Caution: Tetrazene is a primary explosive and must be handled with care. Safety precautions for handling explosives must be followed.
3.1. Synthesis
Synthesis of tetrazene A form: Tetrazene was prepared according to guidelines in [
14]: Sodium nitrite (7.50 g; 109 mmol) and bisaminoguanidinium sulfate (8.75 g; 35.5 mmol) were dissolved in water (100 mL). The solution was then acidified with acetic acid at 25 °C to obtain pH 5.4 and the mixture was stirred at 56–58 °C for an extended time (see
Section 2.2). After cooling to room temperature, the solid precipitate was filtered and washed gradually with water, ethanol and finally acetone, yielding 4.35 g (65.1%) of final product.
Tign. = 140 °C (DTA). Anal. Calc. for C
2H
8N
10O (%): C 12.77, H 4.29, N 74.44. Found: C 12.76, H 4.15, N 73.86. FTIR (cm
−1): 3308 m, 3262 sh, 3154 m, 2977 m, 1699 m, 1625 m, 1533 m, 1482 s, 1442 w, 1413 s, 1271 m, 1202 w, 1155 s, 1104 w, 1091 m, 1080 w, 1068 s, 1039 m, 952 m, 848 sh, 807 w, 770 sh, 754 s, 725 s, 659 s. Raman (cm
−1): 1532 w, 1497 m, 1490 m, 1441 s, 1416 s, 1203 w, 1159 w, 1101 w, 1094 w, 1073 m, 1039 vw, 956 w, 785 m, 714 vw, 614 vw, 518 w, 464 w, 426 w, 294 w. Both vibrational spectra are fully disclosed in
Supplementary Materials.
Synthesis of tetrazene C form: Tetrazene C was prepared according to the procedure of preparation tetrazene A (above), with reaction time shortened to 35 min after the precipitation is initiated. The yield of C form was 5.03 g (75.3% of theory).
Tign. = 137 °C (DTA). Anal. Calc. for C
2H
8N
10O (%): C 12.77, H 4.29, N 74.44. Found: C 12.47, H 4.20, N 73.69. To obtain pure C form the reaction is carried out at 40 °C for 4 h. FTIR and Raman spectra are reported in
Table 1 in the Results and Discussion section and
Supplementary Materials.
Synthesis of tetrazene-
15N
1 C form: Isotope labeled tetrazene C form-
15N
1 (5-[(1
E)-3-amidiniotetraz-1-en-1-yl](2-
15N)tetrazolide hydrate,
Figure 4) was prepared according to the modified procedure described in [
24] using sodium nitrite-
15N (Aldrich, purity 95%, 98%
15N): 5-aminotetrazole hydrate (0.515 g, 5.00 mmol) and aminoguanidine nitrate (0.685 g, 5.00 mmol) were dissolved in water (35 mL) at room temperature and sodium nitrite-
15N (0.400 g, 5.70 mol) in water (3 mL) was added. A yellow turbid liquid was formed and the mixture was stirred at 24 °C for three hours. The precipitate was filtered and washed with water and ethanol yielding 0.220 g of solid (23.3%).
Tign. = 135 °C (DTA). FTIR and Raman spectra are reported in
Table 1 in the Results and Discussion section and
Supplementary Materials.
Synthesis of tetrazene-
15N
2 C form: Isotope labeled tetrazene C form-
15N
2 (5-[(1
E)-3-amidinio(2-
15N)tetraz-1-en-1-yl](2-
15N)tetrazolide hydrate,
Figure 4) was prepared via the procedure used to prepare tetrazene A which was downscaled and using sodium nitrite-
15N (Aldrich, purity 95%, 98%
15N) obtained tetrazene-
15N
2 in A form (yield 74.5%). Form A was transformed to tetrazene-
15N
2 in C form by the following modified procedure described in [
20,
25]: Tetrazene in A form (0.056 g) was dissolved in 65% nitric acid (5 mL) and the solution was poured into water (200 mL). Dilute ammonia solution was then used to raise the pH value to 6 (precipitation of tetrazene started slowly at pH 0.5 and by 1.5 the process was complete). The resulting solid was filtered, washed gradually with water, ethanol and acetone, yielding 0.020 g (35.7%) form C tetrazene.
Tign. = 132 °C (DTA). FTIR and Raman spectra are reported in
Table 1 in the Results and Discussion section and
Supplementary Materials.
Tetrazene C form single crystalline material: The preparation of a single tetrazene crystal suitable for X-ray analysis was as follows: Sodium nitrite (6 g; 87.0 mmol) and bisaminoguanidinium sulfate (7 g; 28.4 mmol) were dissolved in water (100 mL). Acetic acid was used to adjust the pH to the initial value range of 5.2–5.7. The mixture was then left undisturbed at laboratory temperature. The following day large orange-yellow crystals were found (
Figure 8c). The mixture remains active and after a week further product can be obtained; at least a total of 3.5 g (70.7%) of product is obtainable.
3.2. Measuring Tmethods
pH measurement: The reaction mixture pH was measured using Schott Instruments Lab 850 pH meter (Mainz, Germany) equipped with SI Analytics pH electrode BlueLine 14 pH (Mainz, Germany). Fisher Scientific pH 4.00, 7.00 and 10.00 buffer solutions were used for three-point calibration of the electrode.
