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The solubilities of disodium cyclooctatetraeneide and dipotassium cyclooctatetraeneide have been accurately determined in hexamethylphosphoramide (HMPA) and tetrahydrofuran (THF) as a function of temperature. For the THF systems the dianion was considered to exist as a quadruple ion (associated with two cations) as previously reported, and the enthalpies of solution were found to be 1.09 and 5.13 kcal/mol for the potassium and sodium salts, respectively. The fact that AH°of solution is positive indicates that the crystal lattice energies are larger than the solvation energies of the quadruple ions. In HMPA the dianion was considered to exist as a free ion. However, considerable curvature was observed in a plot of In Ksp vs. 1/RT. This curvature was attributed to the formation of ion pairs between the cyclooctatetraene (COT) dianion and one potassium cation. Addition of KI to solutions of the COT dianion and anion radical in HMPA shift the observed reverse disproportionation (comproportionation) equilibrium constant to smaller values confirming the formation of ion pairs. The sodium salt did not exhibit curvature in the van't Hoff plot, and the comproportionation equilibrium constant was invariant with the addition of NaClOs to solutions of the COT dianion and anion radical in HMPA.

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