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IONIC LIQUIDS : GREEN SOLVENTS FOR THE FUTURE

Dr.Sunita Hooda, Dr.Vandana Uberoi, Dr.Geetu Gambhir Acharya Narendra Dev College

Abstract

Ionic liquids are organic salts in which the ions are poorly coordinated, which results in these solvents being liquid below 100OC, or near room temperature (room temperature ionic liquids, RTIL’s).The cationic part of most ionic liquids are organic based moieties such as imidazolium, N-alkyl pyridinium tetra alkyl phosphonium ions. The anionic part can be organic or inorganic and include entities like halides acetate, nitrate, tetra fluoro borate hexa chloro phosphate etc.

Ionic liquids tend to be very promising solvents due to their potential to make ideal green solvents as they have negligible vapor pressure and do not evaporate into the atmosphere, making them a more environmentally responsible material than traditional volatile organic solvents. The absence of volaltility is one of the most important benefit of ionic liquids, offering a much lower toxicity as compared to low boiling solvents.They not only provide less hazardous solvent option but further the diverse selection of the cations and anions allows to engineer the physicochemical properties of RTIL’s by the choice of ionic constituents and allowing for the tailor made solvents. . For this reason, ionic liquids have been termed as “designer solvents” For example, by changing the anion or alkyl chain on 1-alkyl-3-methyl imidazoliumn cation, a wide variation in properties such as hydrophobicity, viscosity, density and salvation can be obtained.

[emim][BF4] where e: ethyl, m: methyl, im: imidazolium

Others:[emim][PF6],[emim][CF3SO3],[emim][NO3],[emim][CLO4]

In this review, ionic liquids have been studied in detail. The various examples of ionic liquids obtained from methyl imidazolium and pyridinium ions have been taken into consideration.

Ionic liquids represent a new class of salts that are distinguished by a range of useful properties such as negligible vapor pressure, thermal stability, non-flammability, high ionic conductivity ,melting point, normal workable viscosity moderate polarity and solubility of starting materials and other solvents, make them attractive as alternative medium for new synthetic pathways ,increased reaction rates and distinct selectivity in organic reactions.

The major disadvantages with ionic liquids are poor hydrolysis stability of anion, their moisture sensitivity, the difficulty of drying ionic liquids and difficulty of separation of products containing hetero atom from ionic liquid.

The ionic liquids have wide applications as clean solvents in organic synthesis, separation technology, catalyst for green chemistry,electrochemistry ,electrolytes for batteries ,photochemistry and for electro synthesis of conducting polymers. [edit] References

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