The reaction of benzenesulfonic acid, dihenyl sulfone , nitrobenzene, benzaldehyde, benzoic acid, methyl benzoate and benzophenone with sulfur trioxide in dichloromethane at room temperature has been studied by analysis of the resulting mixtures of the sulfo derivatives with ^1H NMR. The initial sulfonation of the benzene derivatives yields the corresponding 3-sulfonic acid, further sulfonation yield small amunts of 3,5-disulfonate derivatives. Sulfonation of nitrovenzene yields only the 3-sulfonate derivatives the reaction of benzenesulfonic acid with 2.0 moles of SO~3 yields 3,3-di and 3,5,3-trisulfodiphenyl sulfone.

Key words: SULFONATION, AROMATIC COMPOUNDS, SULFUR TRIOXIDE, PASSIVATION