alkylammonium halides are commercially
available or they can be
prepared simply by the reaction of the appropriate halogenoalkane and
amine. Preparation of the pyridinium and imidazolium halides can be
volatile halogenoalkanes, the low boiling
points lead to preparations requiring either a sealed tube, such as in
the synthesis of [emim]Cl (where [emim]+ is the
1-ethyl-3-methylimidazolium cation), or an elaborate reaction still.
Hence, the use of salts with longer chain substituents,
[bmim]Cl (where [bmim]+ is the 1-butyl-3-methylimidazolium
that can be prepared in conventional glassware by heating under reflux
has become popular.
1992 the first of the new ionic liquids,
via metathesis of [emim]I with Ag[BF4] in methanol. This
salt also has
a melting point of 12 °C and may be prepared considerably more
cheaply using [NH4][BF4] in acetone.
with its relative moisture stability and
its immiscibility with a
number of organic solvents is leading to its increasing use in biphasic
The preparation of [emim][PF6]
this time it was prepared by reaction of [emim]Cl with HPF6.
has a melting point of 60 °C, which makes it slightly less
attractive than the [BF4]-
salt, if room
desired. Since then, thiocyanate, nonafluorobutanesulfonate,
tris((trifluoromethyl)sulfonyl)methide, trifluoroacetate, and
heptafluorobutanoate salts have all been prepared by metathesis
reactions are good candidates for
those preparing new ionic liquids for the first time. However, they can
leave the ionic liquids contaminated with a small amount of halide ions
that may react with solute materials.