Abstract: This paper presents the study on thermodynamic characteristics of phase transitions for tanshinone Ⅱ-A, tanshinone Ⅱ-B and saprorthoquinone (hereafter abbreviated to 1,2 and 3 respectively) by Differential Scanning Calorimetry (DSC). The relationships of their molecular structures with thermodynamic parameters were discussed. The experimental results obtained are listed in Table 2.
The differences of nominated compounds for their melting points, melting enthalpies and melting entropies are as follows:
T_m~1>T_m~3, ΔH_m~1>ΔH_m~3, ΔS_m~1=ΔS_m~3;
T_m~1>T_m~2, ΔH_m~1>ΔH_m~2, ΔS_m~1=ΔS_m~2.

Key words: o-quinonoid form materials, Differential Scanning Calorimetry, Thermodynamics of drug