Ring cleavage and oxidative transformation of pyrogallol catalyzed by Mn, Fe, Al, and Si oxides

The nature of oxide in soil and associated environments in influencing the abiotic transformations of polyphenols still remains to be established. The objective of this study was to investigate the catalytic power of Mn(IV), Fe(III), Al, and Si oxides in the abiotic ring cleavage of pyrogallol and the polycondensation of the resulting fragments in air and N-2 atmosphere. The catalytic power varied greatly with the nature of the oxides. The synergistic effects of oxygen molecules and oxides also played an important role in affecting the transformations of pyrogallol, The results indicate that the release of CO2 as a result of ring cleavage of pyrogallol enhanced the development of carboxylic group contents of humic polymers formed in the reaction systems. The abiotic ring cleavage of polyphenols catalyzed by soil inorganic components such as short-range ordered oxides of Al and especially Fe and Mn may account, in part, for the carboxylic group contents and the origin of the aliphaticity of humic substances in soils.