Sulfuric Acid → 5-Amino-2-methylbenzenesulfonic acid

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Reaction Steps

107 parts of fused p-toluidine are added dropwise over 30 minutes to 183 parts of 100% sulfuric acid, while keeping the temperature at 75°-80° C. After stirring for 15 minutes the p-toluidine is completely dissolved. This sulfuric acid solution is then run into 260 parts of 66% oleum over 30 minutes, while keeping the temperature at 40°-50° C. by cooling with an ice bath. Stirring is continued for 30 minutes at 45°-50° C., after which time no more educt can be detected by HPLC. The batch is poured into 500 parts of ice/water and the precipitated 4-methylaniline-3-sulfonic acid is filtered with suction and washed with 500 parts of ice/water, affording 248 parts of moist 70.0% 4-methylaniline-3-sulfonic acid, corresponding to a yield of 93%, based on p-toluidine. No more p-toluidine and no more 4-methylaniline-2-sulfonic acid is detectable by HPLC (<0.1%).

Provenance & Evidence