Thermal decomposition of cyclotriborazane

Cyclotriborazane (CTB), B3N3H12, is a crystalline white solid, which decomposes above 400 K to hydrogen and a few other products, depending on the reaction conditions. In this work we present investigations of the thermal decomposition of both the neat compound and CTB dissolved in diglyme and tetraglyme. Several thermophysical and analytical methods, such as differential scanning calorimetry (DSC), thermogravimetry (TG), mass spectroscopy (QMS), and 11B nuclear magnetic resonance spectroscopy (NMR) have been used for this investigation. The decomposition of the neat substance releases 3.1 mol H2/mol CTB and leads to a polymeric products and borazine. In open vessels, sublimation as a competing process also occurs. The enthalpy of the decomposition process (ΔRHs) has been determined as ΔRHs = −34.0 ± 2.9 kJ/mol. In contrast to the thermal decomposition of the pure substance, the decomposition in polyethers, such as diglyme and tetraglyme, leads above 370 K to borazine and small amounts of soluble oligomeric borazine species. Also BH3 group containing species are occurring as intermediates. In these systems no precipitation was detected. DSC measurements show for the decomposition in solution several strong exothermic effects. The overall decomposition enthalpy in diglyme is given by ΔRHd = −32.0 ± 2.8 kJ/mol and in tetraglyme by ΔRHt = −48.0 ± 4.7 kJ/mol. The enthalpy of solution of cyclotriborazane was determined in diglyme and in tetraglyme with the values ΔDHd = −2.1 ± 0.2 kJ/mol and ΔDHt = −4.6 ± 0.5 kJ/mol, respectively.