Diphenylamine, reaction with chlorosulfonic acid

Diphenylamine 327 reacts with chlorosulfonic acid in nitrobenzene < 90 C the initial product is the amine chlorosulfate which at higher temperatures decomposes to yield the 4-sulfonic acid and/or 4,4 - disulfonic acid depending on the ratio of reagent to substrate used. However, attempts to prepare diphenyla-mine-4,4 -disulfonyl chloride by reaction of diphenylamine with excess chlorosulfonic acid (five equivalents) in thionyl chloride were unsuccessful. The product appeared to be a complex mixture of polychloro derivatives of phenothiazine. On the other hand, reaction of diphenylamine 327 with a large excess of the reagent (12 equivalents) at 100 °C (1 hour) gave the 2,2, 4,4 -tetrasulfonylchloride (328, 72%) (Scheme 10). 

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