Safety improvement of chemical processes involving azides by online monitoring of the hydrazoic acid concentration

Hydrazoic acid (HN3) is formed during the synthesis of tributyltin azide and in the following cycloaddition to prepare a tetrazole ring compound. The formation of this substance is inherent to many azide processes because small amounts of protic components cannot be avoided. Hydrazoic acid is a very toxic volatile compound, which has highly explosive properties. Under certain conditions (presence of impurities in the reaction mixture), the gas concentration can come close to the decomposition limit. Therefore, online monitoring of this gas concentration is essential to ensure the process safety. FT-IR and FT-NIR experiments were performed in the laboratory scale to calibrate the spectrometers. Due to the possibility of using quartz light fiber cables, a FT-NIR spectrometer was installed to monitor the hydrazoic acid concentration in the industrial scale.