This
study presents the properties of a new group of ionic liquids
(ILs) based on various cations and pelargonic acid, a natural nonselective
herbicide. The obtained bio-ILs were obtained with high yield (>92%)
using a metathesis reaction or neutralization of quaternary ammonium
hydroxides and characterized in terms of physicochemical properties.
Tests under greenhouse conditions confirmed the superior herbicidal
activity of ILs compared to pure pelargonic acid, especially against
white mustard (5–10-fold higher efficacy of ILs). Further studies
under field conditions revealed that tetrabutylammonium, benzalkonium,
and oleyltrimethylammonium pelargonates exhibited the highest efficiency
(50.5%, 49.5%, and 46.7%, respectively) at an approximately 3-fold
lower dose of pelargonic acid (2.72 kg per 1 ha) compared to that
used in commercial products (8–11 kg per 1 ha). This allows
classification of the synthesized ILs as bioherbicidal ionic liquids
(bio-HILs). In addition to bio-HILs, two new auxins were also obtained.
Evaluation of antimicrobial activity indicated that the most potent
effect was observed in the case of salts with oleyltrimethylammonium
and tallowtrimethylammonium cations [minimum inhibitory concentration
(MIC), minimum bactericidal concentration (MBC), and minimum fungicidal
concentration (MFC) values lower by 2 orders of magnitude compared
to pelargonic acid]. The fundamental influence of the cation was also
observed during biodegradability assay, as the results varied from
0% to 85% (the highest biodegradability was observed in the case of
dodecylbetainium and tetrabutylammonium pelargonates). The computational
data suggested that biodegradation efficiency seems to be influenced
by the interactions between the cation and the anion. The performed
toxicity tests allowed classification of the obtained bio-HILs as
category V [di(hydrogenated tallow)dimethylammonium pelargonate] or
category IV compounds against rats.
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