Alkyl fluorides are more conveniently prepared by heating suitable chloro $$-$$ or bromo-alkanes with organic fluorides such as $$As{F_3},\,\,Sb{F_3},\,\,Co{F_2},\,\,AgF,\,H{g_2}{F_2}\,\,$$ etc.

This reaction is called Swarts reaction.

$$C{H_3}Br + AgF\buildrel \, \over \longrightarrow C{H_3}F + AgBr$$

$$2C{H_3}C{H_2}Cl + H{g_2}{F_2}\buildrel \, \over \longrightarrow $$

$$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2C{H_3}C{H_2}F + H{g_2}Cl{}_2$$