Synthesis Of Precursor Of Hexagonal Boron Nitride (h-BN)

With boron trichloride (BCl₃) and ammonium chloride (NH₄Cl) as raw materials and chlorobenzene (C₆H₅Cl) as solvent, high purity crystal B-trichloroborazine (TCB) was synthesized and purified through vacuum line technique which was modified from standard Schlenk technique to suit for synthesis of TCB. The precursor of hexagonal boron nitride (h-BN), B-dimethylamineborazine, was then obtained by substitution of TCB with alkyl amine ((CH₃)₂NH), from which high quality BN could be obtained.The reaction process was simulated employing B3LYP/6-31G^* basis set in GAUSSIAN2003 series program. Structure optimization and energy analysis of the TCB molecule and its substituents were carried out. IRC calculation of the TCB substitution reactions was also performed. It is found that the reactivity of TCB and its substituents are in the following order: TCB>[N(CH₃)₂]₃B₃N₃H₃>Cl[N(CH₃)₂]-2B-3N₃H₃>Cl₂[N(CH₃)₂]B₃N₃H₃. The results also show that the intermediate state of the substitution contains a Cl-B-N-H-Cl tetratomic ring. It can be further postulated from the simulation that a mixture of several different products could exist in the reaction.The conditions, apparatuses and the route of reactions were examined, and the results were analyzed using NMR. XRD analysis of TCB was also performed. It is found that the synthesis follows a homogeneous liquid phase reaction mechanism. The yield of TCB can go up to above 89% when Hg was used as catalyst or above 87% by proper extending of the reaction time when no catalyst used. The optimum theoretical plate numbers of rectification column is about 6 during purification.