OXIDATION AND DECARBOXYLATION - A REACTION SEQUENCE FOR THE STUDY OF AROMATIC STRUCTURAL ELEMENTS IN POCAHONTAS NO.-3 COAL

Oxygen in basic solution has been used to oxidize Pocahontas No. 3 coa l to a mixture of aromatic carboxylic acids, and copper(I) oxide in N- methylpyrrolidinone-quinoline has been used to decarboxylate the acids to provide a mixture of hydrocarbons. Most pendant alkyl groups have been removed in this sequence and the product distribution is much les s complex than the product distributions that are obtained in direct o xidation reactions or in the analysis of coal liquids and extracts. Ap proximately 25% of the aromatic carbon atoms are retained in the produ cts. The structures of these compounds have been investigated by gas c hromatography-mass spectrometry and by high-resolution and laser desor ption mass spectrometry. Approximately 150 compounds were detected in the GCMS experiments including a broad array of bi-, ter-, and quatera ryls, fluorene and fluoranthene derivatives, polycyclic aromatic hydro carbons with four, five, and six rings, dibenzo-and dinaphthofurans, a nd dibenzo- and dinaphthothiophenes. High-resolution mass spectrometry provided additional evidence concerning the principal products and ex tended the mass range to approximately 400 Da. Laser desorption work r evealed that even larger molecules were present in the reaction produc ts with distinct signals at 550 Da and definite intensity extending to 1200 Da. These results are compatible with many other results that ha ve been obtained in the past decade and strongly infer that the relati vely high-ranking Pocahontas No. 3 coal has many large, condensed, aro matic clusters that are methylated and connected through biaryl and he terocyclic linkages.