A DFT mechanistic and kinetic study on the reaction of phloroglucinol with (OH)-O-center dot in different media: Hydrogen atom transfer versus oxidation

A theoretical study on the reaction of phloroglucinol with (OH)-O-center dot has been performed with the aim of elucidating the geometric, energetic and kinetic properties of the reaction as well as identifying the preferred reaction pathway. Three reaction mechanisms have been considered, namely, direct hydrogen atom abstraction, addition-elimination mechanism in the absence and in the presence of a base catalyst and oxidation mechanism in the absence and in the presence of O-2. The study has been performed using the DFT/M06-2X, DFT/BHHLYP and DFT/MPW1K methods in conjunction with either the 6-31++G(d p) or the 6-311++G(3df,2p) basis set. The energetic parameters are influenced by the type of function utilized and the media in which the calculation is done. The direct hydrogen abstraction mechanism provides the smallest branching ratio with respect to the (OH)-O-center dot addition mechanisms. The PG + (OH)-O-center dot reaction under atmospheric conditions saturated with O-2 would predominantly form tetrahydroxybenzene; the predominant product within the biological system would largely depend on physiological conditions; under pH similar to 7 and with oxygen dissolved within the biological system, the preferred product would be tetrahydroxybenzene; however, if the reaction takes place in some part of the biological system where the pH > 7, the preferred product would be the phenoxyl radical.