Temperature Dependence of Association Constants of LiAlCl₄ in Liquid Sulfur Dioxide

Robert Hartl,¹ Roland Neueder² and Heiner J. Gores^1,*

¹ University of Regensburg, Institute for Theoretical and Physical Chemistry, Workgroup Electrochemistry and Electrolytes, 93053 Regensburg, Germany
² University of Regensburg, Institute for Theoretical and Physical Chemistry, 93053 Regensburg, Germany
* Corresponding author: E-mail: heiner.gores@chemie.uni-regensburg.de

Abstract
In this work the conductivities of LiAlCl₄ in dilute sulfur dioxide solutions were measured in the temperature range 238.15 K to 288.15 K. The major challenge of these measurements was the handling of the very water sensitive salt LiAlCl₄ and the formulation of sulfur dioxide solutions at low salt concentrations. These low concentration solutions are needed to obtain association constants of the salt and thermodynamic parameters using the low concentration chemical model developed by J. Barthel. The viscosities of liquid sulfur dioxide were also measured in the temperature range 231.46 K to 257.98 K. Unexpectedly, the determined association constants of LiAlCl₄ in liquid sulfur dioxide are very small ranging from 42 at 238.15 K to 354 dm³ mol^–1 at 288.15 K. This result shows that the lithium-ion solvent interaction is much stronger when compared with the interaction of the lithium-ion with the weakly coordinating anion tetrachloroaluminate, in contrast to lithium halides in liquid sulfur dioxide where association constants up to 96000 dm³ mol^–1 are observed.

Keywords: Non aqueous solutions, electric conductivity, lithium tetrachloroaluminate, ion association, sulfur dioxide