Mild electrophilic halogenation of chloropyridines using CCl4 or C2Cl6 under basic phase transfer conditions

Effective chlorination of 2,3,5,6-tetrachloropyridine to pentachloropyridine was realized under mild phase transfer conditions with carbon tetrachloride and 50% NaOH or solid K3PO4. Mechanistic study of this reaction indicated the possibility of an aromatic carbanionic intermediate. Hexachloroethane was established as a more selective electrophilic chlorination agent.