Opportunities and Limits of the Use of Azides in Industrial Production. Implementation of Safety Measures

Abstract

Azides are very versatile precursors of organic synthesis functionalities such as amines, isocyanates, sulfonamides, triazoles, tetrazoles, triazolines, aziridines, amino acids and diazo compounds. In industry, one of the favourite starting materials for these syntheses is sodium azide which can generate hydrazoic acid whose toxicity and detonation potential is of major safety concern. However sodium azide is used daily in large tonnage in the air-bags of vehicles, in biologic institutes as a bactericide and in agriculture as a herbicide. In industrial synthesis, sodium azide is actually the starting material of herbicides, anti-HIV pharmaceuticals, anti-pain compounds and hypo tensors. This massive use of sodium azide represents severe toxicological and physical damage risks. The industrial synthesis under the scope of this presentation will be the manufacture of a tetrazole produced in several tens of tons per year. A risk assessment concluded that it would be necessary to conduct the reaction in a 'Bunker' and to minimise risks by absolutely avoiding generation of hydrazoic acid. This can be achieved by a careful design of the process and by strict organisational measures. Furthermore, the reaction equipment was designed to prevent any condensation of hydrazoic acid. One way to prevent its formation is to maintain the reaction medium under basic conditions at all times. This is achieved by using triethylamine hydrochloride as a buffer. In the applied reaction conditions it could be demonstrated that triethylamine was the refluxing compound at 130 °C and that a thermally stable triethyl ammonium azide was formed. The environmental problem could be resolved by incineration of the wastewaters. In conclusion, reactions with sodium azide are safe, they only need a stabilising agent. A search for such compounds could be an interesting but rather dangerous research project.