the components of aqueous ammonium fluoride solutions are recovered as ammonia and potassium fluoride by adding potassium hydroxide , distilling to remove and secure the ammonia , concentrating the remaining solution and combining it with a water soluble , dipolar , aprotic solvent , such as n - methylpyrrolidone , and distilling to remove the remaining water to obtain the potassium fluoride as a slurry in the solvent . slurries of potassium fluoride are useful in the replacement of chloride in heterocyclyl and aryl chlorides by fluoride .