STUDIES OF THE THERMAL BEHAVIOR OF SOME POLYNUCLEAR AROMATICS

Abstract

Recent investigations of the pyrolysis of some polynuclear aromatic hydrocarbons have provided an insight into the carbonization mechanisms. Studies of the thermal behavior of a variety of such compounds have been conducted for the purpose of further elucidating these mechanisms, particularly the precarbonization reactions. A combination of differential thermal analysis, chromatographic, and spectrophotometric techniques has proved a valuable approach to this problem. Differential thermal analysis permits the categorization of these hydrocarbons as either chemically reactive or unreactive to thermal treatment at atmospheric pressure. The hydrocarbons, anthracene, pyrene, phenanthrene, and fluorene, are representative of the unreactive class which undergo mere melting and distillation at atmospheric pressure. Examples of the reactive category are dianthranyl, acenaphthylene, decacylene, naphthacene, pentacene, and bifluorylidene, all of which undergo exothermic polymerization prior to distillation. This molecular growth provides the necessary physical stability to permit further thermal reaction without volatilization. The application of chromatographic and spectrophotometric techniques to products obtained at reaction temperatures of these aromatics has demonstrated the importance of thermal hydrogen transfer reactions between aromatic hydrocarbon molecules. Such results, in addition to those reported by other workers, indicate that internal hydrogen transfer is an important process in the carbonization sequence.