New chemical structural features of coal. A comparison of several coals

Structural features of several coals of different ranks are compared using an adaptation of the transalkylation reaction. In the present application of this method, trifluoromethanesulphonic acid is used as catalyst and toluene is used in excess as acceptor and solvent. The process can be visualized as a disproportionation reaction in which intermolecular alkyl transfers occur. Under the influence of the acid catalyst, aryl-alkyl bonds in coal are cleaved and alkyl-aryl bonds are formed with the excess toluene solvent. Thus, a large number of substituted toluene derivatives are formed by transfer of groups from coal. Concentrations of ≈ 20 substituent groups and connecting groups are estimated and compared for a range of coals and numerous other compounds are present in small amounts. These compounds are tabulated for two coals and the possible significance and origin of some of them are discussed. The mechanism of the transalkylation reaction as it applies to coal and the reactions of a limited number of relevant model systems are also discussed.