Some comments on the syntheses of 5‐amino‐m‐xylene‐2‐sulfonic acid and 5‐amino‐m‐xylene‐4‐sulfonic acid
Treatment of 5‐amino‐m‐xylene (1) with oleum led to a 55:45 mixture of 5‐amino‐m‐xylene‐2‐sulfonic acid (2) and 5‐amino‐m‐xylene‐4‐sulfonic acid (3). The structure of both isomers was proven by reaction of sulfur dioxide with the diazonium chlorides derived from 2‐amino‐5‐nitro‐m‐xylene (5) and 4‐amino‐5‐nitro‐m‐xylene (8) giving 5‐nitro‐m‐xylene‐2‐sulfonyl chloride (6) and 5‐nitro‐m‐xylene‐4‐sulfonyl chloride (9) respectively, followed by hydrolyses to the corresponding sulfonic acids 7 and 10, and final Béchamp reductions. The sulfonic acid 2 was also prepared by sulfonation of 5‐acetylamino‐m‐xylene (4) to 5‐acetylamino‐m‐xylene‐2‐sulfonic acid (11) and subsequent hydrolysis. A further procedure for the synthesis of 3 was sulfonation of 5‐amino‐2‐chloro‐m‐xylene (12) – prepared by Béchamp reduction of 2‐chloro‐5‐nitro‐m‐xylene (13) – or of 5‐amino‐2‐bromo‐m‐xylene (15) – prepared by bromination of 4 and subsequent hydrolysis – to 5‐amino‐2‐chloro‐m‐xylene‐4‐sulfonic acid (16) and 5‐amino‐2‐bromo‐m‐xylene‐4‐sulfonic acid (17) respectively, followed by hydrogenolysis.