Mass Spectrometric Study of the Reactions of BF3(g) with BCl3(g), B(OH)3(g), and B2O3(1)

Abstract

Exchange reactions of halogen and hydroxyl with BX₃(g) have been studied mass spectrometrically. The major product produced by the reaction of BF₃(g) with boric acid at 25°C and pressures of the order of 10^—6 atm is B(OH)F₂(g). The species B(OH)₂F(g) is also formed at higher temperatures when B(OH)₃(g) is observable. Equilibria involving the reactions $$\begin{array}{c}\frac{1}{3}{\mathrm{BF}}_3(\mathrm{g}\mathrm{)+}\frac{2}{3}{\mathrm{BCl}}_3(\mathrm{g}\mathrm{)=}{\mathrm{BFCl}}_2(\mathrm{g}\mathrm{),}\\ \frac{2}{3}{\mathrm{BF}}_3(\mathrm{g}\mathrm{)+}\frac{1}{3}{\mathrm{BCl}}_3(\mathrm{g}\mathrm{)=}{\mathrm{BF}}_2\mathrm{Cl}(\mathrm{g}\mathrm{),}\\ \frac{1}{3}{\mathrm{BF}}_3(\mathrm{g}\mathrm{)+}\frac{2}{3}\mathrm{B}(\mathrm{OH}{)}_3(\mathrm{g}\mathrm{)=}\mathrm{B}(\mathrm{OH}{)}_2\mathrm{F}(\mathrm{g}\mathrm{),}\end{array}$$ and $$\frac{2}{3}{\mathrm{BF}}_3(\mathrm{g}\mathrm{)+}\frac{1}{3}\mathrm{B}(\mathrm{OH}{)}_3(\mathrm{g}\mathrm{)=}\mathrm{B}(\mathrm{OH}){\mathrm{F}}_2(\mathrm{g}\mathrm{),}$$ have been studied as a function of temperature. Heats of formation at 298°K for BFCl₂(g), BF₂Cl(g), B(OH)₂F(g), and B(OH)F₂(g) are found to be —154.1±1.0, —211.9±2.0, —249.8±2.5, and —260.2±2.5 kcal/mole, respectively. Reactions of BF₃(g) with B₂O₃(l) have also been studied at pressures between 10^—6 and 10^—3 atm and temperatures between 400 and 1000°K. Results are consistent with published data from studies with BF₃ at pressures near 1 atm and show that (BOF)₃(g) is the primary product at both pressure extremities. For the reaction $${\mathrm{BF}}_3(\mathrm{g}\mathrm{)+}{\mathrm{B}}_2{\mathrm{O}}_3(\mathrm{l}\mathrm{)=(}\mathrm{BOF}{)}_3(\mathrm{g}\mathrm{),}$$ we obtain ΔH_T°=3.46±0.30 kcal/mole.