Designing Safer Functionalized Ionic Liquids: Monoterpene-Derived Compounds for Greener Agrochemical Development

The environmental behavior and phytotoxicity of functionalized ionic liquids (FILs) featuring imidazolium cations bearing a cyclic (-)-menthol or a linear 1-decanol-derived substituent and fluorinated anions were evaluated in a soil bioassay (Raphanus sativus). Structure-activity relationships were determined by integrating measurements (water solubility, surface tension, molecular volume) with in-silico descriptors (n-octanol-water partition coefficient, log K_OW; bioconcentration factor, log BCF; asymmetry). Lipophilicity and bioaccumulation correlated with fresh-mass inhibition (EC₅₀). More-fluorinated, larger, and charge-delocalized anions were more hydrophobic, elevating bioaccumulation and toxicity. Within menthol-based series, sulfonylimide-based FILs were more phytotoxic (EC₅₀ 74.7, 107.3 mg·kg^-1 soil dry weight) than sulfonate analogues (e.g., 299.1 mg·kg^-1). FILs with linear cations were more phytotoxic and showed higher log K_OW/BCF than cyclic analogues, consistent with greater molecular volume, higher asymmetry, and reduced hydration. Antioxidant responses paralleled EC₅₀, implicating oxidative stress. This workflow improves risk assessment and provides green-by-design criteria to prioritise safer ILs.