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.