Hydrofluoric Acid → 2,5-Dichloro-3-fluoropyridine

Participants

Reaction Steps

A Monel autoclave is charged with 450 ml (22.5 mol) of hydrogen fluoride and then 163 g (1.0 mol) of 3-amino-2,5-dichloropyridine are added at a temperature in the range from -5° to -1° C. Over 11/2 hours, 82.8 g (1.2 mol) of sodium nitrite are introduced into this solution. After the reaction mixture has been stirred at the same temperature for 11/2 hours, the temperature is raised stepwise to +60° C. When the evolution of gas ceases, the hydrogen fluoride is evaporated off and the residue is taken up in methylene chloride and the resultant solution is poured into ice water. The two-phase mixture is neutralised with concentrated ammonia solution. The organic phase is separated and the aqueous phase is extracted three times with methylene chloride. The combined organic phases are washed with water, dried over magnesium sulfate, treated with active carbon, filtered through silica gel and concentrated by evaporation, affording 141.5 g (85% of theory) of 2,5-dichloro-3 -fluoropyridine, m.p. 38°-39° C.

Provenance & Evidence