Reduction and dissolution of manganese(III) and manganese(IV) oxides by organics: 2. Survey of the reactivity of organics

Reduction and dissolution of manganese(III, IV) oxide suspensions by 27 aromatic and nonaromatic compounds resembling natural organics were examined in order to understand the solubilization reaction in nature. At pH 7.2, 10⁻³ M formate, fumarate, glycerol, lactate, malonate, phthalate, propanol, propionaldehyde, propionate, and sorbitol did not dissolve appreciable amounts of oxide after 3 h of reaction. The following organics did dissolve manganese oxides under these conditions and are listed in order of decreasing reactivity: 3-methoxycatechol ~ catechol 3,4-dihydroxybenzoic acid ~ ascorbate > 4-nitrocatechol > thiosalicylate > hydroquinone > 2,5-dihydroxybenzoic acid > syringic acid > o-methoxyphenol > vanillic acid > orcinol - 3,5-dihydroxybenzoic acid > resorcinol > oxalate ~ pyruvate - salicylate. Relative reactivities of organic substrates are discussed in terms of surface complex formation prior to electron transfer. Dissolution of manganese oxides by marine fulvic acid was enhanced by illumination, verifying that the reaction is photocatalyzed.