Description
Manganese (III) acetate is an inorganic compound that is used as an oxidizing agent in organic synthesis and materials science. Like the analogous acetates of iron and chromium, it is an oxygen-centered coordination complex containing three manganese atoms bridged by acetate units. The anhydrous form of this compound crystallizes as a linear coordination polymer, with an additional acetic acid molecule bridging between manganese atoms on consecutive three-manganese clusters.The chemical is therefore not a simple metal acetate ionic compound nor does the actual structure of it reflect the simple "Mn(OAc)
3" chemical formula that is commonly given. It is usually used as the dihydrate, though the anhydrous form is also used in some situations. The dihydrate is prepared by reacting potassium permanganate and manganese (II) acetate in acetic acid; addition of acetic anhydride to the reaction produces the anhydrous form.
Mangese triacetate has been used as a single electron oxidant. It can oxidize alkenes via addition of acetic acid to form lactones.
Chemical Properties
The cinnamon-brown crystals of a silky luster are immediately decomposed by cold water (hydration).
Uses
Mild and selective oxidizing agent. Catalyzes allylic oxidation of a variety of alkenes in the presence of
tert-butylhydroperoxide.
Reagent used for radical cyclizations and α-keto-acetoxylation.
Uses
Triacetoxymanganese Dihydrate functions as a catalyst for direct acetylation of alcohols with acetic acid.
Synthesis
In the method of Christensen, the salt is obtained in the following manner: 19.6 g. (80 mmoles) of Mn(CH3COO)3 -2H3O
powder is added to 200 ml. of glacial acetic acid at the boiling
temperature of the latter, and is stirred until completely dissolved. Then, KMnO4 powder (3.1 g. = 20 mmoles) is gradually
added and the mixture heated for a short time with constant
agitation. After cooling, 3 ml. of water is added to the darkbrown solution; the mixture is allowed to stand overnight. If the
quantity of precipitate is too small, another 3 ml. of water is
added and the solution stirred. The formation of crystallization
nuclei is promoted by frequent rubbing of the container walls
with a glass rod. As a rule, copious crystallization occurs within
about one hour. If necessary, the solution is allowed to stand for
a few more days (frequent agitation) until the mother liquor is
almost colorless. The salt is then filtered off with suction,
washed with some glacial acetic acid and recrystallized. The
last procedure consists in dissolving 30 g. of salt in 200 ml. of
glacial acetic acid (heating), filtering off and working up further
in the manner described above. Finally, the salt is dried over
CaO.
4 Mn(CH3COO)2 ? 4 H2O + KMnO4 + 8 CH3COOH = 5 Mn(CH3COO)3 ? 2 H2O + CH3COOK + 10 H2O
