Reactions of sulfur trioxide with benzene derivatives containing a deactivating oxy substituent

Abstract

The reactions of phenyl acetate (2), (trifluoromethoxy)benzene (3), (difluoromethoxy)-benzene (4), 4-(trifluoromethoxy)phenol (5), 4-(trifluoromethoxy)phenyl methanesulfonate (6), 4-(trifluoromethoxy)anisole (7) and 3-(trifluoromethoxy)anisole (8) with SO3, in nitromethane have been studied. Upon reaction with SO3, 2 yields 2-4-sulfonic acid (2-4-S); subsequently, transfer of the acetyl group takes place to yield the mixed anhydride of phenol-4-pyrosulfonic acid and acetic acid (9) or the corresponding hydrogen sulfate 10, depending on the amount of SO3, used. Reaction of the α-fluorinated anisoles 3 and 4 with SO3 leads to sulfonation at the 4-position only; however, on using both a high substrate concentration and an excess of SO3, some 2,4-S2, is formed with 4 but not with 3. On reaction of 5 with 0.8 mol-equiv of SO3, in C2H3NO2, the hydrogen sulfate derivative (5-O-S) is formed; at 100°C, some isomerization to 5-2-S occurs. Upon reaction with 4.0 mol-equiv of SO3, the initially formed hydrogen sulfate slowly yields the corresponding 2-sulfophenyl hydrogen sulfate (5-O,2-S2). On using 6.0 mol-equiv of SO3, the 5-O,2-S2 is slowly converted into 6-(trifluoro-methoxy)benzo-1,3,2,4-dioxadithiin 2,2,4,4-tetraoxide (11). Reaction of 6 with either 0.9 or 3.0 mol-equiv of SO3, initially leads to insertion of sulfur trioxide in between the SO2CH3, and the adjacent O, yielding the 4-(trifluoromethoxy)phenyl methanepyrosulfonate 12. This species subsequently yields 13 and 14. Reaction of 7 with SO3 leads to sulfonation only at the 2-position; eventually some sulfodemethylation to yield 5-2-S takes place. Reaction of 8 with 1.0 mol-equiv of SO3, yields a 68: 32 mixture of 8-4-S and 8-6-S.