Process for preparing sulfonic acid fluorides

In a process for preparing sulfonic acid fluorides by reacting sulfonic acid halides with inorganic fluorides in an organic aqueous phase, the improvement comprising carrying out the reaction of a sulfonic acid halide having the structure

• R--SO.sub.2 --X
• in which
• X is bromine or chlorine and
• R is a straight-chain, branched or cyclic hydrocarbon radical of 1-28 C atoms which can simultaneously contain chain and cyclic structural elements, saturated, unsaturated or aromatic, which can be further substituted by --SO.sub.2 X--groups, fluorine, chlorine, bromine, iodine, oxygen, sulphur, nitrogen and/or phosphorus, one or more of which being arranged in and/or on a ring or in and/or on a chain
• with an inorganic fluoride in a water immiscible inert organic solvent in the presence of a catalytic amount of an amine having the structure ##STR3## in which R.sub.1, R.sub.2, and R.sub.3 are independently selected from the group consisting of alkyl, alkyl substituted by hydroxy or lower alkoxy, alkenyl, cycloalkyl, cycloalkyl substituted by hydroxy or alkyl, aralkyl, aralkyl substituted by halogen, alkyl or lower alkoxy, aryl, aryl substituted by lower alkyl, methoxy or halogen, or conjointly R.sub.1, R.sub.2 and/or R.sub.3 combined with the nitrogen and/or additional hetero-atoms selected from the group consisting of oxygen, sulphur or nitrogen, form a 5-membered or 6-membered heterocyclic structure,
• or in the presence of a catalytic amount of an onium salt having the formula ##STR4## in which L is nitrogen or phosphorous;
• R.sub.4, R.sub.5, R.sub.6 and R.sub.7 are independently selected from the group consisting of alkyl, aralkyl substituted by C.sub.1 -C.sub.4 alkyl, methoxy or halogen, aryl, and aryl substituted by C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.2 alkoxy or halogen, or alternatively, two adjacent radicals amongst R.sub.4, R.sub.5, R.sub.6 and R.sub.7 and including the central atom L, form a 5 or 6-membered heterocyclic structure which can additionally contain a further hetero atom selected from the group consisting of oxygen, sulfur or nitrogen;
• and X.sup.- is a halide, cyanide or hydroxyl ion.