Synthesis and energetics of Na, K, Rb and Cs salts by reaction with 1,2-ethanediol and 1,4-butanediol

The study of direct reactions of Na, K, Rb and Cs with 1,2-ethanediol and with 1,4-butanediol was undertaken as well as the reactions of Na and K with 1,2-ethanediol by an ammoniacal route. All compounds were characterized by standard elemental analysis techniques, thermogravimetric analysis (TGA) and infrared (IR) spectroscopy. The results show that only one hydroxyl group reacts with the metal leading to the formation of compounds of the type M(OC2H4OH) or M(OC4H8OH), where M stands for the alkaline metal, except for the reaction of Cs with 1,2-ethanodiol that points to the formation of an adduct, Cs(OC2H4OH).HOC2H4OH. The standard enthalpies of formation of the alkaline metal diolates in the crystalline state were determined by reaction-solution calorimetry. The obtained results at 298.15 K were as follows: ΔfHmo (MOCxH2xOH, cr)/kJ⋅mol−1 = −589.46.0 (NaOC2H4OH), −654.28.3 (NaO-n-C4H8OH), −615.17.4 (KOC2H4OH), −679.97.7 (KO-n-C4H8OH), -609.83.1 (RbOC2H4OH), and −1091.4 ± 6.3 (CsOC2H4OH·HOC2H4OH). These results were compared with the literature values for other alkoxides and together with auxiliary values were used to derive a consistent set of lattice energies for MOCxH2xOH compounds based on the Kapustinskii equation. This allows the estimation of the enthalpy of formation for some non-measured diolates.