Physicochemical study of diethylmethylammonium methanesulfonate under anhydrous conditions

Abstract

The protic ionic liquid diethylmethylammonium methanesulfonate ([DEMA][OMs]) was analyzed in depth by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, 2 Raman spectroscopy and broadband dielectric spectroscopy (BDS) under anhydrous conditions. Karl Fischer titration, NMR and FT-IR spectra confirmed the high purity of [DEMA][OMs]. The melting point (37.7 °C) and the freezing point (14.0 °C) obtained by DSC agree well with the values determined by BDS (40.0 °C and 14.0 °C). The dc conductivity (σdc) above the melting/freezing point obeys Vogel-Fulcher-Tammann (VFT) equation well and thus the proton conduction in [DEMA][OMs] is assumed to be dominated by the vehicle mechanism. In contrast, the σdc below the melting/freezing point can be fitted by the Arrhenius equation separately and therefore the proton conduction is most likely governed by the proton-hopping mechanism. The non-negligible influence of previously reported low water contents on the physicochemical properties of [DEMA][OMs] is found, indicating the importance of reducing water content as much as possible for the study of "intrinsic" properties of protic ionic liquids.

New Experimental Data on Thermodynamic Properties of the Aqueous Solution of N,N-Diethyl-N-methylammonium Bromide and N,N-Diethyl-N-methylammonium Methanesulfonate

“…It was shown that the obtained melting point ( T m = 283.6 K with Δ m H = 9.78 kJ·mol –1 ) is in good agreement with the literature value reported by Nakamoto and Watanabe . The melting point is significantly lower than the value reported by Pan et al (310.85 K) . It is worth adding that the water content in the methanesulfonate-based IL tested in this work is high as presented in Table .…”

“…Because Nakamoto and Watanabe do not show water content in [N H,1,2,2 ]­[CH 3 SO 3 ], there is no certainty whether the declared melting point applies to a pure compound. In addition, the melting point published by Pan et al for this IL is definitely higher, which results from a lower water content. Despite this, this temperature is also difficult to consider as the temperature of a pure IL as the authors declare a water content of 7000 ppm.…”

“…19 The melting point is significantly lower than the value reported by Pan et al (310.85 K). 20 It is worth adding that the water content in the methanesulfonate-based IL tested in this work is high as presented in Table 2. Therefore, the melting temperature reported in Table 3 is actually the melting point of the (IL + water, x 1 = 0.7782) system.…”

Phase-dependent dielectric properties and proton conduction of neopentyl glycol

“…To study σ dc in terms of energy landscape for the related temperature range, the activation energies in phase I and the melt phase are calculated based on eqn (6) , which can be obtained by performing partial differentiation of eqn (3) in its logarithmic form with respect to T ( eqn (5) ). 41,46,47 E a = RT 2 (∂ln σ / ∂T ) E a = RBT 2 /( T − T V ) 2 − RT /2 …”

“…The system was then cooled down to 293 K. Afterwards, the sample was heated up again to 413 K with temperature interval of 1 K. The detailed operation process can be found in ref. 41 .…”