THERMAL-ISOMERIZATION AND DECOMPOSITION OF 2-BUTYNE IN SHOCK-WAVES

The thermal isomerization and decomposition of 2-C4H6 behind reflected shock waves with 1100 < T5 < 1600 K and 1.6 X 10(-5) < rho5 < 2.1 x 1 0(-5) mol/cm3 were studied by UV kinetic absorption spectroscopy, IR l aser kinetic absorption spectroscopy, and gas-chromatographic analysis of reaction products. The major products of the pyrolysis were 1,2-bu tadiene, 1,3-butadiene, CH4, C2H2, C2H4, C2H6, allene, propyne, C4H2, vinylacetylene, and benzene. 1,3-Butadiene and 1,2-butadiene were prod uced before the appearance of any other decomposition products. This f act means that the very fast isomerizations of 2-butyne take place bef ore the decomposition. The present data were successfully modeled with a 80 reaction mechanism which included the isomerizations among 1- an d 2-butynes and 1,2- and 1,3-butadienes and the decompositions of thes e C4H6 isomers. From the modeling, the following rate constants of the isomerizations were obtained: 2-butyne = 1,3-butadiene (k = (3.0 X 10 (13)) exp(-65.0 kcal/RT) s-1), and 2-butyne = 1,2-butadiene (k = (3.0 X 10(13)) exp(-67.0 kcal/RT) s-1), where the activation energies, 65 a nd 67 kcal/mol, were estimated from literature data. We discussed the possible route of the isomerizations of 2-butyne to 1,3- and 1,2-butad ienes.