TABLE OF CONTENTS Chlorosulfonic acid, although primarily used in the sulfonation/chlorosulfonation of organic compounds, also participates in several other important reactions as briefly mentioned in the introduction (Chapter 1, p 5). Examples of these miscellaneous reactions include: (1) halogenation; (2) cyclization; (3) alkylation; (4) polymerization; (5) condensation (in which the reagent acts as an acidic dehydrating agent, including its use in esterification); (6) isomerization and rearrangements; (7) other reactions.
In this discussion, reference is made to other chapters in the book, which mention many of the reactions and give literature references which are therefore not reported here.
Chlorosulfonic acid may function as a chlorinating agent for aromatic substrates at high temperatures, thus p-dichlorobenzene, by heating with excess of the reagent at 140 C, yields 1,2,4,5-tetrachlorobenzene while at higher temperatures (210 220 C), the reaction gives hexachlorobenzene (Chapter 6, ref. 13). These high temperature chlorinations are probably homolytic reactions.
The presence of iodine is known to catalyse the chlorination of organic compounds by Chlorosulfonic acid, enabling the reaction to proceed under comparatively mild conditions. So chlorination is a feature of the attempted sulfonation of aromatic iodo compounds with chlorosulfonic acid (see Chapter 2, p 19); for instance, reaction of p-diiodobenzene with excess reagent (five equivalents) at 50 C yields tetrachlorodiiodobenzene (82%), (Chapter 6, ref. 13). The chlorination is catalysed by traces of iodine and the reaction under these conditions probably involves both homolytic and heterolytic steps (see Chapter 4, p 49). Hexachloro- p-xylene, by treatment with a mixture of...
