Theoretical study of phenol and hydroxyl radical reaction mechanism in aqueous medium by the DFT/B3LYP/6-31+G(d,p)/CPCM model

Abstract

Four different possible reaction pathways of phenol and hydroxyl radical reaction were investigated theoretically by density functional theory (DFT) B3LYP with the 6-31+G(d,p) calculations under the conductor-like polarized continuum model (CPCM). According to frontier molecule orbital theory, both the highest occupied orbital and lowest occupied orbital of phenol (25th orbital) showed –602.79 and –43.53 kJ mol −1 molecular orbital energies, respectively. This resulted in a 559.27 kJ mol −1 relative energy gap. Relative energies of the ortho product radical (o-PR) (i.e., –54.08 kJ mol −1 ) was lower than those of both the para product radical (p-PR) (–50.03 kJ mol −1 ) and the meta product radical (m-PR) (–47.10 kJ mol −1 ). Then, o-PR was found to be the energetically most stable product radical. The ortho addition reaction path was confirmed as the most possible reaction path and its major intermediate was found as catechol with 99.09% product distribution. Percentages of hydroquinone, resorcinol, and phynoxyl radicals in the system were found as 0.053%, 0.029%, and 0.009%, respectively.