OCCURRENCE AND GEOCHEMICAL SIGNIFICANCE OF 1,2,5,6-TETRAMETHYLNAPHTHALENE

Abstract

Analysis of aromatic hydrocarbon fractions of selected coal and shale samples reveals the predominance of two specific polyalkylnaphthalenes which have been identified as 1,2,5-trimethylnaphthalene and 1,2,5,6-tetramethylnaphthalene. The maturity of the samples is such that the source effect on the formation of individual molecules from biological precursors is expected to be recognisable. These alkylnaphthalenes are thought to be diagenetically derived from pentacyclic triterpenoids via 8,14-seco-triterpenoids, which are also detectable in some of the samples investigated. It is proposed that 1,2,5,6-tetramethylnaphthalene, in the coal samples, is formed by cleavage and methyl shift reactions from geminal C-4-methylated triterpenoids which contain a leaving group in position 3. For the shale samples, degradation of monoaromatic secohopanoids must be considered as an alternative pathway.