Synthesis and herbicidal activity of acifluorfen analogues

Three series of twenty new acifluorfen analogues were designed and synthesized using methyl 2,5-dihydroxybenzoate and acifluorfen as starting materials. Their structures were characterized by ¹H NMR and ¹³C NMR. The herbicidal activities of the compounds were determined by methods of petri dish and greenhouse potted. The results showed that the herbicidal activity of compound III-02 6-methylbenzodthiazol-2-yl 5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoate against monocotyledonous weeds was significantly higher than that of acifluorfen, and its EC₅₀ values were 2.03, 0.93 μg/mL and 1.49, 0.52 μg/mL against the roots and stems of Echinochloa crusgalli and Digitaria sanguinalis, respectively. Additionally, at the dosage of 100 g a.i./ha, the efficacy of compound III -02 against monocotyledonous weeds E. crusgalli, S. sanguinalis and Setaria viridis was above 85%, which was significantly higher than that of acifluorfen, and a 100% control effect on broadleafs Portulaca oleracea, Amaranthus retroflexus and Abutilon theophrasti. The structure-activity relationship showed that the herbicidal activity of 2-NO₂ benzoyl derivatives was significantly higher than that of 2-OCH₃ analogues, and the herbicidal activity of acifluorfen benzoate derivatives against monocotyledons was significantly higher than that of benzamide derivatives.