Abstract: The reactions of benzenesulfonic acid,diphenyl sulfone,nitrobenzene,benzaldehyde,benzoic acid, methyl benzoate and benzophenone with SO₃using dichloromethane as the solvent at room temperature were studied by analysis of the resulting mixtures of the sulfonated derivatives with ¹HNMR. The initial sulfonation of the benzene derivatives yields the corresponding 3-sulfonic acid.With the exception of nitrobenzene and methyl benzoate,small amounts of 3, 5-disulfonic acid,in addition, undergoes sulfonation giving 3,3-di and 3,5,3'-trisulfodiphenyl sulfone.

Key words: Deactivated benzene, Sulfur trioxide, Aromatic sulfonation