反应详情

温度

85 °C

In a 3-liter (L) beaker was added 2000 grams (g) of hot water, 115.1 g of 50 percent by weight NaOH, and 200 g of wet 4-amino-3,5,6-trichloropyridine-2-carboxylic acid (79.4 percent). The solution was stirred for 30 minutes (min), filtered through a paper filter, and transferred to a 5-L feed/recirculation tank. This solution weighed 2315 g and contained 6.8 percent 4-amino-3,5,6-trichloropyridine-2-carboxylic acid. This feed was recirculated at a rate of about 9.46 L/min and a temperature of 30° C. through an undivided electrochemical cell having a Hastelloy C anode and an expanded silver mesh screen cathode. After normal anodization at +0.7 volt (v), the polarity of the cell was reversed and the electrolysis was started. The cathode working potential was controlled at −1.1 to −1.4 v relative to an Ag/AgCl (3.0 M Cl−) reference electrode. While recirculating the feed, a solution of 50 percent NaOH is slowly pumped into the recirculation tank to maintain the NaOH concentration at a 1.5 to 2.0 percent excess. After about 15 hours (hr), the electrolysis was terminated and the cell effluent was filtered through a paper filter. The solution was neutralized with concentrated HCl and concentrated to about 750 g of crude concentrate. The concentrate was warmed to 85° C. with stirring and the pH was adjusted to less than 1 with concentrated HCl over 30 min. The resulting slurry was cooled to ambient temperature and filtered. The filter cake was washed with 3×200 milliliter (mL) portions of water and dried under vacuum at 80° C. The dried product, 118.1 g assayed at 90.6 percent desired product; gas chromatography (GC) indicated about 4 percent 4-amino-3,5,6-trichloropyridine-2-carboxylic acid remaining as an impurity. A purified sample of 4-amino-3,6-dichloropyridine-2-carboxylic acid had a melting point (mp) of 185-187° C. (dec.); 1H NMR (DMSO-d6): δ 13.9 (br, 1H), 7.0 (br m, 2H), 6.8 (s,1H); 13C NMR {1H} (DMSO-d6): δ 165.4 (1C), 153.4 (1C), 149.5 (1C), 147.7 (1C), 111.0 (1C), 108.1 (1C).

1. filtrationfiltered through a paper
2. filtrationfilter
3. customa temperature of 30° C.
4. temperatureto maintain
5. concentrationthe NaOH concentration at a 1.5 to 2.0 percent excess
6. waitAfter about 15 hours (hr)
7. customthe electrolysis was terminated
8. filtrationthe cell effluent was filtered through a paper
9. filtrationfilter
10. concentrationconcentrated to about 750 g of crude
11. concentrationconcentrate
12. stirringwith stirring
13. customover 30 min
14. temperatureThe resulting slurry was cooled to ambient temperature
15. filtrationfiltered
16. washThe filter cake was washed with 3×200 milliliter (mL) portions of water
17. customdried under vacuum at 80° C