Sulfonation and sulfation in the reactions of the chloro‐ and dichlorophenols, 3‐fluorophenol and (2,3‐, 2,4‐ and 3,4‐dichlorophenoxy)acetic acid with concentrated aqueous sulfuric acid and sulfur trioxide

Abstract The chloro‐ and dichlorophenols have been sulfonated with sulfuric acid and with SO3 in aprotic solvents. In the sulfonations with concentrated aqueous sulfuric acid, the sulfonic acid isomer distribution is determined mainly by the ortho‐ and para‐directing and activating effect of the hydroxy substituent; this is also the determining factor in the aprotic sulfonations using up to 1.0 equiv of SO3. Upon using larger amounts of SO3, the sulfonation isomer distribution is increasingly determined by additional sulfonation of the corresponding phenyl hydrogen sulfate, of which the ‐OSO3H substituent is deactivating and mainly para‐ (and further ortho‐) directing. The sulfuric acid sulfonation of (2,3‐, 2,4‐ and 3,4‐dichlorophenoxy)acetic acid leads to the exclusive formation of the 4‐, 6‐ and 6‐sulfonic acid, respectively.