Syntheses of Sulfonated Derivatives of 4‐Amino‐1, 3‐dimethylbenzene and 2‐Amino‐1, 3‐dimethylbenzene
Direct sulfonation of 4‐amino‐1, 3‐dimethylbenzene (1) and sulfonation of 4‐nitro‐1,3‐dimethylbenzene (4) to 4‐nitro‐1,3‐dimethylbenzene‐6‐sulfonic acid (3) followed by reduction yield 4‐amino‐1,3‐dimethylbenzene‐6‐sulfonic acid (2). The isomeric 5‐sulfonic acid (5) however is prepared solely by baking the acid sulfate salt of 1. Reaction of sulfur dioxide with the diazonium chloride derived from 2‐amino‐4‐nitro‐1,3‐dimethylbenzene (7) leads to 4‐nitro‐1,3‐dimethylbenzene‐2‐sulfonyl chloride (8), which is successively hydrolyzed to 4‐nitro‐1,3‐dimethylbenzene‐2‐sulfonic acid (9) and reduced to 4‐amino‐1, 3‐dimethylbenzene‐2‐sulfonic acid (6). Treatment of 4‐amino‐6‐bromo‐1,3‐dimethylbenzene (12) and 4‐amino‐6‐chloro‐1, 3‐dimethylbenzene (13), the former obtained by reduction of 4‐chloro‐6‐nitro‐1,3‐dimethyl‐benzene (10) and the latter from 4‐chloro‐6‐nitro‐1, 3‐dimethylbenzene (11), with oleum yield 4‐amino‐6‐bromo‐1,3‐dimethylbenzene‐2‐sulfonic acid (14) and 4‐amino‐6‐chloro‐1,3‐dimethylbenzene‐2‐sulfonic acid (15) respectively; subsequent carbon‐halogen hydrogenolyses of 14 and 15 lead also to 6 (Scheme 1).
Baking the acid sulfate salt of 2‐amino‐1, 3‐dimethylbenzene (17) gives 2‐amino‐1, 3‐dimethylbenzene‐5‐sulfonic acid (16), whereas the isomeric 4‐sulfonic acid (18) can be prepared by either of the following three possible pathways: Sulfonation of 2‐nitro‐1,3‐dimethylbenzene (20) to 2‐nitro‐1,3‐dimethylbenzene‐4‐sulfonic acid (21) followed by reduction or sulfonation of 2‐acetylamino‐1,3‐dimethylbenzene (19) to 2‐acetylamino‐1,3‐dimethylbenzene‐4‐sulfonic acid (22) with subsequent hydrolysis or direct sulfonation of 17. Further sulfonation of 18 yields 2‐amino 1,3‐dimethylbenzene‐4,6‐disulfonic acid (23), the structure of which is independently confirmed by reduction of unequivocally prepared 2‐nitro‐ 1,:3‐dimethylbenzene‐4,6‐disulfonic acid (24)(Scheme 2).