Theoretical study on the formation mechanisms, dynamics and the effective catalysis of the nitrophenols

Abstract

AbstractThe hydrogen abstraction reactions of mono‐substituted phenols and nitrogen dioxide may be the sources of HONO and phenoxy radical. Further addition reaction of NO2 and phenoxy radical can form 2‐nitrophenol (2‐NP) and 4‐nitrophenol (4‐NP). The specific formation mechanisms and dynamics of NPs have drawn significant attention in recent days. The promoted reaction mechanisms by water, phenol and intermediate have also been studied. Compared with the naked reaction, the catalytic pathways can reduce the energy barrier from 48.40 kcal/mol to 18.23, 23.03 and 18.87 kcal/mol to form 2‐NP, respectively. Water molecules are the most effective catalysts, and the energy barrier could be further reduced to 8.20 kcal/mol when three water molecules are participating in the reaction. Water molecules can not only promote the formation of 4‐NP, but also simplify the reaction steps. In general, the water molecules serve as catalysts in the formation of NPs. The rate constants of 2‐NP and its hydrates have been predicted. The results are listed as follows: k2‐NP =3.82×10−13; k2‐NP‐1W =2.43×10−7; k2‐NP‐2W =3.39×10−4 cm3molecule−1s−1. The rate constants of mono‐substituted phenols (methylamino phenol, aminophenol and hydroquinone) and NO2 are also predicted by the traditional transitional state theory and variational transition state theory using the B3LYP/6‐311++G(3df,3pd)//6‐311++G(d). For the most dominant path, the rate constants for o/m/p‐methylaminophenol are 1.91×10−14, 4.28×10−20 and 8.78×10−15 cm3molecule−1s−1, respectively.