GB893732A - Process for preparing vinylaromatic sulfonic acid salts - Google Patents

Abstract

A process for producing vinyl aromatic sulphonic acid salts comprises the sulphonation of a b -haloethyl aromatic compound with sulphur trioxide in the presence of a polychlorinated aliphatic liquid hydrocarbon and subsequent dehydrohalogenation by treatment with an excess of an aqueous alkali characterized in that the polychlorinated aliphatic liquid hydrocarbon is removed from the alkaline reaction mixture by distillation. The aromatic reactant may be a chloro- or bromo-ethyl benzene or naphthalene which may be ring substituted, e.g. by alkyl groups and/or chlorine atons and the preferred solvent is methylene chloride which may be removed by flash distillation. The reaction is preferably carried out by reacting the haloethyl aromatic with 1-2 mols boron oxide-free sulphur trioxide at -20 DEG C. to +80 DEG C., adding up to 5 weight per cent water to hydrolyse anhydride by-products, treating the mixture an amount of aqueous alkali metal hydroxide solution in excess of that required to neutralise excess sulphonation acid, sulphonic acid product and the hydrogen, halide evolved in the dehydrohalogenation step distilling off the polychlorinated aliphatic liquid hydrocarbon, separating insoluble material from the reaction medium and heating the resulting aqueous mixture at about 50 DEG C. to 100 DEG C. in the presence of oxygen to minimize polymer formation until dehydrohalogenation is complete. The salt may then be recovered from the aqueous solution, for example, by crystalisation or spray drying. Examples describe the preparation of sodium styrene sulphonate, sodium vinyl toluene sulphonate and sodium dichlorostyrene sulphonate. Reference has been directed by the Comptroller to Specification 815,215.