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Benzyl azide was investigated by high-pressure Raman scattering spectroscopy and X-ray diffraction technologies. A complete vibrational analysis of benzyl azide was performed by combining the experimental measurements and theoretical calculations using DFT-based scaled quantum chemical approach. The high-pressure Raman spectra and calculation results indicate that benzyl azide underwent a conformational change at 0.67 GPa accompanied by rotation of methylene group and azide group. The frequency of the CH2 bending mode decreases with increasing pressure due to the increase of the C-H···π interactions, which is similar to the role of the hydrogen bond. A liquid to solid phase transition occurred at 2.7 GPa, which was confirmed by the X-ray diffraction measurements. As the pressure reached 25.6 GPa, all the azide group vibrations vanished, indicating that the decomposition pressure of the molecular azide groups in organic azides is lower than that of the azide ions in inorganic azides.

The effect of high pressure on the phase transition behaviors of 4-toluenesulfonyl azide (C7H7N3O2S, 4-TsN3) have been investigated by Raman scattering and angle-dispersive X-ray diffraction (ADXRD) measurements in diamond anvil cells up to ∼15.6 GPa at room temperature. The liquid 4-TsN3 (phase I) begins to transform into solid state (phase II) at 0.7 GPa, and turns to phase III at about 2.7 GPa, then going to phase IV at about 6.3 GPa. The phase IV of 4-TsN3 finally starts to turn into an amorphous state above 10.6 GPa. The first phase transition (phase I to phase II) of 4-TsN3 is triggered by the rearrangement of CH···π interaction, and the second phase transition (phase II to phase III) is attributed to the conformational change, then the rotation of sulfonyl leads to the third phase transition (phase III to phase IV). The variation of sulfonyl has an influence on the behavior of azide group which will bend and further decompose upon compression. In the process of amorphization, the lattice structure of 4-TsN3 abnormally expanded, which may be caused by the change of CH···π interactions. We anticipate that the high pressure study of 4-TsN3 provides information toward further understanding and optimizing synthesis conditions of the polymeric nitrogen using azides as starting materials, especially using organic azides.

The azide group becomes increasingly asymmetric with increasing pressure, and the amorphization pressure of azide group is much lower than that of inorganic azide.

We have reported the high-pressure behavior of 4-acetamidobenzenesulfonyl azide (CHNOS, 4-ABSA) by in situ Raman scattering, IR absorption, and synchrotron angle-dispersive X-ray diffraction (ADXRD) measurements in diamond anvil cells with the pressure up to ∼13 GPa at room temperature. All of the fundamental vibrational modes of 4-ABSA at ambient pressure were analyzed by combination of experimental measurements and theoretical calculations using the density functional theory method. Detailed Raman and IR spectroscopic analyses reveal two phase transitions in the pressure region of 0.8-2 and 4.2 GPa, respectively, which are confirmed by the changes in the ADXRD patterns. The first phase transition in the pressure region of 0.8-2 GPa is attributed to the ring distortion and the rotation of CH group, whereas the second phase transition at 4.2 GPa might be induced by the rearrangement of azide group and hydrogen bonds. The analyses of the N vibrational modes suggest that the bent azide group rotates progressively upon compression, which is ascribed to the compression of the unit cell along the b axis. This study is helpful to understand the behavior of azide group and structural evolution of 4-ABSA under high pressure.