Kinetic investigation of some steroids by thermogravimetry

The kinetic values of thermal degradation of some steroids were calculated by using TG and DTG curves and the Freeman-Carroll and the Jeres methods. Then andE _a values calculated by the Jeres method are more reasonable. The kinetic thermal stabilities of the simple functional groups of the steroids were compared by using theE _a values of Jeres, and the following sequences were found: 17β-OH>17-octy 1>17-Ac-CHO>17-keto; 3β-OH> 3-keto>3a-OH; and 5a-H>5β-H>Δ⁵⁽⁶⁾>Δ⁴. The k,Z, ΔH^*, ΔS^* and ΔG^* values were calculated at the maximum decomposition rate temperatures by using the Jeres values. The ΔS^* values are negative and suggest a high ordering of the transition state. The ΔH^* and ΔG^* values are positive, as expected.