DTA: Differential thermal analysis was carried out with a DTA 550 Ex thermal analyzer produced by OZM Research (Hrochův Týnec, Czech Republic). The samples were tested in open glass micro-test tubes in contact with air. The weight of samples was 3–5 mg, the heating rate was 5 °C∙min−1. Decomposition of tetrazene was accompanied by a strong acoustic effect and the destruction of the micro-test tube.
DSC: Differential scanning calorimetry was carried out with a DSC thermal analyzer DSC Q2000 produced by TA Instruments (New Castle, DE, USA). Measurements were performed at a heating/cooling rate of 20 °C∙min–1 in closed aluminium sample pans with a hole on the top for gas release, with a nitrogen flow of 50 mL∙min–1.
Elemental analysis: it was carried out using automatic elemental analyzer UNICUBE (Elementar, Langenselbold, Germany) on 1–2 mg samples.
FTIR: Infrared spectra were collected using a Nicolet iS50 FT-IR spectrometer (Thermo, Madison, WI, USA) with an ATR single reflection ZnSe accessory GladiATR (PIKE, Fitchburg, WI, USA). Measurement parameters were: spectral region 4000–600 cm−1, resolution 4 cm−1 and number of scans 64 (for isotopically labeled materials the resolution was 1 cm−1 and number of scans 128).
Raman spectroscopy: Raman spectra were measured using the Nicolet iS50 Raman module. Excitation laser 1064 nm, power of laser 50–500 mW, with defocusing lens to avoid rapid sample decomposition, spectral region 4000–100 cm−1, resolution 4 cm−1 and number of scans 96. Spectral manipulation for both, infrared and Raman, spectra was done using Omnic 9.2 software.
X-ray analysis: Full-sets of diffraction data for tetrazene were collected at 150(2) K and 293(2) K, respectively, with a Bruker D8-Venture diffractometer equipped with Mo (Mo/Kα radiation; λ = 0.71073 Å) microfocus X-ray (IµS) sources, Photon CMOS detector and Oxford Cryosystems cooling device was used for data collection. The frames were integrated with the Bruker SAINT software package using a narrow-frame algorithm. Data were corrected for absorption effects using the Multi-Scan method (SADABS). Resulting data were treated by XT-version 2014/5 and SHELXL-2017/1 software implemented in APEX3 v2016.5-0 (Bruker AXS) system [
26]. Hydrogen atoms were localized on a difference Fourier map. Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 2103722. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EY, UK (fax: +44-1223-336033; e-mail:
[email protected] or www:
http://www.ccdc.cam.ac.uk, accessed on 17 August 2021).
The diffraction data were collected at room temperature with an X’Pert3 Powder θ-θ powder diffractometer with parafocusing Bragg-Brentano geometry using Cu Kα radiation (λ = 1.5418 Å, Ni filter, generator setting: 40 kV, 30 mA). An ultrafast PIXCEL detector with 255 channels was employed to collect XRD data over the angular range from 5 to 80° 2θ with a step size of 0.026° 2θ and a counting time of 0.618 s/step. The software package HighScore Plus V 4.8 (PANalytical, Almelo, Netherlands) was used to smooth the data, to fit the background, to eliminate the Kα2 component, and the top of the smoothed peaks were used to determine the 2θ peak positions and intensities (I-values) of the diffraction peaks. The d-values were calculated using the Bragg law and Cu Kα1 radiation (λ = 1.5406 Å).
SEM: Samples of tetrazene were visualized with a scanning electron microscope (SEM; Jeol JSM 5500 LV) (JEOL, Akishima, Japan).
Sensitivity measurement: Sensitivity to friction was determined using small BAM apparatus type FSA-12. The testing set consisted of porcelain BFST Pt 100 25 × 25 mm plates and BFST Pn 200 pegs. Sensitivity to impact was measured using BAM fall hammer. Testing sets composed of steel guides BFH-SC and cylinders BFH-SR. All sensitivity measurement apparatus and related supplies were manufactured by OZM Research (Hrochův Týnec, Czech Republic). Sensitivities to friction and impact were evaluated using probit analysis on 15 trials on each intensity level (at least five levels where possible) and results were expressed as a friction force or impact energy with 50% probability of initiation [
27].
Performance of priming mixtures: Priming mixtures containing tetrazene A or C and functionality of final primers was determined in primers force test (Lachaussée s.a. type 765/60-64). Priming mixtures NEROXIN F (containing lead styphnate/tetrazene/Ba(NO3)2/Sb2S3/PbO2/Pb3O4), NEROXIN PX (containing lead styphnate/tetrazene /Ba(NO3)2/Sb2S3/PbO2/Pb3O4/pentaerythritol tetranitrate) and NONTOX (tetrazene/pentaerythritol tetranitrate/KNO3/boron/ glass powder/nitrocellulose) were prepared using standard production technology from the Sellier&Bellot company for both forms of tetrazene. The primer type 4.4 SP was used for NEROXIN F composition, type 5.3 LR for NEROXIN PX and type 4.4 SP Nontox for NONTOX composition. The completed primers were fitted into closed manometric vessels containing dynamic pressure sensor model 102B03 (PCB Piezotronics Inc.). The primers were initiated by the fall of a 112 g ball from a height of 30 cm onto a striker which hits the primer and the charge output pressure vs. time characteristic was measured (measurement range was from atmospheric pressure to 39.6 MPa); 20 runs were performed per sample.
Sensitivity of primers: Sensitivity of primers to impact was measured using the same apparatus that was used for performance measuring of the priming mixture. Primers were initiated by the fall of a 112 g ball onto a striker with primer.