By means of the in-situ Fourier transformation infrared spectroscopy（FTIR）, the properties of BBr3/ benzene solution, which is usually used as the reactant and solution to synthesize BN by benzene-thermal method, have been investigated. The results show that there are some side reactions between BBr3 and benzene： （1） BBr3 as an electron-deficient molecule reacts with benzene at room temperature; （2） below 100℃, substitution of Br atom for H atom of benzene（ring-H） dominates in BBr3/benzene solution; （3） cracking of benzene ring occurs at a temperature above 100℃; （4） decomposition of benzene molecules and formation of long-chain aliphatic compounds feature the spectra of BBr3/benzene solution collected at above 160℃, They are unfavor for BN to form when BBr3 is excessive in the synthesis of BN by benzene-thermal route. On the basis of the experimental results, a coordination reaction mechanism via a η^2-C6H6 binding mode in BBr3/benzene solution is suggested.
