The Study of Mg(II) Ion Influence on Catechol Autoxidation in Weakly Alkaline Aqueous Solution

High performance liquid chromatography with diode array detection (HPLC-DAD) and electron spin resonance (ESR) spectroscopy were used to study Mg(II) ion influence on the autoxidation of catechol in weakly alkaline solution. The presence of Mg(II) ions greatly enhanced the catechol autoxidation rate and probably influenced the mechanism of reaction thus enabling formation of reaction products not obtained in the absence of metal ions. Consecutive formation of 1,2-benzoquinone, 2,3-oxanthrenediol, and 2,3-oxanthrenedione with intermediate o-semiquinone anion radicals during the initial stages of catechol autoxidation was suggested based on the detailed analysis of experimental HPLC-DAD and ESR data. The results of this study may help in better understanding of autoxidation of some biologically important catecholic molecules in real systems, where Mg(II) ions are ubiquitously present. Because of the possible toxicity of simple quinone molecules, it is important that the formation of relatively stable quinoid autoxidation products were detected in this study.