Dicamba
is a widely applied herbicide for crop protection and has
potential for volatility. New formulations containing dicamba with
greatly reduced volatility, introduced to the market in 2017, still
caused foliar injury to crops and other plants in Arkansas and neighboring
states in the United States. In response, we proposed the transformation
of dicamba into protic as well as aprotic dicamba-based organic salts
called herbicidal ionic liquids (HILs). All of the HILs were characterized
by high stability, whereas the biological activity of the most effective
products, evaluated during greenhouse studies, was found to be greater
than that of currently used commercial analogues. Furthermore, the
possibility of introducing an alkyl chain of a specific length allows
one to obtain plant protection products with the desired physicochemical
properties while maintaining herbicidal effectiveness. These studies
are expected to aid in the design and development of new herbicidal
formulations, which, depending on the weed species, could increase
the efficacy of the applied active ingredient. Simultaneously, the
volatility of the synthesized compounds, particularly those containing
quaternary ammonium cations, was multiple times lower than that of
the free acid of dicamba. This strategy minimizes the risk of off-site
movement via volatilization, which may cause significant damage to
neighboring broadleaf crops and pose a threat to existing ecosystems.
In this study, two homologous series of novel herbicidal ionic liquids (HILs) were synthesized in a simple metathesis reaction between alkyl[2‐(2‐hydroxyethoxy)ethyl]dimethylammonium bromides and alkali metal salts of 4‐chloro‐2‐methylphenoxyacetic acid (MCPA) or 3,6‐dichloro‐2‐methoxybenzoic acid (dicamba), known as popular herbicides from the class of growth regulators. These HILs were subsequently mixed to prepare double‐salt herbicidal ionic liquids (DSHILs). The DSHILs were characterized by substantially altered parameters of viscosity, refractive index, glass transition temperatures and surface activity compared to the average values expected for ideal mixtures of their individual components (HILs). Interestingly, DSHILs possessed superior physicochemical properties such as relatively low viscosity or facilitated formation of micelles, which emphasizes the complex nature of multi‐ion interactions in the microstructures of ionic liquid mixtures. The biological tests showed improved efficiency of DSHILs against tested weeds compared to the reference herbicides and parent HILs.
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