The effect of position and length of alkyl substituents in pyridinium based ionic liquids on temperature dependent transport properties

Abstract

The effect of position and length of alkyl substituent in pyridinium based ionic liqs. (IL) has been studied at various temps. The IL investigated contained the bis(trifluoromethanesulfonyl)imide (NTf2) anion combined with 1-alkyl-3,5-dimethylpyridinium or 1-alkyl-2,3-dimethylmpyridinium cations, resp. Data for the cond. 0-80 °C, the viscosity 10-70 °C, d. 0-80 °C and thermal expansion coeffs. 0-80°C of the ionic liqs. [B23MMPYR][NTf2], [B35MMPYR][NTf2], [O23MMPYR][NTf2], [O35MMPYR][NTf2] are reported. The viscosity and cond. data obtained could be well described with the empirical Vogel-Fulcher-Tammann equation. Based on the molar conductivities and viscosities measured from 10 to 70 °C, a significant influence of the position of the Me substituents in the cation on the transport properties has been found. Walden plots of these data demonstrate that the investigated compd. can be classified as high ionicity ionic liqs. IL contg. 1-alkyl-2,3-dimethylpyrindium cations were found to be closer to the "ideal" KCl line suggesting less ion assocn. compared to their 1-butyl-3,5-dimethylpyridinium homologues.