Pericyclic Pathways in the Mechanism of Coal Liquefaction

Abstract

At typical coal liquefaction conditions, namely temperatures from 300 to 400/sup 0/C and reaction times on the order of 1 hr, hydrogen transfer from model C10 donors, the ..delta../sup 1 -/ and ..delta../sup 2/-dialins, to model C14 acceptors, anthracene and phenanthrene, occurs in the sense allowed by the Woodward--Hoffman rules for supra-supra group transfer reactions. Thus, in the conversion of the C14 substrates to their 9,10 dihydro derivatives the dialins exhibited a striking reversal of donor activity, the ..delta../sup 1/-dialin causing about twice as much conversion of phenanthrene but only one-tenth as much conversion of anthracene as did ..delta../sup 2/-dialin. The dialins were also found to be more effective donor solvents than tetralin in the liquefaction of an Illinois No. 6 HVA bituminous coal. For example, at 400/sup 0/C and 0.5 hr reaction time, ..delta../sup 2/-dialin yielded 16% more pyridine-solubles and 37% more hexane-solubles than tetralin; at 300/sup 0/C and 0.5 hr reaction time, the ..delta../sup 2/-dialin yielded 5 times the pyridine-solubles and 3 times the benzene-solubles yielded by tetralin. Finally, a mixture containing equal parts of ..delta../sup 1/- and ..delta../sup 2/-dialin was found to be a more effective donor solvent than either of the ..delta../sup 1/- or ..delta../sup 2/-dialinsmore » separately. At 400/sup 0/C and 0.5 hr reaction time, the mixture of donors yielded 18% more pyridine-solubles and 28% more hexane-solubles than the average for the separate donors. The preceding experiments offer preliminary support to our notion that pericyclic pathways might be intimately involved in the mechanism of coal liquefaction. More specifically, the results indicate that pericyclic group transfer reactions constitute a plausible pathway for the transfer of hydrogen from donor solvents to coal during liquefaction. 2 figures, 4 tables.« less