Dicamba-Based Herbicides: Herbicidal Ionic Liquids versus Commercial Forms

Abstract

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.

Herbicidal Ionic Liquids: A Promising Future for Old Herbicides? Review on Synthesis, Toxicity, Biodegradation, and Efficacy Studies

“… 41 Using this approach, tebuconazole- and propiconazole-based ILs with MCPA, MCPP, 2,4-D, and dicamba as anions can be obtained. 40 Furthermore, protic HILs originating from primary, secondary, and tertiary amines or heterocyclic compounds with tertiary nitrogen atom (e.g., 1-methylimidazole, isoquinoline) may be synthesized using this method, with clopyralid, 27 dicamba, 39 bromoxynil, 23 2,4-D, 41 picloram, 28 mesotrione, 38 2,2′-thioacetate, and 2,2′-thiodiacetate 78 as the source of anion. The reported yields of one-step syntheses were in the range of 87–99%.…”

“…For this purpose, the crude product needs to be dissolved in acetone or in a mixture of methanol and acetone or acetonitrile when working with substances that exhibit limited solubility (or insolubility) in acetone. 61 Then, the KI 39 and KCl or KBr residues and possible residues of potassium salt forms of the herbicides should be filtered off. Finally, the solvent should be evaporated, and in the final step, the product should be dried.…”

Synthesis and Characterization of Double‐Salt Herbicidal Ionic Liquids Comprising both 4‐Chloro‐2‐methylphenoxyacetate and trans‐Cinnamate Anions

“…They belong to the third generation of ILs, exhibiting specific biological activity while maintaining favorable physicochemical and chemical properties . There are reports regarding the synthesis of HILs containing synthetic auxins as an anion source (e. g. 2,4‐D, MCPA, mecoprop‐P or dicamba) . Converting known herbicides into the form of HILs increases their biological activity, improves physicochemical parameters (thermal stability, volatility, water solubility, surface activity) and reduced negative effects on the environment .…”

“…There are reports regarding the synthesis of HILs containing synthetic auxins as an anion source (e. g. 2,4‐D, MCPA, mecoprop‐P or dicamba) . Converting known herbicides into the form of HILs increases their biological activity, improves physicochemical parameters (thermal stability, volatility, water solubility, surface activity) and reduced negative effects on the environment . HILs, unlike commercial herbicides, are characterized by low volatility, which eliminates the risk of unintended contamination of other cultivated areas and minimizes the likelihood of damaging neighboring dicotyledonous crops .…”

Bifunctional Double-Salt Ionic Liquids Containing both 4-Chloro-2-Methylphenoxyacetate and l-Tryptophanate Anions with Herbicidal and Antimicrobial Activity

“…Through the use of a rationally designed cation, it is possible to obtain a compound with improved physicochemical properties that translate into herbicidal activity. 40 …”