New Synthesis and Nitration of 1,2-Bis(5-aminotetrazol-1-yl)ethane

Abstract

Tetrazole derivatives, which have high nitrogen content, belong to an interesting class of heterocycles that could be applied to a variety of high energy density materials (HEDMs). Particularly, aminotetrazole-based energetic materials have attracted considerable interest due to their high thermal stabilities and large positive heats of formaton. Moreover, they are anticipated to be quite insensitive, extremely powerful, and produce less pollutants when explode. Recently, 1,2-bis(5-nitroiminotetrazol-1-yl)ethane (3) and its energetic salts have been prepared in good yields (Scheme 1). The development of 1,2-bis(5-aminotetrazol-1yl)ethane (2) has been extended by the utilization of an excellent in situ method that involves reactions of cyanogen azide and ethylene diamine. Nitration of aminotetrazole 2 using 100% nitric acid produced 3. The synthesis of nitroiminotetrazole salts provided a straightforward approach to highly energetic salts, which exhibit attractive physical properties, such as good thermal stabilities, high densities, and good heats of formation. 1-Substituted 5-aminotetrazole derivatives were prepared by the treatment of potassium 5-aminotetrazolate with an alkyl halide. There are several reports in the literature describing in situ generation of 1-substituted 5-aminotetrazoles via alkylation of 5-aminotetrazole with alkyl halides. However, selective alkylation of aminotetrazoles is not possible because of the competitive formation of 1and 2alkylated-5-aminotetrazoles. These isomers were separable in very low yields by crystallization or column chromatography. 1-Substituted 5-aminotetrazoles could be efficiently prepared using cyanogen azide. However, cyanogen azide is highly toxic and is not convenient to handle. In this work, we present a new synthetic scheme for compound 2 without using toxic cyanogen azide and introduce an efficient preparation of 3 for easy scale-up. The synthesis of 2 results from a nucleophilic substitution reaction between 2 equivalent of sodium 5-aminotetrazolate and 1 equivalent of 1,2-dibromoethane (Scheme 2). However, three isomers, 2, 1-(5-aminotetrazol-1-yl)-2-(5-aminotetrazol-2-yl)ethane (6), and 1,2-bis(5-aminotetrazol-2-yl)ethane (ratio = 1:3:1), from this reaction were formed as was reported in the literature. Separation of the three isomers was accomplished based on the difference of aqueous solubility. 2 was isolate in 11% yield through a very rapid filtration from refluxing suspension with a small amount of water. To improve the yield, we searched for a new route for compound 2. 1-(2-Chloroethyl)-5-aminotetrazole (5) can be prepared by chlorination of 1-(2-hydroxyethyl)-5-aminotetrazole, which was synthesized from sodium 5-aminotetra-