The reaction of sulfur trioxide with deactivated naphthalene derivatives containing an electron withdrawing substituent , viz. -SO~3H, -CHO, -COPh, -CO~2H, and -CO~3Me, in diehloromethane as solvent has been studied by analysis of the resulting mixtures of the sulfo derivatives with ^1H NMR. Monosulfonation of naphthalenesulfonic acid yields 1,5-disnlfonie acid (1,5-S~2), 1,6-S~2 and 1,7-S~2. On using a large excess of SO~3, the eventual products are 1,3,5-S~3, 1,3,6-S~3 and 1,3,5,7-S~4. Monosulfonation of 1-formylnaphthalene yields 5-S,6-S,7-S and 8-S, in a 55:9:6:30 ratio, that of 1-benzoylnaphslene 5-S, 6-S and 7-S in a ratio of 83:11:6, and 1-nitronaphthalene only 5-S. 1-napthoic acid and its methyl ester upon SO~3 sulfonation and aqueous workup both yield 5- and 8- sulfonaphthoic acid in a ratio of 65:35 and 77:21 respectively. The initially formed peri substituted product is the intramolecular anhydride of 8-sulfo-1-naphthoic acid. All the 2-substituted naphthalenes upon SO~3 sulfonation yield 5-S and8-S, of which the former sulfoisomer is far in excess.

Key words: SULFONATION, SULFUR TRIOXIDE