Preparation of 1-butyl-3-methylimidazolium derivative


To synthesize in water 1-butyl-3-methylimidazolium derivative, which has the property of being a ionic liquid.

synthesis of 1-butyl-3-methylimidazolium derivative
Synthesis of 1-butyl-3-methylimidazolium derivative


The so-called ionic liquids are salts in which at least one of their components is an organic compound that has a delocalized charge. This characteristic prevents the formation of stable crystal lattices because both the cation and the anion are poorly coordinated. Most of these salts, called r.t. ionic liquids (RTILs), are liquids below 100 ºC, or even at r.t. The nature and the properties of ionic liquids are diverse, so they can be used as solvents, separation media, electrolytes, or lubricants, and, depending on their structure, they can be miscible with water or organic solvents. In addition, some transition metal catalysts are soluble in ionic liquids, and both may be recycled after extraction with water. The potential of these new solvents is enormous in many chemical processes, in work- up procedures, and in many cases, they are considered green solvents because of their origin (it is possible to prepare from renewable sources) and their properties (non-volatile compounds, reusable many times, and biodegradable). The only limitation for their massive use in many conventional organic reactions at a large scale is their high price.
In this experiment, the synthesis of an ionic liquid is described starting from 1-methylimidazole, 1-bromobutane, and potassium hexafluorophosphate (KPF6) in an organic solvent-free reaction.

Experimental procedure

In a 25 ml round-bottom flask magnetically stirred on a hot plate, place water (1 ml), 1-methylimidazole (1 ml), and 1-bromobutane (1.35 ml) (use separately marked pipettes to measure each reagent). Adjust a condenser on the flask and reflux the reaction mixture for 1.5 h. By that time, a homogeneous solution will result (no oily appearance). Allow the reaction mixture to cool to r.t., and add distilled water (10 ml) followed by KPF6 (2.3 g). If necessary, gently break the chunks of KPF6, if any, with a glass rod or a spatula, and swirl the resulting mixture for 10-15 min. Two clear phases should appear. Transfer the whole mixture into a 125 ml separatory funnel, wash the 25 ml round-bottom flask with CH2Cl2 (25 ml), and add it to the separatory funnel. Perform the liquid-liquid extraction.

DANGER! “Do not forget to vent!”


Drain the CH2Cl2 layer into a 100 ml Erlenmeyer flask, and wash to extract the aqueous layer (upper) with another portion of fresh CH2Cl2 (10 ml). Combine the organic layers of CH2Cl2, and dry them with anhydrous Na2SO4; 1-2 scoops should be enough. Eliminate the desiccant by gravity filtration, and pour the filtrate into a dry 25 ml and tared round-bottom flask. Eliminate the solvent under vacuum (rotary evaporator) and weigh the flask again to calculate the yield (estimated 76 %).


Physico-chemical properties

This table collects data for the molecular weight (Mw), melting point (M.p.) boiling point (B.p.) and density of the reactives and compounds used in this laboratory experiment.

Name Mw (g/mol) M.p. (ºC) B.p. (ºC) Density (g/ml)
Na2SO4142.04884 -2.630

GHS pictograms

Hazard pictograms form part of the international Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and are collected in the followinf Table for the chemical compounds used in this experiment.

Name GHS
1-Methylimidazole ghs06  Danger Toxic cat. 1–3 pictogram ghs05  Danger Warning Corrosive cat. 1 pictogram
1-Bromobutane ghs02  Danger Warning Flammable pictogram ghs07  Warning Toxic cat. 4 Irritant cat. 2 or 3 Lower systemic health hazards pictogram ghs09  Warning (for cat. 1) (for cat. 2 no signal word) Environmental hazard pictogram
CH2Cl2 ghs08  Danger Warning Systemic health hazards pictogram
Na2SO4 Non-hazardous

International Chemical Identifier

The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.