Molecular characterization of retene derivatives obtained by thermal treatment of abietane skeleton diterpenoids

Abstract

The thermal treatment of abietane skeleton diterpenoids yields a number of mono-, di- and tri-aromatic hydrocarbons. The aromatization process follows the thermal constraint and the degree of aromatization is higher with higher operating temperature. It seems possible to correlate the composition pitches with the thermal treatments specially those, which were used in Antic production sites. During the aromatization process, the retene, which is formed, is demethylated to give the 7-ethyl-1-methylphenanthrene and then the 1,7-dimethylphenanthrene. In the mean time, the retene is also methylated and gives methylretenes (MR) and dimethylretenes (DMR). The semi-empirical AM1/RHF method has been used to calculate local minimum structures of ∼60 retene-like molecules together with their relative enthalpies of formation. This study allows to correlate the calculated geometries and the stabilities and to link the thermodynamic properties and shapes of individual isomers with their relative abundance during thermal degradation.