Abstract

This chapter deals with the direct replacement of the hydrogen atoms in aromatic hydrocarbons, and their halogen derivatives by sulfonic acid, sulfonyl chloride, and sulfonyl fluoride groups. These sulfonations are more convenient and much more commonly used than indirect synthetic methods such as those that involve the reaction of an aryl halide with a sulfite, the oxidation of a disulfide, thiol, or sulfinic acid, or the conversion of a diazonium salt into a sulfonic acid. The reagents most used for direct sulfonation are sulfuric acid, sulfur trioxide in an inert solvent, in sulfuric as oleum, or an addition product with pyridine or dioxane, Chlorosulfonic acid, its salts and its anhydride and flurosulfonic acid. Combinations of reagents have been used.