ABSTRACT
Methanol: A Comparison with Carbon Arc . . . . . . . . . . . . 161 8.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
8.3.1 Some Kinetic Aspects on the Formation of Polyynes . . . . 161 8.3.2 Detection and Identification of Polyynes by
HPLC-DAD and Other Analytical Techniques . . . . . . . . . . 164 8.3.3 PAHs as Byproducts Formed with the Polyynes
During Arcing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 8.3.4 The Role Played by the Nature of the Electrodes in the
Polyynes Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 8.3.5 Formation of Carbon Coke or Pyrocarbon:
A Comparison with a Series of Halogenated Solvents. . . . 176 8.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
Polyynes are a fascinating class of molecules because they are involved in many processes and in many different fields of science. For instance, it has been demonstrated that they are the precursors in fullerene synthesis [1-7]. Since nanotubes and nanohorns are obtained under electric arc conditions similar to those adopted for polyyne production [8-11], it may be supposed that they may also play a role in nanotube formation. Furthermore, polyynes are also considered the key intermediates in the mechanism of soot formation in flames or in thermal decomposition processes of hydrocarbons [12]. Polyynes also represent a very wide class of naturally occurring organic molecules synthesized by plants, microorganisms, and fungi; about 1000 of naturally occurring polyynes are known [13]. They display biological activity, including antibiotic and anticancer activity [13] and may find application in the treatment of certain diseases. Carbon chains are also produced from carbon-rich late-type stars and are released in the interstellar medium. It is quite possible that in this medium the carbon chains are the precursors of several exotic molecules and also of interstellar carbon dust. Polyyne derivatives known as cyanopolyynes have been identified by radioastronomy in the molecular clouds of the interstellar medium [14]. It is quite astonishing that the largest molecule identified till now in molecular clouds of the interstellar space is just a cyanopolyyne: C11N. Polyynes are thought to also play a major role in the interstellar medium and have been advocated as a source of the diffuse interstellar bands (DIBs), although this has not been definitively proven [15-17], and they may play a role in the formation mechanism of interstellar carbon dust. Polyynes and cyanopolyynes are present in the atmosphere of Titan, the giant moon of Saturn, and are thought to be involved in the haze formation in this satellite [18-20]. Furthermore, the formation of polyynes and derivatives is expected also in the atmospheres of the giant gaseous planets such as Jupiter and Saturn and have been found in cometary dust [21]. Polyyne chains are also considered as models of molecular wires and in the synthesis of push-pull chemical structures [22].
