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

The reaction of sulfur trioxide with derivatives of benzene and naphth alene containing an electron-withdrawing substituent, viz.-SO3H, -SO(2 )Ph, -NO2, -CHO, -COPh, -CO2H, and -CO(2)Me, in dichloromethane as sol vent at approximate to 22 degrees C has been studied by analysis of th e resulting mixtures of the sulfo derivatives with H-1-NMR. The initia l sulfonation of the benzene derivatives yields the corresponding 3-su lfonic acid (3-S) and subsequently, with the exception of nitrobenzene and methyl benzoate, small amounts of 3,5-S-2. Benzenesulfonic acid i n addition undergoes sulfonylation giving 3,3'-di- and 3,5,3'-trisulfo diphenyl 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 l arge 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 abse nce of peri sulfonation with 1-sulfo-, 1-benzoyl- and 1-nitronaphthale ne is due to prohibitive steric hindrance. 1-Naphthoic acid and its me thyl 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 anhydr ide of 8-sulfo-1-naphthoic acid (5). All the 2-substituted naphthalene s yield 5-S and 8-S upon SO3 sulfonation of which the former sulfo iso mer is far in excess. The positional reactivity orders for the SO3 sul fonation of the monosubstituted naphthalene derivatives are discussed in terms of the difference in reactivity of the alpha- and beta-positi ons, and the steric and electronic effects of the deactivating substit uent.