“Sweet” ionic liquids comprising the acesulfame anion – synthesis, physicochemical properties and antifeedant activity towards stored product insects

Abstract

Ionic liquids (ILs) are known to be useful as agrochemicals; however, their activity strongly depends on the structure of the selected cations and anions. This study is focused on the utilization of acesulfame K, a sweetener commonly used in the food industry, in the synthesis of ILs, their characterization and their application as feeding deterrents (antifeedants) against stored product insects. A new homologous series of “sweet” ILs containing cations functionalized with a diglycol [2-(2-hydroxyethoxy)ethyl] group and an acesulfame anion were obtained with high yields under mild conditions via a two-step process. Subsequently, the influence of the length of the alkyl chain (ranging from ethyl to hexadecyl) in the cations of the functionalized ILs on their various physicochemical properties (phase transitions, thermal stability, density, viscosity, refractive index, solubility and octanol–water partition coefficient) was thoroughly evaluated. The octanol–water partition coefficient values indicate low potential of the obtained products for bioaccumulation in the environment and for leaching into groundwater. Additionally, the synthesized ILs were examined in terms of their antifeedant activity towards widespread stored product pests: the granary weevil, rice weevil, confused flour beetle and khapra beetle. All the obtained ILs exhibited biological activity, and the highest efficacy against tested insects was demonstrated by products comprising long alkyls (tetradecyl and hexadecyl). Additionally, it was established that these ILs were also characterized by the highest octanol–water partition coefficient values. The obtained “sweet” ILs with “designer” physicochemical properties and promising biological activity results exhibit potential for use in the storage of crop protection products.