Four solid-crystal forms of paraazoxyanisole and the thermodynamic relationships between them

It is shown that paraazoxyanisole has four solid-crystal forms. The heats and temperatures of melting and transition are related by the following five equations: Q _m(IV) = Q _m(II); Q _m(IV) = Q _m(I) + Q _m(III); T _m(IV) = T _m(III); T _tr(II–III) = T _m(I); and Q _tr(II–III) = Q _m(I), Q _m(SCIV) = 52.0 ± 0.3 kJ/mol. Earlier, similar relationships were established for the third homologue of paraazoxyanisole, Q _mSCIV(C₃)] = 48.2 kJ/mol. It is found that for paraazoxyphenetole, Q _mSCIV(C₂)] = 46.0 kJ/mol.