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Manganese(III) acetate
Chemical compound

Manganese(III) acetate describes a family of materials with the approximate formula Mn(O2CCH3)3. These materials are brown solids that are soluble in acetic acid and water. They are used in organic synthesis as oxidizing agents.

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Structure

Although manganese(III) triacetate has not been reported, salts of basic manganese(III) acetate are well characterized. Basic manganese acetate adopts the structure reminiscent of those of basic chromium acetate and basic iron acetate. The formula is [Mn3O(O2CCH3)6Ln]X where L is a ligand and X is an anion. The salt [Mn3O(O2CCH3)6]O2CCH3.HO2CCH3 has been confirmed by X-ray crystallography.2

Preparation

It is usually used as the dihydrate, although the anhydrous form is also used in some situations. The dihydrate is prepared by combining potassium permanganate and manganese(II) acetate in acetic acid.3 Addition of acetic anhydride to the reaction produces the anhydrous form.45 It is also synthesized by electrochemical method starting from Mn(OAc)2.6

Use in organic synthesis

Manganese triacetate has been used as an oxidant in radical cyclizations. It can oxidize alkenes via addition of acetic acid to form lactones.7

This process is thought to proceed through rate determining enolization followed by intramolecular electron transfer to form [{Mn3}–enolate]• radical intermediates (e.g., [{Mn3}–enolate]), instead of free •CH2CO2H radical intermediates, which then react with the alkene, followed by additional oxidation steps and finally ring closure.89 When the alkene is not symmetric, the major product depends on the nature of the alkene, and is consistent with initial formation of the more stable radical (among the two carbons of the alkene) followed by ring closure onto the more stable conformation of the intermediate.10

When reacted with enones, the carbon on the other side of the carbonyl reacts rather than the alkene portion, leading to α'-acetoxy enones.11 In this process, the carbon next to the carbonyl is oxidized by the manganese, followed by transfer of acetate from the manganese to it.12 It can similarly oxidize β-ketoesters at the α carbon, and this intermediate can react with various other structures, including halides and alkenes (see: manganese-mediated coupling reactions). One extension of this idea is the cyclization of the ketoester portion of the molecule with an alkene elsewhere in the same structure.13

See also

References

  1. Snider, Barry B.; Meunier, Alexandre; Legaul, Claude Y. (2001). "Manganese(III) Acetate". Encyclopedia of Reagents for Organic Synthesis. Wiley. doi:10.1002/047084289X.rm018.pub2. ISBN 0-471-93623-5. 0-471-93623-5 ↩

  2. Hessel, L. W.; Romers, C. (1969). "The Crystal Structure of "Anhydrous Manganic Acetate"". Recueil des Travaux Chimiques des Pays-Bas. 88 (5): 545–552. doi:10.1002/recl.19690880505. /wiki/Doi_(identifier) ↩

  3. E. I. Heiba; R. M. Dessau; A. L. Williams; P. G. Rodewald (1983). "Substituted γ-butyrolactones From Carboxylic Acids And Olefins: γ-(n-octyl)-γ-butyrolactone". Org. Synth. 61: 22. doi:10.15227/orgsyn.061.0022. /wiki/Doi_(identifier) ↩

  4. Snider, Barry B.; Meunier, Alexandre; Legaul, Claude Y. (2001). "Manganese(III) Acetate". Encyclopedia of Reagents for Organic Synthesis. Wiley. doi:10.1002/047084289X.rm018.pub2. ISBN 0-471-93623-5. 0-471-93623-5 ↩

  5. Hessel, L. W.; Romers, C. (1969). "The Crystal Structure of "Anhydrous Manganic Acetate"". Recueil des Travaux Chimiques des Pays-Bas. 88 (5): 545–552. doi:10.1002/recl.19690880505. /wiki/Doi_(identifier) ↩

  6. Yılmaz, M.; Yılmaz, E. V. B.; Pekel, A. T. (2011). "Radical Cyclization of Fluorinated 1,3-Dicarbonyl Compounds with Dienes Using Manganese(III) Acetate and Synthesis of Fluoroacylated 4,5-Dihydrofurans". Helv. Chim. Acta. 94 (11): 2027–2038. doi:10.1002/hlca.201100105. /wiki/Doi_(identifier) ↩

  7. E. I. Heiba; R. M. Dessau; A. L. Williams; P. G. Rodewald (1983). "Substituted γ-butyrolactones From Carboxylic Acids And Olefins: γ-(n-octyl)-γ-butyrolactone". Org. Synth. 61: 22. doi:10.15227/orgsyn.061.0022. /wiki/Doi_(identifier) ↩

  8. Fristad, William E.; Peterson, John R.; Ernst, Andreas B.; Urbi, Gordon B. (1986-01-01). "Mechanisms for Manganese(III) Oxidations with Alkenes". Tetrahedron. 42 (13): 3429–3442. doi:10.1016/S0040-4020(01)87310-5. ISSN 0040-4020. https://linkinghub.elsevier.com/retrieve/pii/S0040402001873105 ↩

  9. Snider, Barry B. (2009-12-26). "Mechanisms of Mn(OAc)3-based oxidative free-radical additions and cyclizations". Tetrahedron. Electron Transfer Reagents in Organic Synthesis. 65 (52): 10738–10744. doi:10.1016/j.tet.2009.09.025. ISSN 0040-4020. PMC 2902773. PMID 20640037. https://linkinghub.elsevier.com/retrieve/pii/S0040402009013726 ↩

  10. Fristad, W. E.; Peterson, J. R. (1985). "Manganese(III)-mediated γ-lactone annulation". J. Org. Chem. 50 (1): 10–18. doi:10.1021/jo00201a003. /wiki/Doi_(identifier) ↩

  11. Dunlap, Norma K.; Sabol, Mark R.; Watt, David S. (1984). "Oxidation of enones to α'-acetoxyenones using manganese triacetate". Tetrahedron Letters. 25: 5839–5842. doi:10.1016/S0040-4039(01)81699-3. /wiki/Doi_(identifier) ↩

  12. Williams, G. J.; Hunter, N. R. (1976). "Situselective α'-acetoxylationof some α,β-enones by manganic acetate oxidation". Can. J. Chem. 54 (24): 3830–3832. doi:10.1139/v76-550. /wiki/Doi_(identifier) ↩

  13. Snider, B. B.; Patricia, J. J.; Kates, S. A. (1988). "Mechanism of manganese(III)-based oxidation of β-keto esters". J. Org. Chem. 53 (10): 2137–2141. doi:10.1021/jo00245a001. /wiki/Doi_(identifier) ↩