Abstract: The invention relates to a process for the preparation of fluorinated compoundsAz.sub.x ArF.sub.w Cl.sub.(y-w) R.sub.z (1)in which Az is a radical --F, --Cl, --Br, --NO.sub.2, --CN, --CF.sub.3, --CCl.sub.3, --CHO, --CO(C.sub.n H.sub.2n+1), --COX or --SO.sub.2 X, where X is F, Cl or Br, x is an integer from 1 to 3, Ar is a phenyl radical, pyridyl radical or naphthyl, w is an integer from 1 to y, y is an integer from 1 to 5, R is H, an alkyl radical or an alkoxy radical having from 1 to 10 carbon atoms, z is an integer from 1 to 5, (x+y+z) is the number of all substitutable valences on the radical Ar, which comprises reacting a compoundAz.sub.x ArCl.sub.y R.sub.z (2),with an alkali metal fluoride in the presence of a component a) or a mixture of component a) and at least one of components b), c), d) and/or e), component a) being one or more quaternary ammonium compounds which contain one or more radicals --(C.sub.m H.sub.2m O)R.sup.