Design of Novel Solvents for Agrochemical Formulations via Solvatochromic Methods using N-Alkyl substituted Amides as Example

Abstract

Finding new candidate solvents that can work as replacers for banned solvents, or that could be an improvement to existing solvents, is a time-consuming procedure. It is important to know how solvent structure affects interactions with active ingredients and how it will affect the performance in the application. To fully understand the interactions between solvents and solutes, there is a need to understand the types of interactions that are involved in such systems. This article discusses polar interaction between solvents and solutes and presents the methods that monitor polarity. Improved methods to monitor solute solubility and water solubility are also presented. Two classes of solvents are used as examples, namely, N,N-dimethyl alkaneamides and N-alkyl, N-methyl formamides. Tebuconazole is used as a model solute. The solubility of tebuconazole in the mentioned solvents as well as formulation stability is related to fundamental interaction parameters. It is clear from the analysis that there exists a correlation between the β-parameter (electron donating properties) and the solubility of tebuconazole for amide solvents. It can also be seen that the two classes of solvents investigated in this study interact to a different extent with water (i.e. both the solubility of solvent in water and the solubility of water in the solvent). From the results, it is also clear that the N-decyl, N-methyl formamide is the best suited solvent to obtain stable formulations and emulsions at low temperature for high concentrations of tebuconazole.