-2-alkoxy-pyridine isomer reaction mixture, treating the isomer reaction mixture with a Vielsmeyer-Haack reagent, subjecting 2,5- and 2,3-dichloro-pyridine mixture to water vapor distillation and crystallizing the crystalline product from an alcohol-water mixture.

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