Geosynthesis of organic compounds. Part V — methylation of alkylnaphthalenes

Several crude oils and rock extracts with high concentrations of 1,6-dimethylnaphthalene, 1,2,5-trimethylnaphthalene, 1,2,3,5-tetramethylnaphthalene, 1,2,3,5,6-pentamethylnaphthalene and 6-isopropyl-2-methyl-1-(4-methylpentyl)naphthalene are also shown to contain enhanced distributions of their corresponding methylated counterparts. Of these methylated counterparts, 1,2,3,5,6,7-hexamethylnaphthalene has been synthesised and is identified in sedimentary material for the first time. In laboratory experiments carried out under mild conditions with a methyl donor in the presence of a clay catalyst, each of the parent alkylnaphthalenes was shown to be substituted in preferential positions. The distributions of these products from laboratory methylation experiments are similar to the distributions found in sedimentary material. These observations have been interpreted as evidence for a sedimentary electrophilic aromatic methylation process.