Experimental and Computational Investigation of Benzofuran Decomposition Kinetics

Benzofuran (C₈H₆O) is a common oxygenated polycyclic aromatic hydrocarbon (OPAH) intermediate observed in the combustion of transportation and biofuels. It also serves as a crucial precursor in the formation of polycyclic aromatic hydrocarbons (PAHs) during the combustion process. This study investigated the decomposition kinetics of benzofuran by combining experimental and computational approaches. A chemical microreactor coupled with synchrotron vacuum ultraviolet photoionization mass spectrometry was employed to identify primary intermediates and products. The results revealed that fulvenallene is a major primary intermediate, while 2-ethynylphenol emerged as a unique isomeric product of benzofuran decomposition. Other significant intermediates identified include benzyl, fulvenallenyl, phenylacetylene, and benzyne. To elucidate the reaction pathways leading to these intermediates, potential energy surfaces (PESs) for unimolecular and H-addition bimolecular decomposition pathways were computed using the CCSD(T)(BD(T))/cc-pVTZ//B3LYP/6-311G(d,p) level of theory (for species with higher T1, the BD(T) method has been used). Although unimolecular decomposition pathways to fulvenallene and benzyne were identified, the associated energy barriers were considerably higher compared to the bimolecular pathways. The study identified fulvenallene as the primary ring-opening product on the C₈H₆O+H PES, formed predominantly through two pathways. Additionally, phenylacetylene, benzyne, and benzyl were shown to derive from this PES. Rate constants for the H-addition reactions were calculated to determine branching ratios among competing pathways. Furthermore, this study demonstrated that the primary monoaromatic intermediates, along with abundantly produced unsaturated alkyne/alkynyl radicals, act as precursors for the formation of higher (C₉H₈-C₁₄H₈) PAHs observed in this work.