Synthesis of tritiated derivatives of the diphenylether herbicides acifluorfen and acifluorfen methyl

Acifluorfen 1 and acifluorfen methyl 2, two herbicides of the diphenylether family, are inhibitors of protoporphyrinogen oxidases. Two tritiated derivatives of these compounds, namely 3‐[3H]‐5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid [3H]‐1, and methyl 3‐[3H]‐5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid [3H]‐2, have been synthesised from 3‐[3H]‐5‐hydroxybenzoic acid, in order to probe their interactions with the target enzymes.