Thermal Decomposition of 2‑Cyclopentenone

The thermal decomposition\nof 2-cyclopentenone, a cyclic oxygenated\nhydrocarbon that occurs in the pyrolysis of biomass, has been studied\nin a combined experimental and theoretical approach. Gas-phase pyrolysis\nwas performed at temperatures ranging from 1000 to 1400 K in a pulsed,\nmicrotubular reactor. Products were identified by FTIR spectroscopy\nfollowing their isolation in a low-temperature argon matrix. The following\nproducts were identified: carbon monoxide, ketene, propenylketene,\nvinylacetylene, ethylene, propene, acrolein, acetylene, propyne, and\npropargyl radical. Computational results identify three different\ndecomposition channels involving a H atom migration, and producing\nprop-2-enylketene (Pathway 1), prop-1-enylketene (Pathway 2), and\na second conformation of prop-2-enylketene (Pathway 3). A fourth decomposition\npathway involves simultaneous rupture of two C–C bonds forming\na high energy cyclopropenone intermediate that further reacts to form\nethylene, acetylene, and carbon monoxide. Finally, a fifth pathway\nto the formation of acrolein and acetylene was identified that proceeds\nvia a multistep mechanism, and an interconversion from 2-cyclopentenone\nto 3-cyclopentenone was identified computationally, but not observed\nexperimentally.