PHYSICOCHEMICAL AND STRUCTURAL RELATIONSHIPS OF ORGANIC CHEMICALS UNDERGOING SOIL- AND CLAY-CATALYZED FREE-RADICAL OXIDATION1

Abstract

This paper discusses soil- and clay-catalyzed oxidations in order to develop general guidelines for predicting the occurrence of these reactions. In this study, 93 organic chemicals that undergo soil- and clay-catalyzed oxidation were analyzed to identify similarities in (a) molecular structure and (b) physicochemical properties. Based on this analysis, we divided these chemicals into four groups: Group1—aromatic chemicals that contain electron-withdrawing and weak electron-donating fragments (they have a lower water solubility limit of 200 ppm); Group 2—aromatic chemicals that contain electron-withdrawing fragments and a very strong electron-donating fragment (lower water solubility limit is 112 ppm); Group 3—aromatic chemicals that contain only electron-donating fragments (lower water solubility limit is 29 ppm); and Group 4—aromatic chemicals that contain extensive conjugation (in general, these chemicals have a lower water solubility limit in the very low parts-per-million to high parts-per-billion range). We propose a hypothetical relationship between the lower solubility limit and chemical structure to chemical reactivity, using simple kinetic theory. Finally, we discuss the applicability of the solubility and structure characteristics of the four groups as guidelines for predicting the occurrence of free-radical oxidation.