5724-16-3

The reaction of sulfur trioxide with derivatives of benzene and naphthalene containing an electron-withdrawing substituent, viz.-SO3H, -SO2Ph, -NO2, -CHO, -COPh, -CO2H, and -CO2Me, in dichloromethane as solvent at ca. 22 deg C 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 (3-S) and subsequently, with the exception of nitrobenzene and methyl benzoate, small amounts of 3,5-S2.Benzenesulfonic acid in addition undergoes sulfonylation giving 3,3'-di- and 3,5,3'-trisulfodiphenyl sulfone.Monosulfonation of naphtalene-1-S yields the 1,5-S2, 1,6-S2 and 1,7-S2 derivatives in a ratio of 71:20:9.On using a large excess of SO3, the eventual products are 1,3,5-S3, 1,3,6-S3 and 1,3,5,7-S4.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-nitronaphtalene only the 5-S.The absence of peri sulfonation with 1-sulfo-, 1-benzoyl- and 1-nitronaphthalene is due to prohibitive steric hidrance. 1-Naphthoic acid and its methyl ester upon SO3 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 α- and β-positions, and the steric and electronic effects of the deactivating substituent.

The sulfonation in 98.5percent H2SO4 at 25.0 deg C of naphthalene-1-sulfonic acid yields 58percent 1,5-, 32percent 1,6-, and 10percent 1,7-disulfonic acids and that of the 2-sulfonic acid 4percent 1,3-, 74percent 1,6-, 18percent 1,7-, and 4percent 2,6- + 2,7-disulfonic acids.Further sulfonation of the latter disulfonic acid mixture in 105.2percent H2SO4 at 25.0 deg C yields 78percent 1,3,6- and 12percent 1,3,5- + 1,3,7-trisulfonic acids.Reaction of naphthalene-1,5-disulfonic acid with 105.2percent H2SO4 at 25 deg C yields 5-sulfonaphthalene-1-sulfonic anhydride.Partial rate factors for the sulfonation of naphthalene-1- and -2-sulfonate in highly concentrated aqueous sulfuric acid (where the sulfonating entity is H2S2O7) are reported.They are discussed in terms of the difference in the reactivity of the α- and β-positions of the naphthalene skeleton and the electronic and steric effects of the sulfonate substituent already present.