Polymorphism in 2,4,6-trinitrotoluene

Topological pressure-temperature state diagram of the crystalline dimorphism of 2,4,6-trinitrotoluene

“…Then with the melting points found just above, one finds for the transition point 330.9 K, which confirms the transition temperature observed by Golovina of 328 K [8]. Thus, as is clear from the literature, the orthorhombic form can either transform to the monoclinic one through a solid-to-solid endothermic transition, melt, or melt and convert into the monoclinic form on heating as illustrated in Figure S1 in the supplementary materials [19]. Similar thermal behavior has been observed previously with piracetam phase III that either transforms to phase I or melts without transformation depending on the presence of traces of residual solvent [33,35].…”

“…Figure S1. Differential thermal analysis curves for TNT reported by Connick et al [19]. It was observed that monoclinic single crystals recrystallized from toluene solutions exhibited a single melting peak (peak 'b', panel a).…”

“…In this respect, it is clear that the melting point of form O cannot be positioned at a lower temperature than where the O®M transitions have been observed, otherwise O would have molten instead of transformed into M. It being clear from the literature that form M is the highest melting form, the melting equilibrium of form O must be found between the melting point of M and the observations of the O®M transition in the solid. This brings us to Figure S1 in the supplementary materials, which indicates that form O melts about one degree lower than form M [19]. Taking this temperature difference and applying that to the average melting temperature determined for form M of 352.9 ±1.3 K, form O would be expected to melt at 352 K. The melting points can be used to determine the solid-solid transition temperature using eq.…”

“…Simultaneously, Connick at al. carried out calorimetric and crystallographic studies that revealed two kinds of thermal behavior (see Figure S1 in the supplementary materials) [19]. Single-peak DTA curves with an onset at about 354 K were ascribed to the melting of the monoclinic polymorph by the authors who observed that 'single crystals grown from toluene solutions have a single peak melting endotherm and are monoclinic'.…”

“…By contrast, 'Double peaked endotherms are indicative of a mixture of the monoclinic and another polymorphic form, possibly orthorhombic. The proportion of each polymorph is variable and dependent on sample history' according to the authors [19]. The melting of the orthorhombic form occurred in these measurements between 353 and 353.5 K (See Table 2).…”