A Simple Method for the Preparation of ۲,۴,۶-trichloroborazine and Evaluation of ۱H-NMR Spectra

The compound ۲,۳,۶-trichloroborazine (TCB) is known as a valuable precursor to prepare boron nitride and various derivatives of borazine. Difficulties in the preparation of TCB via conventional methods on the one hand, and its importance for material science, on the other hand, were our motivations to modify Brown’s method for TCB synthesis. So far, all reports on the synthesis procedure of TCB are based on the use of gaseous BCl۳ with NH۴Cl powder at ۱۱۰-۱۳۰ °C in chlorobenzene requiring complicated low-temperature equipment such as a cold finger condenser, and dry ice-acetone reflux condenser to retain BCl۳ gas in the reaction flask. According to our study, using BCl۳ solution in n-hexane was more convenient than using gaseous BCl۳. The reaction of BCl۳ solution with NH۴Cl was carried out without loss of BCl۳. Furthermore, the reduction in the reflux temperature from ۱۳۰ °C in some previous studies to ۸۶ °C in our study, was a valuable advantage, leading to the release of the coordinated BCl۳ from the adduct complex [CH۳CN·BCl۳] gradually and the prevention of thermal decomposition of TCB, unwanted polymerization reactions and the formation of undesirable products, resulting in the increased reaction yield. TCB was fully characterized by ATR-FTIR, ۱۱B-, ۱۴N-, and ۱H-NMR spectroscopic methods. ۱H-NMR spectra of TCB were performed for the first time at various temperatures to elucidate the quadrupole effect of nitrogen, leading to the observation of the proton resonance splitting of the ۱۴N-H bond by coupling with the ۱۴N quadrupole nucleus. The broad peak observed at room temperature was clearly split into a triplet at ۱۰۰ °C due to the long TqN and fast molecular motion of TCB molecules. The ۱۴N-NMR spectrum was also shown for the first time as a broad signal at δ = –۲۷۱.۳ ppm (h۱/۲ = ۱۸۶ Hz).

کلیدواژه ها:

Borazine derivatives ، Adduct complex ، NMR-Spectroscopy ، Quadrupole effect ، Boron trichloride