Synthesis of stable isotopes of auxinic herbicides 4-amino-3,5,6-trichloropicolinic acid and 4-amino-3,6-dichloropicolinic acid

✍ Scribed by Peter L. Johnson; Norman R. Pearson; Bert Schuster; Jeremy Cobb

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: French
• Weight: 203 KB
• Volume: 52
• Category: Article
• ISSN: 0022-2135
• DOI: 10.1002/jlcr.1613

✦ Synopsis

Abstract

Pentachloropyridine serves as a key intermediate in the synthesis of 4‐amino‐3,5,6‐trichloropicolinic acid (picloram) and 4‐amino‐3,6‐dichloropicolinic acid (aminopyralid). An M+3 stable isotope of pentachloropyridine (1, pentachloropyridine‐1‐^15^N‐2,6‐^13^C~2~) was prepared from K^13^C^15^N. Isotopically labeled pentachloropyridine was then carried through a seven‐step synthesis to give an M+3 stable isotope of 4‐amino‐3,5,6‐trichloropicolinic acid (2, picloram‐1‐^15^N‐2,6‐^13^C~2~) in an overall yield of 42%. The chlorine atom in the 5‐position of 2 was selectively removed via electrochemical reduction. Carrying out the electrochemical reduction in water provided an M+3 stable isotope of 4‐amino‐3,6‐dichloropicolinic acid (3, aminopyralid‐1‐^15^N‐2,6‐^13^C~2~), whereas conducting the reduction in deuterium oxide produced an M+4 stable isotope (4, aminopyralid‐1‐^15^N‐2,6‐^13^C~2~‐5‐^2^H). Copyright © 2009 John Wiley & Sons, Ltd.