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 (T(fusI) = 400.5 +/- 1.0 K, Delta(fus)H(I) = 36.6 +/- 0.9 kJ mol(-1)) recrystallizes into another phase, Phase II, that melts at T(fusII) = 373.8 +/- 0.2 K (Delta(fus)H(II) = 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.