Tuning the Solubility of the Herbicide Bentazon: From Salt to Neutral and to Inclusion Complexes

We report on the mechanochemical synthesis of inclusion complexes obtained by reacting the neutral crystalline herbicide bentazon (HBtz) with native cyclodextrins (CDs). The reaction of HBtz with γ-CD resulted in the formation of the inclusion complexes [β-CD·HBtz]·6H2O and [γ-CD·HBtz]·8H2O, which were characterized via a combination of X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and calorimetric measurements. No complexation, on the contrary, was achieved upon the reaction of HBtz with α-CD. The salt NaBtz·1.75H2O, widely used as a water-soluble salt of bentazon for the manufacturing of agrochemicals, was also synthesized and structurally characterized, and its solubility and dissolution properties were compared to those of neutral HBtz and of the β-CD and γ-CD inclusion complexes. It was found that the behavior of [β-CD·HBtz]·6H2O and [γ-CD·HBtz]·8H2O in water is similar, with dissolution rates of 28.4 ng·L-1·min-1and 39.8 ng·L-1·min-1, respectively, and is intermediate between those of NaBtz·1.75H2O (228 ng·L-1·min-1) and neutral bentazon (3.5 ng·L-1·min-1). These results were also compared with those of the dehydrated inclusion complexes, which displayed intermediate dissolution rates between hydrous complexes and NaBtz·1.75H2O. All findings indicate that the inclusion of HBtz in β-CD and γ-CD might represent a viable alternative for the preparation of environmentally friendly agrochemicals with controlled bentazon release to be used in the formulation of herbicides.