Polyynes production in a solvent-submerged electric Arc between graphite electrodes - II. Analysis by liquid chromatography

The electric arc between two graphite electrodes submerged in a solvent like acetonitrile produces a complete homologous series of polyynes having the general formula H(Cequivalent toC)(m)H (with m an integer: 1, 2, 3, 4, 5, 6, 7, 8,...). Analysis of the crude reaction mixture with liquid chromatography (HPLC) using a C-8 column and a diode-array detector (DAD) permits to separate all the molecular species of the mentioned homologue series and to identify each component on the basis of the peculiar electronic absorption spectrum. It is shown that all polyynes with m > 2 to m = 8 are produced in the arc, accumulated in the solvent and separated by HPLC and identified unequivocally by DAD. Thus, polyyne carbon chain having 16 carbon atoms has been produced easily at room temperature with the submerged electric arc technique. The hydrogen-capped polyynes are the main products but also polyyne chains with adventitious end groups have been identified by the HPLC analysis. The fact that the polyynes produced are essentially hydrogen-terminated as per the requirement of the general formula, was also demonstrated on the basis of their reactivity with a specific reagent for terminal acetylenic groups and also on the basis of the detection of the H(Cequivalent toC)(m)H groups by FF-IR spectroscopy.