| Methyl 2-[(5-amino-2-chloro-4-fluorophenyl)thio] acetate 1 is thekey intermediate in the synthesis of fluthiacet-methyl, which is asuper-effective, wide-spectral and safe herbicide. In this paper, a newmethod of preparing this intermediate was studied:3,4-dichloro-nitrobenzene 8 as the start material, via nucleophilicsubstitution, reduction, oxidation, Schiemann reaction, oxychlorination,nitration, hydrolyzation, and nucleophilic substitution to synthesis theproduct, in 53% total yield.Bis(4-amino-2-chlorophenyl) disulfide 7 was prepared by reacting 8with the solution of sodium sulfide and sulfur and then hydroperoxide.Yield: 94.3%, purity: 99.6%.Bis(2-chloro-4-fluorophenyl) disulfide 6 was prepared by a typicalSchiemann reaction, including the diazonium tetrafluoroboric of 7prepared by diazotization with the yield of 95%, then turned into 2-chloro-4-fluorobenzenesulfonyl chloride 5 by oxychlorination withchlorine gas in conc. hydrochloric acid at 50～60℃. The total yield:69.8%, purity: 95.3%.2-Chloro-4-fluoro-5-nitrobenzenesulfonyl chloride 4 was preparedin 97.8% yield in 98% purity by nitration of 5 with 95% fuming nitricacid in conc. sulfuric acid in the existence of anhydrous sodium sulphateat 40℃for 1 hour.S-5-Acetamido-2-chloro-4-fluorophenyl ethanethioate 3 was preparedby reduction of 4 with red phosphorus and iodine in the acetic acid at thetemperature of 115～117℃for 28 hours. Yield: 92.9%, purity: 94.2%.5-Amino-2-chloro-4-fluorobenzenethiol 2 was prepared byhydrolyzation of 3 with 10% hydrochloric acid at the temperature of101℃for 2 hours. Yield: 98.7%, purity: 94.7%.Methyl 2-[(5-amino-2-chloro-4-fluorophenyl)thio] acetate 1 wasprepared by nucleophilic substitution of 2 with methyl 2-chloroacetateat the room temperature in the condition of dry dichloroethane as solventand triethylamine for 1 hour. Yield: 91.9%, purity: 92.1%.In conclusion, the process has advantages in simple operation, goodyield, high purity and little waste, which are industrially valuable. |
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