Reaction CXLIX.—Intramolecular Rearrangement of Aromatic Amine Sulphates

Reaction CXLIX. Intramolecular Rearrangement of Aromatic Amine Sulphates.—When sulphuric acid is added to an amine a sulphate is usually formed. If the sulphate is heated either alone (baking process) or with 

Sulphonic acids can be made by the baking process, which are difficult to make in the ordinary way, e.g., 

In the baking process much less sulphuric acid is required. For new method of eliminating water, see E.P., 354,201. 

Preparation 293.—Sulphanilic Acid (l-Amino-A-benzenesuIphonic Acid). 

Method I.—20 gms. of aniline are gradually added to 65 gms. of cone, sulphuric acid placed in a round-bottomed flask. Much heat is developed, and the contents of the flask should be cooled when the aniline is being added. The flask which contains aniline sulphate and excess cone, sulphuric acid is now heated on an oil or paraffin bath to 185° for about 5 hours. When a test portion, treated with dilute caustic soda solution, liberates no free aniline, the sulphonation is complete. The contents of the flask, after cooling, are poured into cold water, when the sulphanilic acid separates, usually as discoloured crystals. These are filtered off and recrystallised from water, adding a little animal charcoal, if necessary. A further crop can be obtained from the mother liquor. 

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