A Sustainable Route towards Imidazolium Building Blocks Based on Biomass Molecules

Abstract

Imidazolium compounds are very versatile molecules that have enabled a large number of recent innovations in the field of chemistry. Among these, imidazolium-based ionic liquids (ILs) are the most prominent. Coming with beneficial solvent properties, negligible vapor pressure and high thermal stability, ILs are often classified as "green solvents". [1] A critical analysis, however, reveals that ILs synthesis and purification show a lot of room for improvement in terms of sustainability and cost reduction. This is particularly true for the so-called "task specific" ionic liquids, compounds in which the imidazolium cation has been additionally manipulated to include one or more reactive functionalities. [2] Consequently, greener methods to access ILs are still highly welcomed and are expected to expand the application range of those systems. Traditionally, heterosubstituted imidazolium scaffolds have been targeted by following the general idea that asymmetric substitution results in ILs with lower melting points. Double alkylation of imidazoles [3] has been successfully employed as a strategy for the preparation of cations decorated with hydroxyl groups, [4] thiol groups, [5] alkene groups, [6] and others. [2] Despite their popularity, quaternization reactions and the following functionalization steps are responsible for the relatively long syntheses, often characterized by high temperatures and long reaction times, accompanied by low-yielding purification procedures, [7] with the discussed implications on production costs and sustainability. Interestingly, imidazolium compounds can be easily accessed by simple modifications of the Debus-Radziszewski synthesis. [8] This convenient one-pot approach involves reaction of a primary amine, formaldehyde, and a 1,2-dicarbonyl compound, the only drawback being its limitation to the formation of homosubstituted species. Such imidazolium cations have been extensively reported, [9] but a systematic study on their properties in ILs is still missing. Besides the field of ILs, advancement in the synthesis of 1,3-homosubstituted imidazolium cations can additionally foster the development of other areas of chemistry, such as polyionic liquids (PILs), [10] N-heterocyclic carbenes, [11] antifungal drugs, [12] and carbon materials. [13] In this paper, we report a general strategy for the synthesis of symmetric, bifunctional imidazolium ionic compounds derived from readily available and sustainable starting materials, including carbohydrate fragments and simple amino acids/amines. Recently, imidazolium-based room temperature ILs with amino acids as the counterions were presented. [14] Here, we surmised that the amino group of natural amino acids could react in a Debus-Radziszewski-like reaction, thereby providing the resulting imidazolium ions with the well-known set of biological functionalities, depending on the amino acid exploited. We focused our investigation on the use of pyruvaldehyde as the 1,2-dicarbonyl scaffold instead of the commonly used glyoxal. Pyruvaldehyde has been ...

A sustainable synthesis alternative for IL-derived N-doped carbons: Bio-based-imidazolium compounds

“…Therefore, the need for reduced costs for carbon materialization of ionic liquids has been established as one of the main challenges in this field [9]. Besides existing works on protic ionic liquids [10] with regard to price and improved sustainability, we recently presented the convenient synthesis of bifunctional imidazolium compounds using natural amino acids as green starting materials [11]. The synthesis of such imidazoliums can be entirely performed according to the rules of green chemistry at reduced costs, while control over the specific N-substitution of the imidazole moiety can be achieved by selection of different amino acids.…”

Amino Acid-Derived Imidazolium Zwitterions: Building Blocks for Renewable Ionic Liquids and Materials

“…When aliphatic amines were used, ionic liquids were obtained as products, with the counterion provided by the acetic acid catalyst (13), as shown also by other groups previously (23). Unsubstituted and hydroxyl-functionalized amines could also be converted with good yields.…”

“…In a bid to synthesize imidazolium compounds from renewable resources, we developed a modified version of this long-established reaction, using amino acids as the amine component and dicarbonyl compounds which can be derived from carbohydrates. Employing acetic acid as an environmentally benign catalyst, we obtained a library of differently functionalized imidazolium compounds in a simple one-pot reaction at ambient or very moderate temperatures (13). The reaction uses reagents in stoichiometric amounts and is very atom efficient, the only side product being water (Figure 1a).…”

“…The reaction uses reagents in stoichiometric amounts and is very atom efficient, the only side product being water (Figure 1a). The different amino acid side chains conveniently add different functionalities as well as chirality to the final building block (13). All amino acid-derived imidazolium compounds formed as zwitterionic salts and were isolated as solids, which can be purified easily by removal of water (e.g.…”

Inorganic Nanomaterials Synthesis Using Ionic Liquids

“…12,17 These efforts have recently been backed up by research on the synthesis of ILs from renewable sources such as amino acids. [160][161][162] This opens up an interesting perspective for the future: nanomaterials synthesis from recycled ILs that have initially been prepared from sustainable sources.…”