Ring-opening pathway of 2, 4, 6-trichlorophenol initiated by OH radical: an insight from first principle study

Ring-opening studies of Chlorophenols (CPs) are an important issue to recognise the various end degradation products which may affect the environment and human health. Therefore, here we have explored the ring-opening pathway of 2, 4, 6-trichlorophenol (2, 4, 6-TCP) initiated by OH radical using quantum chemical investigations. Electronic structures and frequencies of all species of the titled reaction are obtained from the density functional theory method using M06-2X functional along with a 6-311++G(d,p) basis set. We have further performed energetic calculations of all optimised species using the CCSD(T) coupled-cluster method combined with the same basis set to achieve more accurate energy values. The full degradation pathway of 2, 4, 6-TCP + ^•OH reaction is shown by potential energy diagram at 298 K and 1 atm. The values of standard enthalpy change (Δ_rH⁰) and Gibbs free energy change (Δ_rG⁰) of all the reaction steps involved in the ring-opening pathway are also reported herein. From the energy calculations, we found that chloroethyne (HC≡CCl), carbon dioxide (CO₂) and C(Cl)O^• radical are the end degradation products in the ring-opening pathway.