Synthesis and Properties of Long Chains of sp‐Hybridized Carbon Atoms: Polyynes

Abstract

Polyynes, a class of molecules described by the general formula H‐(C≡C)mH (where m is an integer) can be synthesized using an electric arc between graphite electrodes submerged in an organic solvent such as methanol, n‐hexane, n‐dodecane, decalin, or acetonitrile. The longest polyyne chain has been obtained when the electric arc is struck in acetonitrile at −40°C; polyyne chains up to 18 carbon atoms (m=9) have been produced together with monocyanopolyyne series as by‐products. When the arc between graphite electrodes is struck in liquid nitrogen, a mixture of dicyanopolyynes are obtained. The most recent development results on the rationalization of the mechanism of formation of polyynes from the submerged arc with new and noteworthy results are reviewed. The chemistry and the photochemistry of the polyynes solution are discussed including the reduction of polyynes to ene‐ynes. The application of polyynes range from astrochemistry to biochemistry. For instance cyanopolyynes are present in circumstellar media; polyynes are involved as intermediates in the formation of fullerenes, PAHs (polycyclic aromatic hydrocarbons), and soot. Polyynes are also biologically active molecules having antibiotic and antitumoral properties.