Theoretical calculations by R. Bardo predict that under high pressure, p-Nitroaniline (PNA) forms semiconducting condensation products which possibly may be retained at ambient conditions. A combination phase-reaction P,T diagram has been determined in order to evaluate the correctness of the prediction and to indicate possible synthesis routes. The data were obtained by a combination of optical microscopy, x-ray diffraction, and Fourier transform infrared (FTIR) spectroscopy coupled with a diamond anvil high pressure cell. The results show, (1) a reversible crystallographic transition occurs at about 4.0 GPa; (2) a reversible transition at about 1.0 GPa and 140°C which effects the optical properties of the material also occurs; (3) the melting point increases to 245°C at 1.0 GPa; and (4) irreversible chemical reactions begin to be significant above 280°C and 1.0 GPa. The reaction products were investigated by mass spectrometry. A series of dimers with N or N-N linkages are formed under pressure at moderate temperatures. If temperatures at pressure are excessive, i. e., above 360°C, then the PNA reacts to form an amorphous material stable when heated to over 350°C.
G. J. Piermarini,
"The Pressure Synthesis Of P-Nitroaniline Condensation Products", Proc. SPIE 0878, Multifunctional Materials, (3 May 1988); doi: 10.1117/12.943951; https://doi.org/10.1117/12.943951