Structural transformations of polylabdanoid resinites during maturation

Three polylabdanoid resinites ranging in age from Eocene to Miocene were analyzed by pyrolysis-gas chromatography-mass spectrometry and solid-state nuclear magnetic resonance spectroscopy. The goal of the study was to determine effects on the chemical composition of polylabdanoid resinites following maturation processes. The samples studied included two Victorian Brown Coal resinites from the Yallourn and Morwell coal seams in Victoria, Australia, and a resinite from the Brunner coal measure in Nelson, New Zealand. Results of CPMAS 13C NMR experiments have determined a progressive decrease in total olefinic carbon content (per diterpenoid) with increasing maturity. Olefin reduction occurs primarily via a diminution in exocyclic methylene carbons of the labdatriene precursors (i.e. communic acid, communol, and/or biformene and their analogs). Analysis of Soxhlet extracted samples by py-GC-MS has shown a transformation from pyrolysis products indicative of communic acid polymers (hydronaphthenic acids) to a pyrolyzate containing a significant proportion of alkyl(hydro)naphthalenes. Condensation of the resinite polymer occurring in conjunction with defunctionalization reactions has been proposed.