Synthesis, acaricidal activity, and structure–activity relationships of novel phenyl trifluoroethyl thioether derivatives containing substituted benzyl groups

Abstract BACKGROUND To discover and develop novel acaricidal compounds, a series of 2‐fluoro‐4‐methyl/chlorine‐5‐((2,2,2‐trifluoroethyl)thio)aniline/phenol compounds containing N/O‐benzyl moieties were synthesized based on lead compound LZ‐1 . RESULTS The activity of these compounds against carmine spider mites ( Tetranychus cinnabarinus ) was determined using the leaf‐spray method. Bioassays indicated that most of the designed target compounds possessed moderate to excellent acaricidal activity against adult T. cinnabarinus . The median lethal concentrations of 25b and 26b were 0.683 and 2.448 mg L −1 against adult mites, respectively; exceeding those of bifenazate (7.519 mg L −1 ) and lead compound LZ‐1 (3.658 mg L −1 ). Compound 25b exhibited 100% mortality in T. cinnabarinus larvae at 10 mg L −1 . CONCLUSION Continuing the study of these compounds in field trials, we compared the efficacy of mite killing by compound 25b with the commercial pesticide spirodiclofen and showed that mite control achieved 95.9% and 83.0% lethality at 10 and 22 days post‐treatment. In comparison, spirodiclofen showed 92.7% lethality at 10 days and 77.2% lethality at 22 days post‐treatment at a concentration of 100 mg L −1 . Results showed that 25b produced more facile and long‐lasting control against T. cinnabarinus than the commercial acaricide spirodiclofen. Density functional theory analysis and electrostatic potential calculations of various molecular substitutions suggested some useful models to achieve other highly active miticidal compounds. © 2023 Society of Chemical Industry.