Identification and comparison of low-molecular-weight neutral constituents in two different coal extracts

A two-step pyridine and then tetrahydrofuran solvent extraction procedure at room temperature under nitrogen gas flow was used to extract two different U.S. coals, PSOC-592 (Illinois No. 5) and PSOC-521 (Rock Springs No. 7, Wyoming). Aliphatic and aromatic hydrocarbons were separated using neutral alumina column chromatography. The aromatics were then fractionated according to the number of aromatic carbons by high performance liquid chromatography (h.p.l.c.). These neutral compounds were identified by gas chromatography (g.c.) and gas chromatography/mass spectrometry (g.c./m.s.). n-Alkanes (C17C31), pristane, phytane, hopanes (17αH, 21βH), and moretanes (17βH, 21αH) were found in aliphatic fractions of both coal extracts. Low-molecular-weight (2–4 rings) polycyclic aromatic hydrocarbons (PAH) were the major compounds in the aromatic fraction of the PSOC-592 coal extract. However, pentacyclic triterpenoid-like hydroaromatic hydrocarbons were the major components in the extract of the PSOC-521 coal. A number of new compounds were identified for the first time. Complementary structural information was obtained from 1H and 13C n.m.r. analysis of the isolated fractions.