Efficient, halide free synthesis of new, low cost ionic liquids: 1,3-dialkylimidazolium salts containing methyl- and ethyl-sulfate anions

Abstract

New low-cost ionic liquids containing methyl-and ethyl-sulfate anions can be easily and efficiently prepared under ambient conditions by the reaction of 1-alkylimidazoles with dimethyl sulfate and diethyl sulfate. The preparation and characterization of a series of 1,3-dialkylimidazolium alkyl sulfate and 1,2,3-trialkylimidazolium alkyl sulfate salts are reported. 1,3-Dialkylimidazolium salts containing at least one non-methyl N-alkyl substituent are liquids at, or below room, temperature. Three salts were crystalline at room temperature, the single crystal X-ray structure of 1,3-dimethylimidazolium methyl sulfate was determined and shows the formation of discrete ribbons comprising of two anion-cation hydrogen-bonded chains linked via intra-chain hydrogen-bonding, but little, or no inter-ribbon hydrogen-bonding. The salts are stable, water soluble, inherently 'chloride-free', display an electrochemical window of greater than 4 V, and can be used as alternatives to the corresponding halide salts in metathesis reactions to prepare other ionic liquids including 1-butyl-3-methylimidazolium hexafluorophosphate.

Ionic Liquids Made with Dimethyl Carbonate: Solvents as well as Boosted Basic Catalysts for the Michael Reaction

“…OCOO] (14): Compound 14 (20.8 g, 98 %) was synthesised using the same procedure as for [TOMA]A C H T U N G T R E N N U N G [CH 3 General procedure for the Michael reactions: A 7 mL glass reactor equipped with a side screw-capped neck for the withdrawal of samples and a condenser was charged with the reagents and the chosen catalyst (see Tables 2 and 3 and Figure 2). The reactor was heated to the desired temperature (4-40 8C) and the mixture was kept under magnetic stirring throughout the reaction.…”

“…[3,10] In addition, the materials thus prepared inevitably contain residual undesirable halide ions. Although these steps can be optimised in a number of ways, for example, by halide-free syntheses, [11][12][13] they still often use hazardous and highly toxic reagents such as methyl halides and dimethylsulfate (DMS), [14] and generate unwanted byproducts. Quaternarisation of nitrogen (or phosphorous) generates the ionic onium (Q + ) species, and depending on the methylating agent used, this step ends up incorporating the counteranion in the IL.…”

Phosphonium nitrate ionic liquid catalysed electrophilic aromatic oxychlorination

“…16 2 The ionic liquids that are obtained are intrinsically halide free, generally an advantage since residual halides are an undesirable impurity.…”

Use of ionic liquids in biodiesel production: a review

“…This excess is then evaporated and 1-n-butyl-3-methylimidazolium chloride (or bromide) is obtained (Wilkes et al, 1982). The resulting organic salt can be used in three different ways: directly as an ionic liquid; it can be mixed with aluminum chloride or other halometallates, forming chlorometallate-based ionic liquids, widely studied in the literature; or for subsequent metathesis (Holbrey et al, 2002). The metathesis reaction is simply an exchange between cations and anions of the compounds involved.…”

“…Choline chloride costs about US$ 25 (250 grams), but can be bought in 5 kilos bottles for US$ 273 from traditional suppliers. Holbrey et al (2002) prepared an easy and efficient low cost ionic liquid containing methyl and ethyl sulfate anions through the reaction of 1-methylimidazolium (US$ 65 per 250 g) with dimethyl sulfate (US$ 20 per 250 mL) and diethylsulfate (US$ 30 per 250 mL), all prices obtained on the Sigma-Aldrich website.…”