Fatty acid based ionic liquids from methyl carbonates: synthesis and characterization.

In the last fifteen years, ionic liquids (ILs) have attracted considerable attention. Through continuous efforts of numerous researchers, ILs have achieved not only a consolidated popularity as “green” solvents for synthesis and extraction processes, but also as powerful catalysts, electrolytes, precursors or additives to employ in several of areas. The most attractive feature of these salts, liquid at or near room temperature, is the possibility to modify the principal physico-chemical and biological properties varying cation and/or anion structure. Herein, we report a halogen free procedure to prepare fluorine-free hydrophobic ILs. ILs composed by an imidazolium or ammonium cation and a fatty acid anion, with different chain length and saturation degree, have been synthesized by simple addition of a fatty acid to methylcarbonate based ILs in methanol. The acidity of the fatty acid is indeed sufficient to decompose the methylcarbonate anion to methanol and carbon dioxide. With respect to the classical procedure to prepare carboxylic ILs, this synthetic pathway starts from methycarbonates, prepared by alkylation of the proper base with the “green” dimethylcarbonate, and avoids metathesis reactions through silver salts. Critical points characterizing this apparently simple synthetic procedure will be evidenced. The principal physico-chemical properties of this class of highly hydrophobic ILs [1], characterized by good thermal and chemical stability, as well as the possible applications as diathermic fluids or organized media will be discussed.