Protic Ionic Liquids with Chelating Amine

Abstract

In this review, we aim to present the unique physicochemical properties of protic ionic liquids (PILs) composed of alkyl (= hexyl, octyl, and 2-ethylhexyl) ethylenediaminium cations paired with trifluoroacetate (= TFA), trifluoromethanesulfonate (= TFS), bis(trifluoromethylsulfonyl)imide (= TFSA) anions, and acyl (= butanoyl, hexanoyl, octanoyl, decanoyl, and dodecanoyl) alaninate anions. Our primary objective is to evaluate the performance of these PILs, particularly those with hexyl- or 2-ethylhexylethylenediaminium cations, which demonstrate the potential for forming room-temperature PILs with lower viscosity and higher electroconductivity. Furthermore, we investigate the thermal degradation temperatures, revealing that PILs with TFSA anions possess the highest thermal stability, followed by TFS, acylalaninate, and TFA anions. The distinctive chelating ethylenediamine moiety in the cationic unit of these PILs, especially in AA-PILs with acylalaninate anions, enhances their ability to encapsulate transition metal ions, making them highly effective for metal ion coordination, with a preference order of Cu²⁺ > Co²⁺ > Ni²⁺. This study underscores the potential of these PILs for applications in metal-containing wastewater treatment and the synthesis of metal nanomaterials, highlighting their versatility and importance in these fields.