Thermal Conversion of Pregeijerene into Geijerene in Essential Oil of <i>Chromolaena Odorata</i> L. King & Robinson (Asteraceae)

It is well-known that geijerene is mostly associated with pregeijerene. These terpenes are believed to be thermoconvertible by a type of sigmatropic transposition order supra or antarafaciale. Our contribution to the study of the molecular pair consisted on a combination of statistical and analytical approach to the chemical composition of <i>Chromolaena odorata</i> essential oil. A compilation of chemical compositions of the samples obtained by steam distillation and analyzed by GC, presented a variation of this binomial proportions in different countries. For Ivory Coast, the results of analysis of 71 samples showed a dominance of geijerene proportion. We carried out a two-stage sampling by chemical variability factors (effects of site and period). We chose, at random, three different samples we submitted separately to chromatographic analysis (GC) and spectroscopic analysis (13C-NMR). It appears from this study that pregeijerene and geijerene were found in the essential oil with a relationship characterized by a polynomial degree 6 between these both molecules. Then during the chromatographic analysis, thermal conversion of pregeijerene into geijerene with the ratio 85.8% was observed. This result supported the idea of the coexistence of pregeijerene and geijerene in the essential oil of <i>Chromolaena</i> <i>odorata</i>. We intend to help clarify the kinetics and complete thermodynamics of this equilibrium.