Syntheses of Sulfonated Derivatives of 2-Fluoroaniline

Article abstract of DOI:10.1002/hlca.19830660108

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 Bechamp-reduction.