In the footsteps of August Michaelis: Syntheses and Thermodynamics of Extremely Low‐Volatile Ionic Liquids

Abstract

A series of nine different known ionic liquids or low melting salts was synthesised and purified. They are composed of the [NTf2]– (bis(trifluoromethane)sulfonimide), [OTf]– (trifluoro‐methane‐sulfonate), or [B(CN)4]– (tetracyanidoborate) anion and [Ph4P]+ (tetraphenylphosphonium), [Ph3BzP]+ (triphenylbenzyl phosphonium), [nBu4P]+ (tetra‐nbutylphosphonium), [nBuPh3P]+ (tri‐phenyl‐nbutylphosphonium), [nBu4N]+ (tetra‐nbutylammonium), or the [PPN]+ (bis(triphenylphosphine)iminium) cation. Precise vapour pressure data and enthalpies of vaporisation were measured using the Quartz Crystal Microbalance (QCM) method and evaluated. Structure‐property relations are established using the obtained data as well as literature known data of ILs with alkyl‐substituted imidazolium cations. It turns out that ILs with the tetracyanidoborate anion have even higher values of the enthalpy of vaporisation than those with the common [NTf2]− or [OTf]− anion and therefore are even less volatile.

Thermal Decomposition, Low Temperature Phase Transitions and Vapor Pressure of Less Common Ionic Liquids Based on the Bis(trifuoromethanesulfonyl)imide Anion

“…For the presently investigated ionic liquids, it varies from 136 ± 18 kJ/mol for m-C 6 H 4 (CH 2 ImMe)][NTf 2 ] 2 to 147 ± 12 and 147 ± 13 kJ/mol for [DABCO10][NTf 2 ] and [p-C 6 H 4 (CH 2 ImBu)][NTf 2 ] 2 , respectively, and finally to 180 ± 17 kJ/mol for [C 6 Py][NTf 2 ]. These values are consistent with those previously reported for the other ionic liquids [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

“…ILs containing the diethyl phosphate [ 25 ], thiocyanate [ 26 ], methanesulfonate [ 27 ], formate and acetate [ 28 ] anions displayed high values of the vapor pressure, while those based on the iodide, bromide or chlorine anions have extremely low values of p v [ 29 , 30 ]. ILs containing the B(CN) 4 anion have p v comparable to that of NTf 2 samples [ 31 ]. Bulow et al reported a comparison of the vapor pressure of ILs containing the same 1-ethyl-3-methyl-imidazolium cation and a series of anions, such as PF 6 , B(CN) 4 , (C 2 H 5 O) 2 PO 2 , NTf 2 , SCN, CF 3 CO 2 , CF 3 SO 3 , BF 4 , C(CN) 3 , (C 2 F 5 ) 3 PF 3 , 4-CH 3 -Ph-SO 3 [ 32 ].…”