Polymorphs of 2,4,5,6-tetrachloro-1,3-benzenedicarbonitile and their transformations

Kinetic Study for Comprehensive Understanding of Solid-State Polymorphic Transitions of Nicotinamide/Pimelic Acid Cocrystals

“…Calculated values were 3–5 times higher than the enthalpy measured during heating of form 1 (Δ sub H m = 104.0 ± 15.1 kJ mol –1 ) obtained by TGA analysis (see Supporting Information, Figure S5). The large variation between these values was previously reported in other kinetic studies, ,,− but the relation between E a and the enthalpy measured with the TGA remains unclear. Mnyukh suggested that molecular rearrangement (phase propagation) occurs at the solid–solid interface in the existence of effective gap by “stimulated sublimation” after nucleation of a new phase is formed .…”

Polymorphic Phase Transition in 4′-Hydroxyacetophenone: Equilibrium Temperature, Kinetic Barrier, and the Relative Stability of Z′ = 1 and Z′ = 2 Forms

“…A survey of reported activation energies for solid–solid phase transitions and sublimation enthalpies of the compounds involved in the processes shows that E a values considerably higher than Δ sub H m ° are not uncommon. Thus, in the case of 1,1-diamino-2,2-dinitroethylene (FOX-7), while the estimated enthalpies of sublimation for an unspecified polymorph lie in the range Δ sub H m ° = 109–116 kJ·mol –1 , , the experimentally obtained activation energies of the β → γ and γ → δ transitions are E a (β → γ) = 215 kJ mol –1 and E a (γ → δ) = 647 kJ mol –1 , respectively; for 2,4,5,6-tetrachlorobenzene-1,3-dicarbonitrile (chlorothalonil), Δ sub H m ° = 107 kJ·mol –1 and E a (α → β) = 650 kJ mol –1 ; for 2-(2,3-dimethylphenyl)­aminobenzoic acid (form I), Δ sub H m °(cr I) = 133 kJ·mol –1 and E a (I → II) = 300–362 kJ mol –1 ; − and in the case of the widely studied octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) system, Δ sub H m ° = 162 kJ·mol –1 and E a (β → δ) = 204–510 kJ·mol –1 . − The significance of these large activation energies (larger than the sublimation enthalpies) is impossible to assess without detailed information about the phase transition mechanism, which in the above examples, as in the case of HAP, is essentially unknown. The HAP results suggest, nevertheless, a complex nucleation and growth process consisting of several elementary steps characterized by their own individual E a that add up to a large overall value (also dubbed apparent activation energy).…”

Polymorphism and Solvatomorphism 2005

“…Differential scanning calorimetry was used to study the phase interconversion associated with the α and β polymorphs of 2,4,5,6‐tetrachloro‐l,3‐benzenedicarbonitile (chlorothalonil) 148. It was reported that the transition point for the α → β transition was 150.5 ± 0.1°C, and that the phase transition was characterized by an enthalpy of 4.03 ± 0.03 kJ/mol and an activation energy of 650 ± 90 kJ/mol.…”