Determination of the Apparent Reaction Rate Constants for Ozone Degradation of Substituted Phenols and QSPR/QSAR Analysis

Abstract

Although extensive experimental work has been carried out during the last several years, experimental reaction rate constants are available only for hundreds of compounds. Therefore, it is useful to develop a theoretical prediction method, which can be used to obtain estimates of the necessary kinetic parameters. One of the most successful approaches to predict chemical properties starting only from molecu- lar structural information is quantitative structure-activity/property relationships modeling (QSAR/QSPR). The purpose of this paper is to study the relationships between concentrations of 26 substituted phenols and reaction times during the ozonation process and determine the reaction orders and apparent reaction rate constants (-lgk´). Then, optimized geometries of the substituted phenols were carried out at the B3LYP/6- 311G** level using the Gaussian 03 software package. The structural and thermodynamic parameters ob- tained were taken as theoretical descriptors to establish a novel QSPR/QSAR model for -lgkof the substi- tuted phenols, with a regression coefficient R = 0.909 and standard deviation SD = 0.141. Finally, the stability of the model for -lgkpredictions was checked by the t-test, showing satisfactory results. Results obtained reveal the reliability of QSPR/QSAR model for the prediction of ozone degradations rate constant of organic compounds. Key word: Ozonation, Degradation rate, Density functional theory (DFT), Multiple linear regressions, Structural and thermodynamic parameters, E LUMO