TABLE OF CONTENTS The (-I) inductive effect of the halogen atom means that halobenzenes are less easily sulfonated than benzene, and due to steric factors, the halogen atom tends to strongly direct the sulfonation to the p-position.1 ,2 Huntress and Carten95 introduced chlorosulfonic acid as a reagent for the identification of aryl halides either by reaction with neat excess chlorosulfonic acid or in the presence of chloroform as an inert solvent. In the majority of cases, the aryl halides were converted into the corresponding sulfonyl chlorides in good yields and these were subsequently treated with ammonium hydroxide to give the sulfonamides, the melting points of which were used in organic qualitative analysis to identify the original aryl halides.
Some compounds gave abnormal results:95 thus fluorobenzene with neat chlorosulfonic acid (40 C) only gave 4,4'-difluorodiphenyl sulfone. On the other hand, treatment of fluorobenzene with the reagent in chloroform solution afforded some p-fluorobenzenesulfonyl chloride;96 while m-difluorobenzene reacted with excess reagent (30 40 C, 3 hours) to give 2,4-difluorobenzenesulfonyl chloride (98.6% yield).97
Chlorobenzene reacts with an equimolar amount of chlorosulfonic acid to give mainly the p-sulfonic acid together with a little of the sulfonyl chloride and the sulfone.1 With an excess of the reagent good yields of p-chlorobenzenesulfonyl chloride are obtained.2 ,95 The kinetics of the sulfonation of chlorobenzene with chlorosulfonic acid have been studied,98 and the reaction has been reported in several patents. 99 103 These involved various modifications such as the use of...
