Sulfuric Acid → 6-Chlorometanilic acid

Participants

Reaction Conditions

Reaction Steps

128 parts of p-chloroaniline are added, in portions, at a maximum temperature of 85° C. to 238 parts of 100% sulfuric acid. The mixture is then stirred for 15 minutes at 65° C. until a clear solution forms. This sulfuric acid solution is run into 420 parts of 66% oleum over 30 minutes, while keeping the temperature at 65°-70° C. by cooling with an ice bath. The reaction mixture is stirred for 2 hours at 70° C. to bring the reaction to completion and to give 4-chloroaniline-3-sulfonic acid. The batch is then heated to 160° C. and stirred for 3 hours at this temperature. After cooling to 50° C., the sulfonation mixture is poured into 1100 parts of ice/water, and the resulting clear solution is partially neutralised with 400 parts of a 50% solution of potassium hydroxide. The monopotassium salt of 4-chloroaniline-2,5-disulfonic acid slowly precipitates and is filtered with suction and dried under vacuum, affording 260 parts of 62.0% 4-chloroaniline-2,5-disulfonic acid, corresponding to a yield of 56%, based on p-chloroaniline. The purity is >97% (analysis by HPLC).

Provenance & Evidence