Pyrolysis of Acetylene behind Shock Waves

The pyrolysis of acetylene was investigated behind the reflected shock waves in a single-pulse shock tube over the temperature range from 1000 to 1670 K. The major products were 1-buten-3-yne, 1,3-butadiyne, and hydrogen. The main primary C4 product, however, changes from 1-buten-3-yne to 1,3-butadiyne with the increase of temperature. At the lower temperatures the formation of 1-buten-3-yne dominates the pyrolysis of acetylene. The rate of 1-buten-3-yne formation is second order with respect to acetylene concentration, and its second-order rate constant is expressed as follows: k(cm^3 mol^-1s^-1)=10^14.39±0.26exp((-46400±1400)/RT) The isotopic distribution of 1-buten-3-yne in the pyrolysis of the equimolar C2H2 and C2D2 mixture, proved that the pyrolysis proceeds via a free-radical mechanism. A free-radical chain mechanism initiated by the bimolecular reaction of acetylene, 2C2H2→C4H3+H, was proposed.