Hello! I am wondering how one is supposed to use ionic liquids. For example 1-butyl-3-methylimidazolium bromide is initially in the solid state. But every publication I have found when analyzing stoichiometry calculates it by volume. Is there a special work up or preparation before the use in a reaction?
Hello, You can weight this ionic salt according to stoichiometry needed. Actually above 70 degree celsius , it act as ionic liquid otherwiswe it is a salt.
Here i am attaching one link, see this paper. These people have taken weight according to their need.
http://www.sciencedirect.com/science/article/pii/S1026309811000708
Thank you Anuj! Actually I did use it this way but I since it was my first time using one I wanted to be on the safe side and ask about it someone who has more experience. And if I may ask another question.. How are we supposed to re-use the ionic liquid? The reaction I am pursuing is a dehydration reaction. And as you said this is a salt so after the reaction there water in the mix. Standard drying procedures would be enough?
Hello Maria, if possible do workup using water since it is a salt, it will dissolve easily in water. Otherwise check the solubility of ionic salt in polar solvent in which your compound is not soluble.I more thing, freeze your reaction mixture, ionic salt will become solid, then seperate it from your product using different solvent.
I think 1-butyl-3-methylimidazolium bromide comes under class of room temperature ionic liquids (RTILs). Generally RTILs exist in liquid form in pure state. In addition also ensure the absence of water content in the IL.The IL can be purified by following ways
a) Stir the IL with ethyl acetate settle decant, repeat twice. ( As the IL is insoluble in Ethyl acetate).
b) For water removal add E.A heat to 70 °C maintain 30 min, cool the rxn mass deacnt , remove the traces of E.A roto vap.
Good morning, the definition of ionic liquid is a salt that melts below 100°C. As such, BMIM Br is an IL, but since it has a melting point around 80°C, it is not a RTIL. Most ILs, even if liquid at RT are undercooled melts, i.e. you can have BMIM Br liquid at RT if you melt it and cool it very slowly without touching it. But the moment you shake it, or try to triturate, it will crystallize pretty fast and give you a pretty hard block of solid salt. This of course applies for pure BMIM Br, if you have a few percent of water in it, it will stay liquid.
Let me disclose! In most cases the synthetic ionic liquids have negligible impurities. These impurities inhibited formation of crystalline structure and forms viscous oil which are not solidify even at refrigerator. The impurities are water, reminding starting materials, and some by-product from side reactions.... For analytical experiment it is better to buy ionic liquids from chemical suppliers and do not use self-synthetic ionic liquids.
Sincerely
You all have been very helpful! Regarding the matter that if BMIM is a RTIL indeed it isn't. I was wondering about it because of the habit to report the quantity used in volume insted of mass. As for the re-using since the reaction I used it for is a dehydration I am afraid I cannot avoid the presence of water. However in many papers people claim that one of the advantages of ionic liquids is that you can re-use them and I was thinking if there is an appropriate purification technique. For sure one cannnot use it as it is after being used. Thanks again for the kind replies.
Dear Maria,
The definition of RTIL is: the IL which its melting point is below 100 dC.
The ILs can simply purified by simple vacuum distillation.
I would just wash it with ethylacetate in order to remove any organic impurities that might have been introduced during the reaction 8as long as they are soluble in it of course) and then dry it under high vacuum for a few days.
since most ionic liquids are liquids at room temperature e.g 1-butyl-3-methylimidazolium bromide you can separate this doing a liquid-liquid portioning with ethyl acetate.
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