On the intermediacy of phenyl hydrogen sulfates in the sulfonation of phenols. Sulfonation of phenol, anisole, methyl phenyl sulfate, the 2-halogenophenols, a series of phenyl methanesulfonates together with 2,6-dimethylaniline and its N-methylsulfonyl derivative

Article abstract of DOI:10.1002/recl.19881071204

The sulfonation of methyl phenyl sulfate (4) with concentrated aqueous sulfuric acid at 25 deg C yields the 4-sulfonic acid.This initial product then decomposes to give phenol-4-sulfonic acid, which is subsequently sulfonated to phenol-2,4-disulfonic acid.From the first-order-rate coefficients obtained for sulfonation of phenyl methanesulfonate (3) and (4) in 93,2percent H2SO4, for which acid concentration the sulfonating entity is H2S2O7, the ?_p⁺ values of the OSO2Me and OSO2OMe substituents have been determined to be 0.40 and 0.46, respectively.The sulfonation of both 2-chlorophenyl (10) and 2-methylphenyl methanesulfonate (14) with 2.0 equiv of SO3 in nitromethane at 0.0 deg C yields the 4-sulfonic acid as the exclusive product, whereas 2-methoxyphenyl methanesulfonate (13), under the same conditions, forms exclusively the 5-sulfonic acid. 2-Chloro- (6), 2-bromo- (7) and 2-iodophenol (8) with 1.0 and 4.0 equiv of SO3 in nitromethane yield exclusively the 4-sulfonic acid, while 2-fluorophenol (5) with 2.0 and 5.0 equiv of SO3 yields in addition the 5-sulfonic acid to the extent of 4 and 30percent, respectively.In the reactions of 2,6-dimethylphenol (15) and 2,6-dimethylaniline (17) with at least 1 equiv of SO3 in nitromethane, the 3-SO3H/4-SO3H ratio was found to increase on increasing the relative amount of SO3.For both 15 and 17, the limiting 3-SO3H/4-SO3H ratio at high SO3/ArOH ratios is 86/14 and this value is considered to be the ratio for the sulfonation of both 2,6-dimethylphenyl hydrogen sulfate and 2,6-dimethylaniline-N-sulfonic acid.This assumption is supported by the observation that the sulfonation of 2,6-dimethylphenyl methanesulfonate (16) and N-(methylsulfonyl)-2,6-dimethylaniline (18) with SO3 leads to a similar 3-SO3H/4-SO3H ratio.