Crystallization Thermodynamics And Thermal Decomposition Of Diosgenin

Diosgenin is an essential raw material for steroid hormone drugs and is also oneof important pharmaceutical precursors. Currently, diosgenin has attracted greatattention. However, more and more researchers are mainly interested in thetechnology of extraction and separation for diosgenin and ignore the fundamentalresearch of diosgenin. For lack of fundamental data for diosgenin, therefore, thisthesis focuses on three aspects of this basic research, such as (solid+liquid)equilibrium, crystal structure and thermal decomposition properties.Using synthetic method, solubilities of diosgenin in15different solvents aredetermined at different temperatures by a laser monitoring observation technique atatmospheric pressure. The solubility data were correlated with semiempiricalequations, such as the ideal model, λh model and Apelblat equation, which agreedwell with the experimental data and of which the AAD is lower than3%. Moreover,three activity coefficient models such as UNIQUAC model, NRTL model and Wilsonmodel are also used to correlate solubility of diosgenin. The results indicate thatUNIQUAC model is more accurate than NRTL and Wilson model with the AAD of4.68%. However, UNIQAUC model is failure to correlate the solubility of diosgeninin isobutyl alcohol and tert-butanol. But NRTL model has a good agreement with thesolubility in isobutyl alcohol and tert-butanol. Although AAD of NRTL model is littlehigher than that of UNIQUAC model, it also has an advantage on correlation ofsolubility in all solvents. Compared with NRTL model, Wilson model has the similaraccuracy. But the AAD of that is little higher. Additionally, the solubility of diosgeninin15solvents is also investigated at308.2K, the results of which indicates thatsolubility of diosgenin in n-alkanols tends to increase with increasing alkanol chainlength, iso-octyl alcohol (Particularly, this solvent is heterogeneous alcohols)>1-heptanol>1-hexanol>1-pentanol>1-butanol>1-propanol> ethanol> methanol.Solubility in n-alkanols is higher than that in heterogeneous alcohols for diosgenin,such as1-butanol> isobutyl alcohol> tert-butanol and1-propanol> isopropanol. For other solvents, there are in this order: Carbon tetrachloride> acetic ether> propylacetate> acetone. Overall, it turns out that solubility of diosgenin increased withsolvent polarity decreased.The crystallization of diosgenin was also investigated by programmed coolingmethod in this work. It can be found that the crystal structure of diosgenincrystallized in acetone is similar with that of experimental material. However, onesolvent compound of diosgenin can be obtained in methanol. Characterized by FTIR,DSC, and TG, it turns out that diosgenin and methanol are mixed in the crystal ofsolvent compound with3:1molecules form. Moreover, process of transformation wasinvestigated at25°C and55°C which indicates that it can be different crystalstructures of diosgenin under two different temperature conditions.In order to study the thermal stability of diosgenin, thermal decompositionproperties of diosgenin were studied by thermal gravimetric analysis. Possiblemechanism function of thermal decomposition and decomposition kinetics weredetermined for diosgenin. And thermodynamic parameters of thermal decompositionprocess were also calculated.(Solid+liquid) equilibrium, crystal structure and thermal decompositionproperties are investigated in detail, which will provide amount of valuable data tosupport for industrial design of diosgenin and further detailed theoretical studies.