A role of charge-transfer complex with iodine in the modification of coal tar pitch

Iodine introduced into coal tar pitch (CTP) can drastically alter its reolo gy and carbonization behavior. Here, the mechanism of interaction between i odine and CTP has been investigated by using various spectroscopic methods such as I-127-NMR, EPR and FT-IR. It is shown that some iodine molecules in filtrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spect roscopy (HYSCORE) revealed the molecular size of cation radicals, which con tain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine trea tment. These results strongly suggest that dehydrogenative polymerization o f CTP occurs during the iodine treatment. The cation radicals in the charge -transfer complexes accelerate the dehydrogenative polymerization and resul t in a high carbon yield. (C) 2000 Elsevier Science Ltd. All rights reserve d.