abstract
Vapor pressures of 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide, ([C(1)C(1)im][NTf2]) and 1ethyl-3-propylimidazolium bis(trifluoromethylsulfonyl) imide, ([C(2)C(3)im][NTf2]) ionic liquids were measured as a function of temperature using a Knudsen effusion apparatus combined with a quartz crystal microbalance. Enthalpies and entropies of vaporization were derived from the fitting of vapor pressure and temperature results to the Clarke and Glew equation. [C(1)C(1)im][NTf2] presents a higher enthalpy and entropy of vaporization than the neighboring members of the series. The enthalpy of vaporization of [C(2)C(3)im][NTf2] lies in between the asymmetric and symmetric ionic liquid series, reflecting a decrease in the electrostatic interactions due to a decrease of the charge accessibility between the ionic pairs when the methyl group is replaced by an ethyl group. The obtained higher volatility of [C(2)C(3)im][NTf2] arises from its asymmetric character, leading to an higher entropic contribution that compensates the enthalpic penalty. The border conditions ([C(1)C(1)im][NTf2], [C(2)C(1)im][NTf2] and [C(2)C(2)im][NTf2]), topology ([C(2)C(3)im][NTf2]) and symmetry/asymmetry of the ILs effect were evaluated and rationalized based on a comparative analysis of the thermodynamic properties, enthalpies and entropies of vaporization. (C) 2013 Elsevier Ltd. All rights reserved.
keywords
THERMODYNAMIC PROPERTIES; CONFORMATIONS; CONSTANTS
subject category
Thermodynamics; Chemistry
authors
Rocha, MAA; Ribeiro, FMS; Schroder, B; Coutinho, JAP; Santos, LMNBF
our authors
Bernd Schroder
Post-doc Fellowship
acknowledgements
Thanks are due to Fundacao para a Ciencia e Tecnologia (FCT), Lisbon, Portugal and to FEDER for financial support to Centro de Investigacao em Qu mica, University of Porto through the project Pest-C/QUI/UI0081/2011, and CICECO, University of Aveiro, through the project Pest-C/CTM/LA0011/2011. Marisa A. A. Rocha and Bernd Schrder acknowledges the financial support from FCT and the European Social Fund (ESF) under the Community Support Framework (CSF) for the award of a Ph. D. Research Grants SFRH/BD/60513/2009 and a Post-Doctoral Grant, SFRH/BPD/38637/2007, respectively.