Xiao-hua Du, Sheng Chen, Mei-Ru Zheng
Dec 1, 2005
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Influential Citations
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Journal
Organic Preparations and Procedures International
Abstract
2-Chloro-4-fluoro-5-nitrobenzenesulfonyl chloride (4) is useful in the synthesis of the key intermediate methyl 5-amino-2-chloro-4-fl~orophenylthioacetate,~ which is in turn utilized for the preparation of pesticides such as the herbicidal j7uthiacet-methyL2 Kojima et aL3 prepared 4 in 78% yield by chlorosulfonation of 4-chloro-2-fluoronitrobenzene with chlorosulfonic acid. Since 4-chloro-2-fluoronitrobenzene is very expensive and difficult to prepare," an alternate route to 4 was sought. Accordingly, we report the synthesis of 4 from bis(4-amino-2chlorophenyl) disulfide (1) using the Schiemann reaction, oxychlorination, and nitration as shown in Scheme. The starting material 1 had previously been prepared from 3,4-dichloronitrobenzene. As shown in Scheme, bis(2-chloro-4-fluorophenyl) disulfide (2) was prepared by a typical Schiemann reaction (step a ) , including diazotization with sodium nitrite in acidic conditions (20% sulfuric acid was an optimized medium for this reaction), precipitation with tetrafluoroboric acid and pyrolysis of the precipitated diazonium tetrafluoroborate. The diazonium tetrafluoroborate of 1 was pyrolyzed smoothly in o-dichlorobenzene at 130140°C give 2 i n 65-75%. In comparison, 2 was prepared6 from 2-chloro-4-fluoroaniline in 24% yield, comprising diazotization, sulfurization, hydrolysis and oxidization. In step b, 2-chloro-4-fluorobenzenesulfonyl chloride (3) was prepared in better than 90% yield by oxychlorination of 2 with chlorine gas in conc. hydrochloric acid at 50-60°C. HzNq qNHz 2 '9gF -b s-s 72% ' s-s 91% CI CI CI 2 CI