Overall Monotropic Behavior of a Metastable Phase of Biclotymol, 2,2′-Methylenebis(4-Chloro-3-Methyl-Isopropylphenol), Inferred From Experimental and Topological Construction of the Related P-T State Diagram

The melt from the usual monoclinic phase (Phase I) of biclotymol (TfusI = 400.5 ± 1.0 K, ΔfusHI = 36.6 ± 0.9 kJ mol−1) recrystallizes into another phase, Phase II, that melts at TfusII = 373.8 ± 0.2 K (ΔfusHII = 28.8 ± 1.0 kJ mol−1). The transformation of Phase II into Phase I is found to be exothermic upon heating either as a direct process at 363 K or through a melting-recrystallization process (II → liquid → I). The melting curves, obtained from differential thermal analyses at various pressures ranging from 0 to 85 MPa, diverge as the pressure increases ((dP/dT)fusI = 2.54 ± 0.07 MPa K−1, (dP/dT)fusII = 5.14 ± 0.85 MPa K−1). A topological P-T diagram with no stable phase region for Phase II, and similar to the 4th case of the P-T state diagrams formerly published by Bakhuis Roozeboom, is drawn, thus illustrating the overall monotropic behavior of Phase II.