Computational Modeling of 2-Monochlorophenol and 2-Monochlorothiophenol

Abstract

Substituted phenolic compounds are well established organic contaminants in the atmosphere and natural ecosystems. They are implicated in a variety of health problems such as oxidative stress, cancer and respiratory diseases. Although the chemistry of 2-monochlorophenol is extensively studied experimentally, theoretical studies on this molecule especially on its thermal degradation is scarce in literature. The goal of this investigation is to investigate not only the thermal properties of 2-monochlorophenol and 2-monochrothiophenol but also their electronic properties from a theoretical stand point. To simulate the thermolysis of these pollutants under conditions representative of municipal waste incineration, a temperature range of 300-1000ËšC at typical increments of 100 ËšC at 1 atmosphere was chosen. Gaussian 03 computational suite of programs was employed in this study. The density functional theory (DFT) in conjunction with B3LYP correlation function and a variety of basis sets were used in this study. Two basis sets normally selected for molecular modeling of organic molecules; 6-31+G and 6-31G have been given priority in this work. Thermochemical results show that 2-mochlorothiophenol easily dissociates to 2-monochlorothiophenoxy radical in comparison to the dissociation of 2-monochlorophenol to 2-monochlorophenoxy radical in the whole range of degradation temperature. At a degradation temperature of 1000 K, the change in enthalpy for the formation of 2-monochlorothiophenoxy and 2-monochlorophenoxy radicals are respectively, 70.40 and 84.39 kcal mol^-1. The toxicities of these combustion by-products have also been reported in this study.