Benzils and other Diketones

In the modified reaction mechanism,the chlorohydrin intermediate 260 is sulfonated and in this molecule the deactivation of the phenyl nucleus towards electrophilic attack is significantly reduced. The chlorohydrin moiety provides the appropriate reactivity, directs the orientation of chlorosulfonation and allows the reaction to proceed under comparatively mild conditions. 

In contrast, 3-thienylbenzil with chlorosulfonic acid-thionyl chloride, gave a mixture of isomers these results are in accord with the predicted reaction mechanism.  

4- Diaminoanthraquinone was treated with chlorosulfonic acid (1.03 equivalents) in o-dichlorobenzene over 1 hour at 30 C. The mixture was heated at 70 °C and more of the reagent (1.1 equivalents) was added. After further heating at 115-120 °C (10 hours), the reaction afforded, as expected, the 2-sulfonic acid (95% yield).2  

5- Di (2-methoxyanilino) anthraqinone, by treatment with a large excess of chlorosulfonic acid (17 equivalents) at 40-45 °C (1 hour), gave the 5-chlorosulfo-nyl derivative.  

The diketones (263 n = 1, 2) by treatment with chlorosulfonic acid rearranged to form the chlorosulfite 264 (64% yield) (Equation 83).  

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