Aromatic fluorine compounds. XI. Replacement of chlorine by fluorine in halopyridines

The α-halogenated pyridines react with potassium fluoride in various solvents to give replacement of the α-halogen by fluorine. A 50% yield of 2-fluoropyridine was obtained from 2-chloropyridine by heating with potassium fluoride in dimethyl sulfone or tetramethylene sulfone for twenty-one days; 2-bromopyridine gave a similar yield with a heating period of only seven days. The α-halogens of the polyhalopyridines undergo the exchange reaction more readily than do the halogens of the α-monohalopyridines. The proposed structures of the fluoropyridines are supported by alternate syntheses and by n.m.r. studies.