Abstract

A series of solvent-stabilized ionic liquid fluorides were prepared, [EMIM]F.nCH3COOH n = 1. 0, 1.6, 2.1, 2.4, and 3.2, either via exchange from the chloride salt using KF or AgF, or by neutralization of the hydroxide salt using HF. Azeotrope drying was used to remove water. Their viscosity, conductivity and density properties were determined. A diethanol solvate of the triaminocyclopropenium salt [C3(NPr2)3]F was found to be stable and its viscosity, conductivity and density properties were also determined. The monoethanol solvate, however, was found to be unstable with trace water present. Intramolecular stabilization of fluoride was achieved by using OH functionalized cations: [C3(NEt2)2N(CH2CH2OH)2]F, [C3(N(CH2CH2OH)2)3]F, and [Me3NCH2CH2OH]F.H2O, The first of these is an ionic liquid at ambient temperature and has a TGA mass loss onset at 175°C, indicating a useful range of liquid state stability.

Highlights

  • Research in Ionic Liquids (ILs) has explored a vast variety of anion types, revealing a wide range of properties and applications

  • We report on TAC fluoride salts with interand intra-molecular alcohol solvate interactions

  • Three classes of cations were studied for the preparation of fluoride ionic liquids: the tris(dialkylamino)cyclopropenium cation [C3(NPr2)3]+, the imidazolium cation [EMIM]+, and hydroxyl-functionalized salts

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Summary

INTRODUCTION

Research in Ionic Liquids (ILs) has explored a vast variety of anion types, revealing a wide range of properties and applications. Fluoride anions have the potential to make ionic liquids with interesting properties due to the reactivity of fluoride (Maiti et al, 2008; Mallik and Siepmann, 2010) Fluoride salts, such as tetrabutylammonium fluoride (TBAF), have many uses as fluorinating reagents and for the removal of silicon-based protecting groups. TAC cations are sensitive to strong nucleophiles, such as hydroxide, and possibly fluoride itself For this reason, even if triaminocyclopropenium salts proved to be stable to fluoride, any kind of naked fluoride ionic liquid would be highly moisture sensitive. Prompted by earlier work on dimeric and higher order oligomeric acetic acid anions (Johansson et al, 2008), acetic acid was investigated as a solvate molecule with imidazolium fluoride salts Both the [AcOHF]− and [(AcOH)2F]− species, shown below, have been observed previously by NMR at sub-ambient temperature (Golubev et al, 2004)

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