Crystal and pVT data and thermodynamics of the phase transitions of 2-methyl-2-nitropropane

Abstract

The lattice symmetry and lattice parameters of the low-temperature solid forms I1 and I of 2-methyl-2-nitropropane (TBN), (CH,),CNO,, have been determined by X-ray powder diffraction and found to be of the orthorhombic and face-centred cubic type, respectively. The pVT data have been determined in the temperature range 228 to 353 K up to ca. 300 MPa, as well as the volume changes accompanying the phase transitions. The volume changes allow the calculation, via the Clausius-Clapeyron equation of the corresponding entropy changes. The volume changes on melting decrease markedly with increasing pressure, whereas those at the solid-solid transitions (I1 -, I and 111 + 11) exhibit a much less pronounced pressure dependence. With regard to the entropy changes, only the I1 -+ I transition shows a small dependence (decrease) on increasing pressure. The two mean parts of the entropy changes (configurational and volume-dependent terms) are discussed for each transition.

The Pressure-Temperature Phase Diagram of Metacetamol and Its Comparison to the Phase Diagram of Paracetamol

“…For α V,I , it leads to 2.50×10 -4 K -1 and for α V,II 1.98×10 -4 K -1 can be found. Both expansivity coefficients are close to the average value of about 2×10 -4 K -1 found for molecular solids [10][11][12][13][14][15][16][17][18][19] and active pharmaceutical ingredients. [20][21][22][23] However, a closer study of the two expressions 2 and 3 and the data in Table 1 demonstrates that although form I appears to be denser at low temperature, it exhibits the largest thermal expansion (α V,I > α V,II ) and at room temperature its density is actually less than that of form II.…”

The High-Pressure Effect on the Phase Transition in Pyridinium Hexafluorophosphate

“…In order to find out the exact number of the possible inequivalent positions of the ions, the value of the volume entropy is needed. One of the methods of its estimation is based on the following formula [11,12]:…”

Plastic crystal behaviour in tetraethylammonium dicyanamide

“…The volume change across the plastic transition in organic ionic plastic crystals has not been studied before, but has been studied in molecular plastic crystals using XRD [7,[29][30][31]. Plastic crystals were almost invariably found to change from various crystal structures to a cubic crystal structure with larger lattice parameters (e.g.…”

“…across the plastic transition [7,32]. Dilatometry over a range of pressures [9,[29][30][31]33], useful to gain PVT data, have also been used to examine the change in bulk volume of materials across the plastic transition confirming the expansion of the material at the transition. Studies have also been conducted on the formation of vacancies during a plastic transition for many materials [34][35][36][37], though these studies did not also observe the effect on the volume of the bulk materials.…”