The pyrolysis of organic compounds under conditions of carbon formation

Abstract

Studies of the pyrolysis of furan, thiophene, pyrrole and cyclopentadiene at ca. 1000°C have involved analysis of the gaseous products and determination of the structure and properties of the resulting surface carbons. The principal hydrocarbon products formed from each ring compound are methane and benzene, which appear to be stable, and acetylene and ethylene, which are reactive intermediates. When the starting compound contains a hetero-element, this is almost completely absent from the deposited carbon and appears in the gaseous products as water, hydrogen sulphide or hydrogen cyanide. Nitric oxide, when added in sufficient quantities, inhibits the formation of all gaseous products. The nature of the decomposition products, together with thermochemical considerations, support the conclusion that the ring compounds decompose by similar mechanisms and that the hydrocarbon fragments involved in carbon formation are essentially the same. The observed differences in the properties of the carbons are best explained in terms of the scavenging action of free radicals derived from the heterocyclic compounds. It appears that these radicals, which are formed at an early stage of decomposition, tend to remove blocking groups from crystallite edges and thereby promote crosslinking between the carbon crystallites.