Formation of phenanthrene via H‐assisted isomerization of 2‐ethynylbiphenyl produced in the reaction of phenyl with phenylacetylene

Abstract

AbstractModel chemistry G3(MP2,CC)//B3LYP/6‐311G(d,p) calculations of the potential energy surface for the reaction of phenyl radical (C6H5) with phenylacetylene (C8H6) have been carried out and combined with Rice‐Ramsperger‐Kassel‐Marcus/Master Equation calculations of temperature‐ and pressure‐dependent rate constants. The results showed that the reaction can serve as a viable source for the formation of phenanthrene via an indirect route involving a primary reaction of phenyl addition to the ortho carbon in the ring of phenylacetylene and H elimination producing 2‐ethynylbiphenyl followed by secondary H‐assisted isomerization of 2‐ethynylbiphenyl to phenanthrene. In the secondary reaction, the H atom adds to the α carbon of the ethynyl side chain, then a six‐member ring closure takes place followed by aromatization via an H loss. The channel of H addition to the side chain of 2‐ethynylbiphenyl appears to be much faster than H addition to the ortho carbon in the ethynyl‐substituted ring leading back to the initial C6H5 + C8H6 reactants. Rate constants for the primary C6H5 + C8H62‐ethynylbiphenyl (p1) + H and secondary p1 + Hphenanthrene (p2) + H reactions have been computed in the temperature range of 500‐2500 K at pressures of 30 Torr, 1, 10, and 100 atm and fitted to modified Arrhenius expressions. The suggested kinetic scheme and rate constants are proposed as a prototype for the modeling of the growth of polycyclic aromatic hydrocarbons via the phenyl addition‐dehydrocyclization (PAC) mechanism involving an addition of a PAH radical to an ethynyl‐substituted PAH molecule.