Process of preparing 1,1'-disulfandiylbis(4-fluoro-2-methyl-5-nitrobenzol)

A process for preparing 1,1′-disulfanediylbis(4-fluoro-2-methyl-5-nitrobenzene) of formula (I)

• comprising
• (1) reacting, 3-fluorotoluene with chlorosulfonic acid to give a first mixture comprising 4-fluoro-2-methylbenzenesulfonyl chloride of formula (IX) and 2-fluoro-4-methylbenzenesulfonyl chloride of formula (X),
• (2) nitrating, the first mixture from (1) with nitric acid to give a second mixture comprising 4-fluoro-2-methyl-5-nitrobenzenesulfonyl chloride of formula (III), 4-fluoro-2-methyl-3-nitrobenzenesulfonyl chloride of formula (XI) and 2-fluoro-4-methyl-5-nitrobenzenesulfonyl chloride of formula (XII),
• (3), converting the second mixture from (2) to a third mixture by reducing the amount of 4-fluoro-2-methyl-3-nitrobenzenesulfonyl chloride of formula (XI) by at least 50%, based on the starting amount of 4-fluoro-2-methyl-3-benzenesulfonyl chloride of formula (XI) in the second mixture,
• (4), reducing the third mixture from (3) to give a fourth mixture, comprising 1,1′-disulfanediylbis(4-fluoro-2-methyl-5-nitrobenzene) of formula (I) and at least one further compound (A) selected from
• 1,1′-disulfanediylbis(4-fluoro-2-methyl-3-nitrobenzene) of formula (XIII),
• 1,1′-disulfanediylbis(2-fluoro-4-methyl-5-nitrobenzene) of formula (XIV),
• 1-fluoro-4-[(4-fluoro-2-methyl-5-nitrophenyl)disulfanyl]-3-methyl-2-nitrobenzene of formula (XV),
• 1 -fluoro-4-[(2-fluoro-4-methyl-5-nitrophenyl)disulfanyl]-5-methyl-2-nitrobenzene of formula (XVI),
• and
• 1 -fluoro-4-[(2-fluoro-4-methyl-5-nitrophenyl)disulfanyl]-3-methyl-2-nitrobenzene of formula (XVII).