Twenty eight new dicamba (3,6-dichloro-2-methoxybenzoic acid)-based herbicidal salts, have been synthesized and characterized in order to attempt to improve the efficacy of this widely known herbicide used to protect maize, grassland, and other cultures. The new compounds, most of which are ionic liquids by definition and three of which are solids melting above 100 °C, were prepared by pairing quaternary tetraalkyl- or alkoxyammonium, piperidinium, imidazolium, pyridinium, morpholinium, quinolinium, and phosphonium cations with the dicamba anion. Growth chamber and field test data suggested that ionic liquid forms of dicamba offer substantially increased efficacy which would allow less to be applied in the field. Compared to the commercial dicamba free acid product, improved physical properties were observed including higher decomposition temperatures and reduced volatilities, suggesting a potential reduction of overall environmental impact of this herbicide.

The transformation of agrochemicals into herbicidal ionic liquids (HILs) has been suggested as a solution to problems associated with commercial forms of herbicides. The aim of this review was to summarise the latest progress in the field of HILs, including their synthesis as well as physicochemical and biological properties, and to address the areas which require further research in order to ensure their safe commercialization (e.g. data regarding biodegradability, toxicity and environmental fate). The first part of the review provides an in-depth summary of current state of knowledge regarding HILs, particularly the anions and cations used for their synthesis. The second part highlight the employed synthesis methods and elucidates their respective advantages and limitations. The third section is focused on the characterization of HILs with emphasis on the methods and factors which are significant in terms of their practical application. Subsequently, the issues associated with the biodegradation and toxic effects of HILs were discussed based on the relevant literature reports. All sections include comprehensively tabularised data in order to enable rapid comparison of utilized approaches. Finally, all the findings were critically analysed in terms of crucial disadvantages (especially the lack of standardization), which allowed to establish future recommendations and basic guidelines that were presented in the last section.

Three herbicidal ionic liquids (HILs)—alkyldi(2-hydroxyethyl)methylammonium (2,4-dichlorophenoxy)acetate, dialkyldimethylammonium (2,4-dichlorophenoxy)acetate, and alkyltrimethylammonium (2,4-dichlorophenoxy)acetate—were synthesized and their activity against broad-leaved weeds was investigated under field conditions. HILs as [cation][2,4-D] used in winter wheat were much more active compared to 2,4-D-dimethylammonium salt and demonstrated efficacy similar to 2,4-D 2-ethylhexyl ester. HILs exhibited desirable surface properties such as low contact angle of droplets and low surface tension. Moreover, the HILs may be safer to operators and neighboring plants due to their nonvolatile nature. HILs at 450 g ha⁻¹of 2,4-D did not injure wheat.