Barium manganate is an inorganic compound with the formula BaMnO4. It is used as an oxidant in organic chemistry.[1] It belongs to a class of compounds known as manganates in which the manganese resides in a +6 oxidation state. Manganate should not be confused with permanganate which contains manganese(VII). Barium manganate is a powerful oxidant, popular in organic synthesis and can be used in a wide variety of oxidation reactions.
The manganate(VI) ion is a d1 ion and is tetrahedral with bond angles of approximately 109.5°. The Mn−O bond lengths in BaMnO4 and K2MnO4 are identical at 1.66 Å. In comparison, the Mn-O bond length in is longer than in MnO4− of 1.56 Å and shorter than the Mn−O bond found in MnO2, 1.89 Å.[2] [3] Barium manganate is isomorphous with BaCrO4 and BaSO4. Barium manganate can appear as a dark blue or green to black crystals.[4] Barium manganate is indefinitely stable, active and can be stored for months in dry conditions.[4]
Barium manganate can be prepared from potassium manganate and barium chloride by salt metathesis to give insoluble barium manganate:[5]
Barium manganate oxidizes a number of functional groups efficiently and selectively: alcohols to carbonyls, diols to lactones, thiols to disulfides, aromatic amines to azo-compounds, hydroquinone to p-benzoquinone, benzylamine to benzaldehyde, hydrazones to diazo compounds, etc.[6] It does not oxidize saturated hydrocarbons, alkenes, unsaturated ketones, and tertiary amines. Barium manganate is a common substitute for MnO2. It is easier to prepare, reacts more efficiently, and the substrate:oxidant ratios are closer to theory.
Another use for barium manganate was as a reagent in the synthesis of the inorganic pigment manganese blue, which is no longer produced on an industrial scale.