Novel Products from C₆H₅ + C₆H₆/C₆H₅ Reactions

Abstract

To date only one product, biphenyl, has been reported to be produced from C₆H₅ + C₆H₆/C₆H₅ reactions. In this study, we have investigated some unique products of C₆H₅ + C₆H₆/C₆H₅ reactions via both experimental observation and theoretical modeling. In the experimental study, gas-phase reaction products produced from the pyrolysis of selected aromatics and aromatic/acetylene mixtures were detected by an in situ technique, vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometry (TOFMS). The mass spectra revealed a remarkable correlation in mass peaks at <i>m</i>/<i>z</i> = 154 {C₁₂H₁₀ (biphenyl)} and <i>m</i>/<i>z</i> = 152 {C₁₂H₈ (?)}. It also demonstrated an unexpected correlation among the HACA (hydrogen abstraction and acetylene addition) products at <i>m</i>/<i>z</i> = 78, 102, 128, 152, and 176. The analysis of formation routes of products suggested the contribution of some other isomers in addition to a well-known candidate, acenaphthylene, in the mass peak at <i>m</i>/<i>z</i> = 152 (C₁₂H₈). Considering the difficulties of identifying the contributing isomers from an observed mass number peak, quantum chemical calculations for the above-mentioned reactions were performed. As a result, cyclopenta[<i>a</i>]indene, <i>as</i>-indacene, <i>s</i>-indacene, biphenylene, acenaphthylene, and naphthalene appeared as novel products, produced from the possible channels of C₆H₅ + C₆H₆/C₆H₅ reactions rather than from their previously reported formation pathways. The most notable point is the production of acenaphthylene and naphthalene from C₆H₅ + C₆H₆/C₆H₅ reactions via the PAC (phenyl addition–cyclization) mechanism because, until now, both of them have been thought to be formed via the HACA routes. In this way, this study has paved the way for exploring alternative paths for other inefficient HACA routes using the PAC mechanism.