Oxidations with Potassium trans-1,2-Diaminocyclohexanetetraacetatomanganate-(III). I. Composition of the Complex and the Reaction with Methanol

Abstract

The complex of manganese(III) with trans-1,2-diaminocyclohexanetetraacetic acid has been shown to exist as the crystalline monohydrate, KMnIIICyDTA(H2O), where CyDTA represents the ligand trans-1,2-diaminocyclohexanetetraacetate.In aqueous methanol (2.5% water v/v) three forms of the complex exist: MnIIICyDTA(H2O)− in neutral solution, MnIIICyDTA(OH)2− in base, and HMnCyDTA(H2O) in acid. In basic methanol the complex decomposes by disproportionation following first-order kinetics. When the same solvent system contains acid the disappearance of MnIII is first-order in complex and first-order in acid but in this case methanol is oxidized to formaldehyde.The isotope effects observed in the oxidation of CH3OD, CD3OH, and CD3OD are all small (1.25 or less). This together with the acid dependence indicates that the oxidation proceeds by rate-controlling electron abstraction from methanol by the protonated form of the complex, possibly via an intermediate in which one of the coordinating ligands is replaced by methanol.