Amines chlorosulfates

In the first case (22), almost stoichiometric amounts of sulfuric acid or chlorosulfonic acid are used. The amine sulfate or the amine chlorosulfate is, first, formed and heated to about 180 or 130°C, respectively, to rearrange the salt. The introduction of the sulfonic acid group occurs only in the ortho position, and an almost quantitative amount of l-aminoanthraquinone-2-sulfonic acid is obtained. On the other hand, the use of oleum (23) requires a large excess of SO to complete the reaction, and inevitably produces over-sulfonated compound such as l-amino-anthraquinone-2,4-disulfonic acid. Addition of sodium sulfate reduces the byproduct to a certain extent. Improved processes have been proposed to make the isolation of the intermediate (19) uimecessary (24,25). 

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). 

Electron-deficient as well as electron-rich aryl boronic acids proved to be competent partners in the reaction, but electron-deficient boronic acids required higher temperatures. Boronic acids containing aryl halides (I, Cl) were also competent partners, providing a functional handle for further elaboration. Both primary and secondary amines have been utilised as coupling partners. A limitation of this chemistry is the inability to use nitrogen-based heterocycles due to either protodeboronation or the instability of the electron-poor sulfonyl chloride intermediate. Buchwald and coworkers later found that pyridylzinc reagents could be coupled with 2,4,6-trichlorophenyl chlorosulfate (TCPC) to access pyridine sulfonates without a transition metal catalyst." The pyridine sulfonates were subsequently treated with amines to generate sulfonamides. 

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