Sulfuric Acid → Benzenesulfonic acid, 5-amino-2-methoxy-

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Reaction Steps

123 parts of fused p-anisidine are added dropwise over 30 minutes to 240 parts of 100% sulfuric acid, while keeping the temperature at 55°-60° C. After stirring for 15 minutes the p-anisidine is completely dissolved. This sulfuric acid solution is then run into 242 parts of 66% oleum over 30 minutes, while keeping the temperature at 30°-40° C. by cooling with an ice bath. Stirring is continued for 30 minutes at 40° C., after which time no more educt can be detected by HPLC. The batch is poured into 1000 parts of ice/water and the precipitated 4-methoxyaniline-3-sulfonic acid is filtered with suction and washed with 500 parts of ice/water, affording 179 parts of moist 97.0% 4-methoxyaniline-3-sulfonic acid, corresponding to a yield of 85%, based on p-anisidine. No more p-anisidine and no more 4-methoxyaniline-2-sulfonic acid is detectable by HPLC (<0.1%).

Provenance & Evidence