A process for the production of an arylsulphonium salt, comprising reacting an aromatic compound of the formulaAr--Hin which Ar is an aromatic radical with a sulphoxide of the formula ##STR1## in which R.sup.1 and R.sup.2 each independently is an aliphatic or aromatic radical or, together, a divalent radical, in the presence of hydrogen fluoride. The products are known and can be converted to arylthioethers which are intermediates for other known syntheses.