Raman spectroscopic investigation of phase changes and reactivity of 1-pentadecene under high-pressure and high-temperature conditions

The phase changes and reactivity of 1-pentadecene (C₁₅H₃₀) were investigated using Raman spectroscopy under high-pressure and high-temperature conditions using diamond anvil cells. At room temperature, the phase changes from liquid phase to solid phase I, and solid phase I to solid phase II were observed at 0.3 GPa and 4.1 GPa, respectively. Another phase change to form phase III progressed at approximately 10 GPa, and a partial irreversible chemical reaction was observed after decompression from 15.7 GPa. Under high-pressure and high-temperature conditions, the irreversible chemical reaction extensively progressed from the solid phase at 180°C, 1.8 GPa, and at 210 °C, 5.4 GPa. The selective reduction of the Raman peak intensities corresponding to sp² carbon indicated the progression of an addition reaction similar to that observed in the 1-hexene reaction. A new CC stretching mode appeared, which was attributed to the non-terminal CC bond and was more evident at higher pressures. As the chemical reaction progressed from the liquid phase, a gradual reduction of the CC stretching mode peak was observed upon increasing the temperature at approximately 1.0 GPa, indicating the occurrence of a partial chemical reaction.