REACTIONS OF PITTSBURGH NO.8 COAL WITH MALEIC-ANHYDRIDE - EVIDENCE FOR THE EXISTENCE OF REACTIVE DIENE STRUCTURES IN COAL

The reaction between C-13-labeled maleic anhydride and Pittsburgh No. 8 coal has been investigated by NMR. The occurrence of the following r eactions has been ruled out: ene reaction, maleic anhydride polymeriza tion, ester formation, radical addition, electron transfer, and physic al entrapment. Michael addition to -SH has been demonstrated in model systems, but does not occur with -OH groups and cannot explain the obs erved 10-20% (wt) incorporation of maleic anhydride. All data are cons istent with the occurrence of Diels-Alder reactions. There are not eno ugh reactive dienes in any coal structure model to yield the large mal eic anhydride incorporations observed. Either current coal structures are seriously incorrect or this coal is exhibiting strongly enhanced r eactivity whose origin is not understood.