Barium manganate is an inorganic compound with the formula BaMnO4. It is a type of manganate in which the manganese is in a +6 oxidation state. It is used as an oxidant in organic chemistry. It is made by heating manganese dioxide with barium carbonate or nitrate, or by precipitating potassium manganate with barium chloride.
Barium manganate produces a green pigment that was used to create manganese blue. It is a manganate, which means that the manganese is in an oxidation state of +6. Manganate should not be confused with permanganate, which also contains manganese (VII). Barium manganate is a powerful oxidant that is widely used in organic synthesis and can be used in a wide range of oxidation reactions.
Properties
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 MnO42- is longer than in MnO4– of 1.56 Å and shorter than the Mn-O bond found in MnO2, 1.89 Å. Barium manganate is isomorphous with BaCrO4 and BaSO4. Barium manganate can appear as a dark blue or green to black crystals. Barium manganate is indefinitely stable, active and can be stored for months in dry conditions.
- Chemical formula: BaMnO4
- Molar mass: 256.26 g/mol
- Appearance: light blue to dark blue and black powder
- Density: 4.85 g/cm3
- Solubility in water: insoluble
Preparation
Barium manganate can be prepared from potassium manganate and barium chloride by salt metathesis to give insoluble barium manganate:
BaCl2 + K2MnO4 → 2 KCl + BaMnO4↓
Applications
Barium manganate can be used to efficiently and selectively oxidize a wide range of functional groups, including alcohols to carbonyls, alcohols to aldehydes, diols to lactones, thiols to disulfides, aromatic amines to azo-compounds, hydroquinone to p-benzoquinone, benzylamine to benzaldehyde, and others.
Another use for barium manganate was as a pigment for making the artist’s color manganese blue. It is no longer used for that purpose; instead, paint manufacturers substitute a synthetic manganese blue hue.
Uses in organic synthesis
Barium manganate efficiently and selectively oxidizes a variety of functional groups, including 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, and others. Saturated hydrocarbons, alkenes, unsaturated ketones, and tertiary amines are not oxidized. MnO2 is frequently substituted with barium manganate. It is simpler to prepare, more efficient in reaction, and the substrate:oxidant ratios are closer to theory.
