Catalytic synthesis of humic acids from phenolic compounds by Mn(IV) oxide (Birnessite)

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Abstract
Extract Humic acids are natural organic polymers and are important constituents of soils (Kononova 1966). Although the mechanisms of the formation of humic acids are very complicated, the oxidative polymerization of polyphenols is considered to be one of the most important mechanisms (Kononova 1966; Stevenson 1982). The oxidative polymerization can be accelerated by enzymes (e.g., Haider et al. 1975; Flaig et al. 1975) as well as by inorganic components (e.g., Kyuma and Kawaguchi 1964; Shindo and Huang 1982; Kumada 1987). Shindo and Huang (1985) and Shindo and Higashi (1986) compared the relative effectiveness of several oxides, primary minerals, and clay minerals in promoting the synthesis of humic polymers from hydroquinone, and found that the promoting effect of Mn(IV) oxide was most striking among the inorganic components studied. The catalytic power of inorganic components in the synthesis of humic polymers from phenolic compounds may be influenced by the chemical structure of the compounds. However, little information is available on this aspect.