Gaseous Metaborates. I. Mass-Spectrometric Study of the Vaporization of Lithium and Sodium Metaborates

The vaporization of lithium and sodium metaborate has been studied mass spectrometrically. The vapors of these compounds consist principally of the monomers LiBO₂ and NaBO₂, with some dimer and a very small amount of trimer also present. Heats of vaporization of the two metaborates and of boron oxide were determined with an effusion cell designed to give reliable second‐law heats. The values obtained are: $$\begin{array}{cc}{\mathrm{B}}_2{\mathrm{O}}_3(\mathrm{l}\mathrm{)=}{\mathrm{B}}_2{\mathrm{O}}_3(\mathrm{g})& {\mathrm{\Delta H}}_{\text{v,1300}}\text{=93.6±3\hspace{0.17em}}{\mathrm{kcal\; mole}}^{\text{−1}}\\ {\mathrm{LiBO}}_2(\mathrm{c}\mathrm{)=}{\mathrm{LiBO}}_2(\mathrm{g})& {\mathrm{\Delta H}}_{\text{s,1060}}\text{=79±3\hspace{0.17em}}{\mathrm{kcal\; mole}}^{\text{−1}}\\ {\mathrm{LiBO}}_2(\mathrm{l}\mathrm{)=}{\mathrm{LiBO}}_2(\mathrm{g})& {\mathrm{\Delta H}}_{\text{v,1160}}\text{=70±3\hspace{0.17em}}{\mathrm{kcal\; mole}}^{\text{−1}}\\ \text{2\hspace{0.17em}}{\mathrm{LiBO}}_2(\mathrm{g}\mathrm{)=}{\mathrm{Li}}_2({\mathrm{BO}}_2{)}_2(\mathrm{g})& {\mathrm{\Delta H}}_{1120}\text{=−67±3\hspace{0.17em}}{\mathrm{kcal\; mole}}^{\text{−1}}\\ {\mathrm{NaBO}}_2(\mathrm{c}\mathrm{)=}{\mathrm{NaBO}}_2(\mathrm{g})& {\mathrm{\Delta H}}_{\text{s,1070}}\text{=73±3\hspace{0.17em}}{\mathrm{kcal\; mole}}^{\text{−1}}\\ \text{2\hspace{0.17em}}{\mathrm{NaBO}}_2(\mathrm{g}\mathrm{)=}{\mathrm{Na}}_2({\mathrm{BO}}_2{)}_2(\mathrm{g})& {\mathrm{\Delta H}}_{1070}\text{=−53±3\hspace{0.17em}}{\mathrm{kcal\; mole}}^{\text{−1}}.\end{array}$$ The composition and the dimerization energies of the metaborate vapors thus resemble those of the alkali halides, hydroxides, and cyanides.