3. Contents
Introduction
History
Composition
Synthesis
Physical and chemical properties
Green aspects
Toxicology
Handling
Applications
Summary
4. Introduction
New class of purely ionic, salt like materials that are liquid at unusually low
temperatures.
Official definition Ionic liquids are ionic compounds which are liquid
below100ºC.
Appreciable liquid range.
These substances are variously called liquid electrolytes, ionic melts, ionic fluids,
fused salts, liquid salts or are known as “Solvents of the future” as well as
“Designer solvents”.
5. Why ionic liquid exists in liquid state at
room temperature?
Many other salts like NaCl having small size of ions, symmetrical in shape, strongest
bond attractions, crystalline structure.
In Ionic liquids, larger size of ions and asymmetrical ions, weak bond attraction, liquid
in state at room temperature.
6. The driving forces
The problems in the chemical industry with the volatile organic compounds
(VOCs) :
• toxic and/or hazardous
• serious environmental issues, such as atmospheric emissions and
contamination of aqueous effluents.
The driving force in the quest for novel reaction media:
• greener processes
• recycling homogeneous catalysts
7. History
The description of a low melting point salt Ethyl ammonium nitrate( M.P:12ºC) in
1914 by Walden.
The first room temperature ionic liquid N-ethylpyridinium bromide-aluminium
chloride in 1951.
The most stable and conductive salt is 1,3-dialkylimidazolium salts in 1982.
The hydrophobic ionic liquid is 1-ethyl-3-methylimidazolium tetraflouroborate in
1992.
8.
9. Composition
There are a number of different cations and anions combinations that may
result in salts having low melting point.
To make an ionic liquid, researchers can select from dozens of small
anions, such as hexafluorophosphate ([PF6]–) and tetrafluoroborate ([BF4]–),
and hundreds of thousands of large cations, such as 1-hexyl-3-
methylimidazolium or 1-butyl-3-methylimidazolium. Ionic liquids are thus
"designer solvents".
Chemists are free to pick and choose among the ions to make a liquid that
suits a particular need, such as dissolving certain chemicals in a reaction or
extracting specific molecules from a solution.
14. Properties
Easy separation.
Very low vapor pressure.
Non flammable substance.
High thermally stable.
High mechanically stable.
Electrochemically stable
Low toxicity.
Non volatile.
15. Advantages of ionic liquids over
organic solvents
High ionic conductivity.
Non Flammable.
Non Volatile.
High thermal stability.
Wide temperature range for liquid phase(-40 to +200 degree Celsius).
Highly solvating yet non coordinating.
Good solvents for many organic and non organic materials.
16. Why consider ionic liquids as GREEN
SOLVENTS
Low melting salts(-60º)
Very low vapor pressure(good).
Non flammable(good).
Wide liquid range(300ºC)(good).
Moderate to high viscosity(bad).
Solvent properties can be controlled by selection of anion and cation-
hence often termed designer solvents(good)
BUT-some ionic liquids are toxic to the environment and humans.
17. Toxicology
The green character of ionic liquids has been justified with their negligible
vapor pressure, but if ionic liquids are water soluble, enter environment
(accidental spills, effluents).
Halogen containing anions with poor stability in water ,toxic species such
as HCL or HF might be liberated.
Ionic liquids with functionalised side chains allow enzymatic hydrolysis.
Many longer alkyl chain length of imidazolium ILs resulted in a stronger
inhibition of enzyme.
18. Handling of ionic liquids
New liquids are free from many of the hydrolysis problems that make the
halogenoaluminates(III) so difficult to handle.
Most ammonium and imidazolium salts are hygroscopic and if used in
open vessels, hydration will almost certainly occur.
Room-temperature ionic liquids [EtNH3][NO3], [emim][NO3], and
[emim][ClO4]. Organic nitrates and perchlorates are potentially explosive,
especially when rigorously dried. Although no problems have been
reported, care should be used at all times when handling them.
Nowadays the most widely used ionic liquids are probably N,N-
dialkylimidazolium salts
19.
20.
21. Concluding remarks
Future ionic liquids research needs
Toxicological information.
Develeping new ionic liquids.
Database with all properties.
Methods of synthesis less expensive.
Easier availability.
22. References
Further information regarding physical properties, chemistry, and uses of
ionic liquids:
[1] Welton T. Chem . Rev., 1999, 99: 2071.
[2] Wasserscheid P, Keim W. Angew Chem. .Int. Ed. Engl., 2000, 39: 3722.
[3] Freemantle M. (a) Chem . Eng . News, 2000, 78 (May)15: 37-39; (b) Chem .
Eng . News, 2001, 79 (Jan)1: 21-25.
[4] Earle M J, Seddon K R. Pure Appl, Chem., 2000, 72 (7): 1391-1398.
[5] Chum H L, Koch V N et al. J. Am. Chem, Soc., 1975, 97: 3264 .
[6] Wilkes JS et al . Inorg . Chem., 1982, 21: 1236.
[7] a) Blanchard L A et al. Nature, 1999, 399: 28; b) Blanchard L A et al. Ind. Egn.
Chem. Res., 2001, 40: 287.
[8] Chauvin Y, Mubmann L, Olivier H. Angew. Chem. Int. Engl., 1995, 34: 269.
