QSARS FOR OXIDATION OF PHENOLS IN THE AQUEOUS ENVIRONMENT, SUITABLE FOR RISK ASSESSMENT

To assess the contribution of oxidation to the overall degradation of compounds in the environment, it would be helpful to have QSAR models which cover a large range of chemicals and/or degradation processes. A t present QSAR models for oxidation in the aqueous environment mainly deal with phenols and are restricted to a specific reaction with one o xidant present in the aqueous environment. In this paper we have gathe red data on oxidation of phenols with various aqueous phase oxidants t o compare the different processes. It is shown that existing models fo r oxidation can be extended by using the energy of the highest occupie d molecular orbital calculated with semiempirical molecular orbital me thods as a descriptor. The results from correlating reaction rate cons tants with this theoretical descriptor are equal to results using expe rimentally measured half-wave potentials. By using PLS analysis on tho se compounds having multiple response data, a single model comprising all oxidation rate constants with different oxidants is created. This analysis shows that for four out of five oxidants the electronic prope rties of the compound determine the reaction rate constants. These oxi dants are thought to react by the same mechanism, namely outer-sphere one-electron oxidation. The fifth oxidant, potassium dichromate, shows a different dependence on the descriptor variables, indicating a diff erent reaction mechanism.