Potentiometric Studies of the Chlorine Electrode in Ambient-Temperature Chloroaluminate Ionic Liquids: Determination of Equilibrium Constants for Tetrachloroaluminate Ion Dissociation

摘要

The potentiometric behavior of the chlorine electrode has been investigated at 40 C in aluminum chloride-N--butylpyridinium chloride and in aluminum chloride-1-methyl-3-ethylimidazolium chloride ionic liquids. In basic (excess organic chloride) melts, the Nernstian behavior of a tungsten electrode in solutions containing Cl2(g) indicates two electrode reaction stoichiometries: Cl3(-) + 2e- = 3Cl(-), when chloride ion is in excess over chlorine, and 3 Cl2 + 2e-, when there is an excess of chlorine. Formal potentials of the C12/C13(-), Cl3(-)/Cl(-), and Cl2/Cl(-) couples have been determined in both ionic solvents, and the stability constant for the Cl3(-) ion has been obtained. The difference between the E superscript 0 (Cl3(-)) values in these two solvents reflects the difference between ionic association constants for the two organic chlorides. In acidic (excess AlCl3) melt compositions, slow equilibria and reactions of chlorine with the organic cations impede potentiometric measurements with the chlorine electrode. The reversible chlorine electrode potential could be measured only in acidic AlCl3-BuPyCl melts, and the tetrachloroaluminate ion dissociation constant has been obtained. Keywords: Molten salts; Fused salts.