Experimental observation of molecular-weight growth by the reactions of o-benzyne with benzyl radicals

Abstract

The chemistry of ortho-benzyne (o-C₆H₄) is of fundamental importance due to its role as an essential molecular building block in molecular-weight growth reactions. Here, we report on an experimental investigation of the reaction of o-C₆H₄ with benzyl (C₇H₇) radicals in a well-controlled flash pyrolysis experiment using a resistively heated SiC microtubular reactor at temperatures of 800–1600 K and pressures near 30  torr. To this end, the reactants o-C₆H₄ and C₇H₇ were pyrolytically generated from 1,2-diiodobenzene and benzyl bromide, respectively. Using molecular-beam time-of-flight mass spectrometry, we found that o-C₆H₄ associates with the benzyl to form C₁₃H₁₁ radicals, which decompose at higher temperatures via H-loss to form closed-shell C₁₃H₁₀ molecules. Our experimental results agree with earlier theoretical calculations by Matsugi and Miyoshi [Phys. Chem. Chem. Phys., 2012, 14, 9722–9728], who predicted the formation of fluorene (C₁₃H₁₀) + H to be the dominant reaction channel. At temperatures above 1400 K, we also observed the formation of C₁₃H₉ radicals, most likely the resonance-stabilized fluorenyl π-radical. Our study confirms that molecular-mass growth via the o-C₆H₄ + C₇H₇ reaction provides a versatile pathway for introducing five-membered rings, and hence curved structures, into polycyclic aromatic hydrocarbons.