THE POSITIONAL REACTIVITY ORDER IN THE SULFUR-TRIOXIDE SULFONATION OF BENZENE AND NAPHTHALENE DERIVATIVES CONTAINING AN ELECTRON-WITHDRAWING SUBSTITUENT

Abstract

The reaction of sulfur trioxide with derivatives of benzene and naphthalene containing an electron-withdrawing substituent, viz.-SO3H, -SO(2)Ph, -NO2, -CHO, -COPh, -CO2H, and -CO(2)Me, in dichloromethane as solvent at approximate to 22 degrees C has been studied by analysis of the resulting mixtures of the sulfo derivatives with H-1-NMR. The initial sulfonation of the benzene derivatives yields the corresponding 3-sulfonic acid (3-S) and subsequently, with the exception of nitrobenzene and methyl benzoate, small amounts of 3,5-S-2. Benzenesulfonic acid in addition undergoes sulfonylation giving 3,3'-di- and 3,5,3'-trisulfodiphenyl sulfone. Monosulfonation of naphthalene-1-S yields the 1,5-S-2, 1,6-S-2 and 1,7-S-2 derivatives in a ratio of 71:20:9. On using a large excess of SO3, the eventual products are 1,3,5-S-3, 1,3,6-S-3 and 1,3,5,7-S-4. Monosulfonation of naphthalene yields 5-S, 6-S, 7-S and 8-S in a 55:9:6:30 ratio, that of 1-benzoylnaphthalene 5-S, 6-S and 7-S in a ratio of 83:11:6, and 1-nitronaphthalene only the 5-S. The absence of peri sulfonation with 1-sulfo-, 1-benzoyl- and 1-nitronaphthalene is due to prohibitive steric hindrance. 1-Naphthoic acid and its methyl ester upon SO, sulfonation and aqueous work-up 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 (5). All the 2-substituted naphthalenes yield 5-S and 8-S upon SO3 sulfonation of which the former sulfo isomer is far in excess. The positional reactivity orders for the SO3 sulfonation of the monosubstituted naphthalene derivatives are discussed in terms of the difference in reactivity of the alpha- and beta-positions, and the steric and electronic effects of the deactivating substituent.