The reaction of deactivated naphthalene derivatives with sulfur trioxide
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The reaction of sulfur trioxide with deactivated naphthalene derivatives containing an electron withdrawing substituent, viz. -CHO, -COPh, -CO2H, and -CO(2)Me, in dichloromethane as the solvent has been studied by analysis of the resulting mixtures of the sulfo derivatives with H-1 NMR. Monosulfonation of 1-formylnaphthalene 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 5-S. 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. All the 2-substituted naphthalenes upon SO3 sulfonation yield 5-S and 8-S.