Résumé : Heated to reflux in water containing 8 g% KOH, the herbicide diflufenican [N‐(2,4‐difluorophenyl)‐2‐[3‐(tri‐fluoromethyl)‐phenoxy]‐3‐pyridinecarboxamide, 1] was selectively transformed into 2‐[3‐(trifluoromethyl)‐phenoxy]‐3‐pyridinecarboxylic acid (2) plus 2, 4‐difluoroaniline (5); after 60 hr of heating, 27% of the initial diflufenican was transformed, yielding 21% (mole% relative to initial diflufenican) of compound 2. Heated to reflux in a mixture of acetic acid + concentrate hydrochloric acid, diflufenican was transformed into a mixture of N‐(2,4‐difluorophenyl)‐2‐hydroxy‐3‐pyridinecarboxamide (3) and 2‐hydroxy‐3‐carboxypyridine (4) plus 2,4‐difluoroaniline (5) and 3‐trifluoromethylphenol (6); after 48 hr of heating, diflufenican was completely transformed, yielding 28% (mole% relative to initial diflufenican) of compound 3, and 57% of compound 4. The base catalyzed hydrolysis thus selectively yielded compound 2; the acid catalyzed one yielded compounds 3+4: diflufenican first was transformed into compound 3, which thereafter was transformed into compound 4. Copyright © 1990 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim