TABLE OF CONTENTS Aromatic carbonyl compounds are protonated in strongly acidic media, like sulfuric and chlorosulfonic acid (Equation 69).5 As a consequence, the carbonyl group exerts a powerful electron-withdrawing effect on the attached aromatic nucleus; the sulfonation of aromatic carbonyl compounds is therefore more difficult to achieve than for the parent aromatic hydrocarbons. Comparatively little work has been reported1 ,3 on the sulfonation of aryl aldehydes and none of these studies involved the use of chlorosulfonic acid.
| (69) |  |
More recent attempts to chlorosulfonate o-vanillin 215, vanillin 216 and 2,5-dimethoxybenzaldehyde with chlorosulfonic acid, under various conditions, were unsuccessful and the reactions only afforded charred products.231 In contrast, aromatic ketones of both the alkyl aryl and diaryl type have been successfully reacted with chlorosulfonic acid.1 ,3 ,5
Acetophenone 217, by mixing the excess chlorosulfonic acid in the cold followed by heating the mixture at 110 C (1 hour), gave a disulfonyl chloride which was originally considered to be the 3,5-derivative.232 However, subsequent work by Suter and Weston233 in which acetophenone 217 was treated with the reagent (10 equivalents) in carbon tetrachloride at 0 C and heated at 110 C (45 minutes) showed that the product was the 2, ?-disulfonic acid 218 (X = OH); the reaction probably involves initial sulfation of the enolic form of the ketone 217 which then rearranges to form the ?-sulfonic acid 219 (Scheme 1).
In support, acetophenone- ?-sulfonic acid
