Synthesis of polyynes with electric arc - Part 5: Detection of PAHs as minor products

The main products of the submerged electric arc between graphite electrodes in n-hexane and in methanol are the polyynes series. The liquid chromatographic analysts (HPLC) of the arcing products in n-hexane reveals also the presence of a mixture of polycyclic aromatic hydrocarbons (PAHs) as minor products. Naphthalene. acenaphthylene, phenanthrene. perylene. fluoranthene. benz[b]fluoranthene, pyrene. and the related compound cyclopenta[c,d]pyrene have been identified. Even crysene and acenaphthene were reasonably identified from the PAHs mixture. The PAHs mixture appears to derive essentially from the plasmalysis of the solvent where the electric arc is conducted. while the polyynes are formed from the elemental carbon supplied from the graphite electrodes. Another minor product is represented in all cases by the formation of carbon black or carbon coke, which appears more abundant in n-hexane rather than in methanol. The different results are explained thermodynamically in terms of different carbonization tendency of the solvents used.