Vapor Pressure of Ionic Liquids with a Common Tetrabutylammonium Cation and Three Different Anions

Abstract

The vapor pressures, pv, of three ionic compounds used as starting materials of deep eutectic systems, namely, tetrabutylammonium bromide (TBA-Br), tetrabutylammonium trifluoromethanesulfonate (TBA-TFO), and tetrabutylammonium bis(trifluoromethanesulfonyl)imide (TBA-NTF2), were measured using isothermal thermogravimetry. TBA-Br displays large values of pv, reaching ≈700 Pa at 170 °C. TBA-NTF2 is the less volatile liquid, with a vapor pressure of ≈1 Pa at 240 °C, while TBA-TFO has a slightly higher value of pv, of about 3 Pa at the same temperature. The values of pv for the NTF2-containing ionic compound are comparable to those of ionic liquids containing the same anion. The obtained mean vaporization enthalpy, ΔHvap, for TBA-Br and TBA-TFO (≈170 kJ mol−1) is higher than for TBA-NTF2 (≈145 kJ mol−1). The obtained vaporization enthalpy values fall within the typical range observed for ionic liquids.

Keywords

• ionic liquids
• vapor pressure
• thermal analysis
• tetrabutylammonium
• bromide
• trifluoromethanesulfonate