NMR Characterization of Ionicity and Transport Properties for a Series of Diethylmethylamine Based Protic Ionic Liquids

Abstract

The ionicity and transport properties of a series of diethylmethylamine (DEMA) based protic ionic liquids (PILs) were characterized, principally utilizing nuclear magnetic resonance (NMR) spectroscopy. PILs were formed via the protonation of DEMA by an array of acids spanning a large range of acidities. A correlation between the (1)H chemical shift of the exchangeable proton and the acidity of the acid used for the synthesis of the PIL was observed. The gas phase proton affinity of the acid was found to be a better predictor of the extent of proton transfer than the commonly used aqueous ΔpKa. Pulsed field gradient (PFG) NMR was used to determine the diffusivity of the exchangeable proton in a subset of the PILs. The exchangeable proton diffuses with the acid if the PIL is synthesized with a weak acid, and with the base if a strong acid is used. The ionicity of the PILs was characterized using the Walden analysis and by comparing to the ideal Nernst-Einstein conductivity predicted from the (1)H PFG-NMR results.

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity

“…For confirmation of this remarkable result,w ea lso made as eparatee xperimental study utilizing the alternative singlecation-probe approach that has been developed here [74,75] and elsewhere [14] based on the chemical shift of protons transferred to as elected, and stronger,B r ønsted base, for instance, diethyl methyl amine, DEMA, as featured in ac ompanion study. [75] In Ta ble 3w el ist additional NÀHc hemical shifts in the liquid states of PILs that we have obtained with the anionsA lCl 4 À , SbF 6 À ,A sF 6 À BF 4 À and HSO 4 À ,t he last four of which also establish the superacid order in Figure 6.…”

Transport properties of protic and aprotic guanidinium ionic liquids

“…12,24 Watanabe et al also found similar trends but lower ionicity values for ILs from the larger superbase DBU. 12 The observed reciprocal Haven ratios of the protic TMG ILs are also considerably higher than those of other PILs such as ammonium 70,71 or amidinium 12 underlining its correlation with the highly basic nature of the precursor. 12 To the best of our knowledge these are also the highest I HR values reported for PILs so far.…”

“…those of phosphonium ILs from 0.47 to 0.71 (ref. 27) and those of ammonium from 0.06 to 0.62 71. Values reported for AILs consisting of aromatic cations with…”

A Simple Approach to Achieve Self‐Buffering Protic Ionic Liquid‐Water Mixtures

“…Firstly, whether the stoichiometries of acid and base affect the proton transfer (or proton activity, which is represented by N−H chemical shift from NMR since the shift of this exchangeable proton has information about how strongly the proton is associated with the base) of pILs and pH of pIL‐water mixtures were evaluated. This N−H chemical shift is a good indicator of proton transfer which has been studied over years . TeaMs was selected as it has previously been used in bio‐applications …”