Third-generation ionic liquids with N-alkylated 1,4-diazabicyclo[2.2.2]octane cations and pelargonate anions†
Ionic liquids that belong to the third-generation designs due to their intended biological activity are compounds with high potential applications as plant-protection products. The present study describes the synthesis and characterization of novel ionic liquids with cations based on the alkyl derivatives of 1,4-diazabicyclo[2.2.2]octane (DABCO) and an anion derived from naturally occurring pelargonic acid. The developed synthesis method allowed obtaining products with a high yield (≥96%), and the liquids were characterized as high-viscosity liquids at room temperature. This allowed classifying the products as ionic liquids (ILs). The structures of the obtained ILs were confirmed on the basis of their NMR and IR spectra as well as by elemental analysis. All the products exhibited surface activity and were capable of partially wetting a hydrophobic surface. The tested ionic liquids exhibited higher herbicidal activity against winter oilseed rape (Brassica napus L.) and common lambsquarters (Chenopodium album L.) at a lower dose compared to a commercial preparation in greenhouse studies. The studied ionic liquids also exhibited different effects as antifeedants on various insect species. The best results were obtained against beetles belonging to the granary weevil species (Sitophilus granarius L.). The relation between the surface-tension-reduction efficiency pC20 and biological activity was investigated. The herbicidal activity was also correlated with the value of the contact angles for the studied pelargonates. All the obtained results indicate that the designed and synthesized ionic liquids possess double biological functions: herbicidal activity and deterrent activity.