Zur Synthese sulfonierter Derivate von 2‐Fluoranilin

Syntheses of Sulfonated Derivatives of 2‐Fluoroaniline Synthesis of 4‐amino‐3‐fluorobenzenesulfonic acid (3) was achieved in two ways: reaction of 2‐fluoroaniline (1) with amidosulfonic acid and by first conventionally converting 4‐nitro‐3‐fluoroaniline (8) to 4‐nitro‐3‐fluorobenzenesulfonyl chloride (9) followed subsequently by hydrolysis to 3‐fluoro‐4‐nitrobenzenesulfonic acid (10) and reduction. Hydrogenolysis of 3 gave sulfanilic acid (7). Both, sulfonation of fluorobenzene (6) to 4‐fluorobenzenesulfonic acid (11) followed by nitration and sulfonation of 1‐fluoro‐2‐nitrobenzene (12) led to 4‐fluoro‐3‐nitrobenzenesulfonic acid (13). Reduction of 13 gave the isomeric 3‐amino‐4‐fluorobenzenesulfonic acid (4), which was also obtained both by sulfonation of 1 and by sulfonation of o‐fluoroacetanilide (14) followed by hydrolysis. Selective hydrogenolyses of 2‐amino‐5‐bromo‐3‐fluorobenzenesulfonic acid (15), prepared by reaction of 4‐bromo‐2‐fluoroaniline (16) with amidosulfonic acid, and of 4‐amino‐2‐bromo‐5‐fluorobenzenesulfonic acid (20), obtained by sulfonation of 5‐bromo‐2‐fluoroaniline (19) yielded the isomers 2‐amino‐3‐fluorobenzenesulfonic acid (5) and 3, respectively. The fourth isomer, 3‐amino‐2‐fluorobenzenesulfonic acid (2), was synthesized by sulfur dioxide treatment of the diazonium chloride derived from 2‐fluoro‐3‐nitroaniline (21) to 2‐fluoro‐3‐nitrobenzenesulfonyl chloride (22), followed by hydrolysis to 2‐fluoro‐3‐nitrobenzenesulfonic acid (23) and final Béchamp‐reduction.