The Reaction of o‐Benzyne with Vinylacetylene: An Unexplored Way to Produce Naphthalene

• Published in: Chemphyschem Vol. 23; no. 2; pp. e202100758 - n/a
• Main Authors: Monluc, Lisa, Nikolayev, Anatoliy A., Medvedkov, Iakov A., Azyazov, Valeriy N., Morozov, Alexander N., Mebel, Alexander M.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 19.01.2022
• Subjects: Ab initio calculations; Chemical bonds; Exothermic reactions; Mathematical analysis; Naphthalene; ortho-benzyne; polycyclic aromatic hydrocarbons; Potential energy; potential energy surface; Radicals; rate constant; Rate constants; ortho-benzyne; Ab initio calculations; polycyclic aromatic hydrocarbons; rate constant; potential energy surface
• DOI: 10.1002/cphc.202100758
• ISSN: 1439-4235

The mechanism and kinetics of the reaction of ortho‐benzyne with vinylacetylene have been studied by ab initio and density functional CCSD(T)‐F12/cc‐pVTZ‐f12//B3LYP/6‐311G(d,p) calculations of the pertinent potential energy surface combined with Rice‐Ramsperger‐Kassel‐Marcus ‐ Master Equation calculations of reaction rate constants at various temperatures and pressures. Under prevailing combustion conditions, the reaction has been shown to predominantly proceed by the biradical acetylenic mechanism initiated by the addition of C4H4 to one of the C atoms of the triple bond in ortho‐benzyne by the acetylenic end, with a significant contribution of the concerted addition mechanism. Following the initial reaction steps, an extra six‐membered ring is produced and the rearrangement of H atoms in this new ring leads to the formation of naphthalene, which can further dissociate to 1‐ or 2‐naphthyl radicals. The o‐C6H4+C4H4 reaction is highly exothermic, by ∼143 kcal/mol to form naphthalene and by 31–32 kcal mol−1 to produce naphthyl radicals plus H, but features relatively high entrance barriers of 9–11 kcal mol−1. Although the reaction is rather slow, much slower than the reaction of phenyl radical with vinylacetylene, it forms naphthalene and 1‐ and 2‐naphthyl radicals directly, with their relative yields controlled by the temperature and pressure, and thus represents a viable source of the naphthalene core under conditions where ortho‐benzyne and vinylacetylene are available. New way to naphthalene: Electronic structure calculations of the potential energy surface for the reaction of ortho‐benzyne with vinylacetylene combined with RRKM‐ME calculations of reaction rate constants at various temperatures and pressures show that the reaction represents a viable source of the naphthalene core under conditions where the concentrations of o‐C6H4 and C4H4 are sufficient.