Thermodynamic Characteristics of Lithium Pivalate according to High-Temperature Mass Spectrometry Data

Abstract

The vaporization of lithium pivalate (CH₃)₃CCOOLi (LiPiv) was studied by the Knudsen effusion method with the mass spectral analysis of the gas phase. The saturated vapor consisted of polynuclear molecules (LiPiv)_n, dominated by (LiPiv)₂ and (LiPiv)₄ molecules. The absolute values of the partial pressures of these molecules and their dependence on temperature were calculated. The standard enthalpies of sublimation of the main components of the saturated vapor were determined to be ${{\Delta }_{s}}H_{{298}}^{^\circ }$(LiPiv)₂ = 174.2 ± 6.6 kJ/mol and ${{\Delta }_{s}}H_{{298}}^{^\circ }$(LiPiv)₄ = 195.7 ± 4.5 kJ/mol. The enthalpies of dissociation of the dimeric molecules into the monomeric molecules and of the tetrameric molecules into the dimeric molecules were calculated by the second and third laws of thermodynamics; the average values of these enthalpies are ${{\Delta }_{D}}H_{{298}}^{^\circ }$(LiPiv)₂ = 175.8 ± 13.5 kJ/mol and ${{\Delta }_{D}}H_{{298}}^{^\circ }$(LiPiv)₄ = 155.2 ± 10.0 kJ/mol. The standard enthalpies of formation of LiPiv in the condensed and gas phase were estimated from the known thermodynamic characteristics of lithium acetate and radicals of acetic and pivalic acids: ${{\Delta }_{f}}H_{{298.15}}^{^\circ }$(LiPiv_solid) ≤ –804 kJ/mol, ${{\Delta }_{f}}H_{{298.15}}^{^\circ }$(LiPiv_gas) ≤ –627 kJ/kmol, ${{\Delta }_{f}}H_{{298.15}}^{^\circ }$((LiPiv)_2(gas)) ≤ –1430 kJ/mol, and ${{\Delta }_{f}}H_{{298.15}}^{^\circ }$((LiPiv)_4(gas)) ≤ –3017 kJ/mol.