Process for the preparation of 2-aryl-ethane-sulphonic acids

A process for the preparation of 2-aryl-ethane-sulphonic acids and salts thereof, which, in the form of the free acids, correspond to the formula

• Ar.sup.1 --CH.sub.2 --CH.sub.2 --SO.sub.3 H (I),
• in which
• Ar.sup.1 denotes phenyl or naphthyl which are unsubstituted or monosubstituted to trisubstituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, chlorine, bromine or fluorine or a heterocyclic aromatic five-membered or six-membered radical having one or more N atoms as hetero atoms, and are unsubstituted or substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, chlorine, bromine or fluorine
• by reaction of vinyl aromatic compounds of the formula
• Ar.sup.1 --CH.dbd.CH.sub.2 (II),
• in which
• Ar.sup.1 has the above definition, with sulphurous acid or soluble salts thereof or the anhydride thereof in a water-containing medium, wherein the reaction is carried out at a temperature of -15.degree. C. to +65.degree. C. and at a pressure of 0.5 to 5 bar in the presence of an amine of the formula
• N(R.sup.1, R.sup.2, R.sup.3) (III)
• in which
• R.sup.1, R.sup.2 and R.sup.3, independently of each other, denote straight-chain or branched C.sub.1 -C.sub.12 -alkyl, C.sub.3 -C.sub.8 -cycloalkyl, phenyl or substituted phenyl or C.sub.7 -C.sub.10 -aralkyl, where, furthermore, 2 of the radicals R.sup.1, R.sup.2 and R.sup.3 together with the N atom which they substitute can form a, pyrrolidine, oxazolidine, thiazolidine, piperidine or morpholine, where, furthermore, up to two of the substituents R.sup.1, R.sup.2 and R.sup.3 can denote hydrogen and where, furthermore, all three radicals R.sup.1, R.sup.2 and R.sup.3 together with the N atom to which they are attached form a diazabicycloundecane ring or a pyridine ring.