Hydrogen exchange in some coal-related reactions at 400/sup 0/C

Data are available for kinetics of the transfer of hydrogen from tetralin and other hydrogen-rich solvents, but not much is known about the detailed mechanism involving individual linkages or groups in coal. In order to obtain some of this information, we have chosen to work with the pure compounds, 1,2-diphenylethane (bibenzyl), and diphenylmethane as models for certain linkages in coal. Because the thermolysis of the compound gives some different products when heated alone or when heated in the presence of a good hydrogen donor, such as tetralin, it was of interest to know where the cleavage fragments derive their hydrogen to give the final product. While the source of hydrogen needed to cap off the thermolysis fragments is obvious when bibenzyl is heated alone, its origin is ambiguous when tetralin is present. In order to resolve this aspect of the reaction, we prepared bibenzyl completely deuterated (99.8%) in the dimethylene linkage, and pyrolyzed it in the presence of ordinary tetralin. The products were isolated and their hydrogen and deuterium content were determined. From the data we conclude that the benzyl radical, formed by cleavage of bibenzyl, gives toluene by abstracting hydrogen from tetralin. The product after 1 percent conversion wasmore » PhCD/sub 2/H. Further, it was observed that, upon heating the mixture for eight hours, deuterium appeared in all the compounds. A considerable amount of deuterium exchange had taken place. In fact, in this mixture, tetralin-bibenzyl-d/sub 4/ at 400/sup 0/C, deuterium is lost from bibenzyl by exchange 3 to 4 times faster than it undergoes carbon-carbon bond scission. Thus, the chemistry of bibenzyl at 400/sup 0/ is dominated by hydrogen exchange reactions.« less