Reaction #465955

Reaction equation

NaOH

4-amino-3,5,6-trichloropyridine-2-carboxylic acid

→

4-Amino-3,6-dichloropyridine-2-carboxylic Acid

Solvents

water

Conditions

Workup

1. 1
   Filtrationfiltered through a paper
2. 2
   Filtrationfilter
3. 3
   Othera temperature of 30° C.
4. 4
   Temperatureto maintain
5. 5
   Concentrationthe NaOH concentration at a 1.5 to 2.0 percent excess
6. 6
   workup.WAITAfter about 15 hours (hr)
7. 7
   Otherthe electrolysis was terminated
8. 8
   Filtrationthe cell effluent was filtered through a paper
9. 9
   Filtrationfilter
10. 10
    Concentrationconcentrated to about 750 g of crude
11. 11
    Concentrationconcentrate
12. 12
    workup.STIRRINGwith stirring
13. 13
    Otherover 30 min
14. 14
    TemperatureThe resulting slurry was cooled to ambient temperature
15. 15
    Filtrationfiltered
16. 16
    WashThe filter cake was washed with 3×200 milliliter (mL) portions of water
17. 17
    Otherdried under vacuum at 80° C

Procedure

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).

Source