A survey of chemical catalogs uncovers over one
hundred commercially available salts
that melt below 150°C. Many others are
just above this melting point,
suggesting that many new IL might be
readily created by matching a desired cation from such a salt with a
different anion, or vice-versa. These compounds constitute incognito IL, begging to be used.
Of course, the availability of incognito IL is due to
their existing use in some other type of application. Naturally, such
pre-existing applications point to potential uses as IL for the
compounds themselves or salts related to or derived from them.
An example of a readily available, incognito IL that
creatively exploited is acetylcholine chloride. This salt, a non-toxic
natural product, melts between 147°–149 °C, making it an "ionic
liquid". Davies has recently demonstrated that it,
when combined with select inorganic salts, forms eutectics with even
lower melting points. These eutectics, themselves composed wholly of
ions, are interesting new ionic liquids with built-in, water-stable
Lewis acidic character.
Other low-melting biomolecular salts, many of them
derivatives, can be obtained commercially as well.
Examples include L-alanine ethyl
hydrochloride (mp 78 °C) and L-serine methyl
ester hydrochloride (106 °C). Like many other lower-melting
these may not be ionic liquids in a strict sense. Melts likely manifest
equilibrium concentrations of neutral species, meaning that they are
not composed only of ions. However, as melts in contact with a
secondary, low-polarity organic phase, it is doubtful that any neutral
melt component would partition into the latter, allowing the melt to
function in a fashion similar to a true ionic liquid.
At a minimum, many of the ions in these low-melting,
available salts are potentially versatile skeletons that suggest
themselves as starting points for modification into IL