Non conventional anions2



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.

Examples:


  • Acetylcholine chloride
  • An example of a readily available, incognito IL that has already been 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.

  • Amino acid derivatives
  • Other low-melting biomolecular salts, many of them amino acid derivatives, can be obtained commercially as well.
    Examples include L-alanine ethyl ester hydrochloride (mp 78 °C) and L-serine methyl ester hydrochloride (106 °C). Like many other lower-melting salts, 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, commercially available salts are potentially versatile skeletons that suggest themselves as starting points for modification into IL with built-in functional groups.

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