THERMOCHEMICAL DECOMPOSITION OF CHOLIC-ACID AND ITS DERIVATIVES

The thermal decomposition reactions of cholic acid (1), methyl cholate (2), 3 alpha-acetoxy-7 alpha,12 alpha-dihydroxy-5 beta-methylcholanate (3), 3 alpha,7 alpha-diacetoxy-12 alpha-hydroxy-5 beta-methylcholanate (4), 3 alpha,7 alpha-diacetoxy-12 alpha-oxo-5 beta-methylcholanate (5) and 3 alpha,7 alpha,12 alpha-triacetoxy-5 beta-methylcholanate (6) were studied by DTA and TGA. The thermal decomposition of cholic acid proceeds as a one stage process in the range 200-420 degrees C. The esterification of the carboxylic group of cholic acid results in considerable increase of the thermal stability of compound (2). The endothermic peaks at about 100 degrees C occurring only in compounds (1) and (2) can be attributed to desolvation and release of hygroscopically bound water. The thermal decomposition reactions of the dried compound (2) and compounds (3), (4) and (5) are found to proceed in two stages. During the first stage, the thermal degradation of (5) leads to the formation of a completely deacetylated compound and two monodeacetylated compounds with the predominant product resulting from the elimination of the acetate group at C-3. Degradation of the carbon skeleton takes place during the second stage.