Evolution of CO2 during birnessite-induced oxidation of C-14-labeled catechol

Phenolic compounds undergo several transformation processes in soil and wat er (i.e., partial degradation, mineralization, and polymerization), many of which have been attributed primarily to biological activity. Results from previous work indicate that naturally occurring Mn oxides are also capable of oxidizing phenolic compounds. In the present study, C-14-labeled catecho l was reacted with birnessite (manganese oxide) in aqueous suspension at pH 4. The mass of catechol-derived C in solid, solution, and gas phases was q uantified as a function of time. Between 5 and 16% of the total catechol C was liberated as CO2 from oxidation and abiotic ring cleavage under various conditions. Most of the C-14 (55-83%) was incorporated into the solid phas e in the form of stable organic reaction products whereas solution phase C- 14 concentrations increased from 16 to 39% with a doubling of total catecho l added. Polymerization and CO2 evolution appear to be competitive pathways in the transformation of catechol since their relative importance was stro ngly dependent on initial birnessite-catechol reaction conditions. Solid ph ase Fourier transform infrared (FTIR) spectra are consistent with the prese nce of phenolic, quinone, and aromatic ring cleavage products. Carbon dioxi de release appears to be limited by availability of reactive birnessite sur face sites and it is diminished in the presence of polymerized reaction pro ducts.