On the Synthesis of Sulfonated Derivatives of 2,3‐Dimethylaniline and 3,4‐Dimethylaniline
Baking the hydrogensulfate salt of 2,3‐dimethylaniline (1) or of 3,4‐dimethylaniline (2) led to 4‐amino‐2,3‐dimethylbenzenesulfonic acid (4) and 2‐amino‐4,5‐dimethylbenzenesulfonic acid (5), respectively (Scheme 1). The sulfonic acid 5 was also obtained by treatment of 2 with sulfuric acid or by reaction of 2 with amidosulfuric acid. 3‐Amino‐4,5‐dimethylbenzenesulfonic acid (3) and 5‐Amino‐2,3‐dimethylbenzenesulfonic acid (6) were prepared by sulfonation of 1,2‐dimethyl‐3‐nitrobenzene (9) to 3,4‐dimethyl‐5‐nitrobenzenesulfonic acid (11) and of 1,2‐dimethyl‐4‐nitrobenzene (10) to 2,3‐dimethyl‐5‐nitrobenzenesulfonic acid (12), respectively, with subsequent Béchamp reduction (Scheme 1). Preparations of 2‐amino‐3,4‐dimethylbenzenesulfonic acid (7) and of 6‐amino‐2,3‐dimethylbenzenesulfonic acid (8) were achieved by the sulfur dioxide treatment of the diazonium chlorides derived from 3,4‐dimethyl‐2‐nitroaniline (24) and from 2,3‐dimethyl‐6‐nitroaniline (31) to 3,4‐dimethyl‐2‐nitrobenzenesulfonyl chloride (29) and 2,3‐dimethyl‐6‐nitrobenzenesulfonyl chloride (32), respectively, followed by hydrolysis to 3,4‐dimethyl‐2‐nitrobenzenesulfonic acid (30) and 2,3‐dimethyl‐6‐nitrobenzenesulfonic acid (33), and final reduction (Scheme 3). Compound 7 was also synthesized by reaction of 4‐chloro‐2,3‐dimethylaniline (23) with amidosulfuric acid to 2‐amino‐5‐chloro‐3,4‐dimethylbenzenesulfonic acid (20) and subsequent hydrogenolysis (Scheme 2). 4′‐Bromo‐2′, 3′‐dimethyl‐acetanilide (13) and 4′‐chloro‐2′, 3′‐dimethyl‐acetanilide (14) on treatment with oleum yielded 5‐acetylamino‐2‐bromo‐3,4‐dimethylbenzenesulfonic acid (17) and 5‐acetylamino‐2‐chloro‐3,4‐dimethylbenzenesulfonic acid (18), respectively. Their structures were proven by hydrolysis to 5‐amino‐2‐bromo‐3,4‐dimethylbenzenesulfonic acid (21) and 5‐amino‐2‐chloro‐3,4‐dimethylbenzenesulfonic acid (22), followed by reductive dehalogenation to 3.