Formation
of Furan along with HO<sub>2</sub> during the OH-Initiated Oxidation
of 2,5-DHF and 2,3-DHF: An Experimental and Computational Study
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Abstract
Experimental characterization of
products during OH-initiated oxidation of dihydrofurans (DHF) confirms
the formation of furan accompanied by the formation of HO<sub>2</sub> to be a significant channel in 2,5-DHF (21 ± 3%), whereas it
is absent in 2,3-DHF. Theoretical investigations on the reaction of
OH with these molecules are carried out to understand this difference.
All possible channels of reaction are studied at M06-2X level with
6-311G* basis set, and the stationary points on the potential energy
surface are optimized. The overall rate coefficients calculated using
conventional TST with Wigner tunneling correction for 2,5-DHF and
2,3-DHF are 2.25 × 10<sup>–11</sup> and 4.13 × 10<sup>–10</sup> cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup>, respectively, in the same range as the previously
determined experimental values. The branching ratios of different
channels were estimated using the computed rate coefficients. The
abstraction of H atom, leading to dihydrofuranyl radical, is found
to be a significant probability, equally important as the addition
of OH to the double bond in the case of 2,5-DHF. However, this probability
is very small in the case of 2,3-DHF because the rate coefficient
of the addition reaction is more than 10 times that of the abstraction
reaction. This explains the conspicuous absence of furan among the
products of the reaction of OH with 2,3-DHF. The calculations also
indicate that the abstraction reaction, and hence furan formation,
may become significant for OH-initiated oxidation of 2,3-DHF at temperatures
relevant to combustion