5-azido-1H-tetrazole - Improved synthesis, crystal structure and sensitivity data

Due to the highly explosive nature of 5-azido-1H-tetrazole (1), its characterization has not been fully described in the literature yet. In addition, the previously published crystal structure was of low quality, and therefore the position of the hydrogen atom was not certain. In order to resolve these problems, 1 was prepared in an improved synthesis, and the results of the subsequent detailed reinvestigation and characterization are given. The reaction of cyanogen bromide with two equivalents of sodium azide at low temperatures yielded sodium 5-azidotetrazolate, which was protonated using dilute hydrochloric acid. The product 1 was isolated and characterized using multinuclear (H-1, C-13, N-15) NMR spectroscopy, vibrational (IR and Raman) spectroscopy and mass spectrometry. The structure of 1 in the crystalline state was determined using low-temperature single-crystal X-ray diffraction. In addition, the optimized gas-phase structures of the 5-azido-1H-tetrazole and 5-azido-2H-tetrazole isomers were calculated (MP2/aug-cc-pVDZ) and the electronic energies were compared. The heat of formation of 1 was calculated and several detonation parameters were estimated using the EXPLO5 software. The thermal behavior was investigated using DSC (differential scanning calorimetry) and the sensitivity of this highly energetic material was tested using the BAM drophammer, ESD and friction tester. X-ray: 1: monoclinic, P2(1/c), a = 13.265(2) angstrom, b = 4.9693(6) angstrom, c = 16.304(3) angstrom, beta = 127.04(1)degrees, V = 857.9(3) angstrom(3), Z = 8, p = 1.720 g cm(-3).