Zur Synthese sulfonierter Derivate von 4‐Amino‐1,3‐dimethylbenzol und 2‐Amino‐1,3‐dimethylbenzol

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).