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.5, component b) being an amidophosphonium salt, component c) being a quaternary ammonium salt, component d) being a quaternary phosphonium salt, component e) being a polyether, and carrying out the reaction at from 50 to 250.degree. C., removing the compound of the formula (1) formed during the reaction by distillation, and the compound of the formula (2) is fed to the reaction mixture at a rate corresponding to the rate at which the compound of the formula (1) is removed.