Copper(II) acetate
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| Copper(II) acetate | |
|---|---|
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| Systematic name | Copper(II) acetate |
| Other names | Cupric acetate |
| Molecular formula | Cu2(CH3COO)4 |
| Molar mass | 181.59 g/mol |
| Appearance | Dark green crystaline solid |
| CAS number | 142-71-2 (anhydrous) 6046-93-1 (dihydrate) |
| Properties | |
| Melting point | 115 °C (388 K) |
| Boiling point | 240 °C (513 K) |
| Solubility | 7.2 g/100 mL cold water 20 g / mL hot water Soluble in alcohol Slightly soluble in ether and glycerol |
| Density | 1.88 g/100 mL |
| Crystal structure | Monoclinic |
| Hazards | |
| MSDS | Baker MSDS |
| Hazard Codes | Xn, N |
| NFPA 704 |
0
1
0
|
| Flash point | Non-flammable |
| R/S statement | R: 22-36/37/38-50/53 S: 26-60-61 |
Copper(II) acetate, also referred to as cupric acetate, is Cu2(OAc)4 where -OAc is acetate or CH3CO2-. The hydrated version also contains two water molecules and is the form most commonly available commercially. Cu2(OAc)4 is a dark green crystalline solid, whereas Cu2(OAc)4(H2O)2 is more bluish-green. Since ancient times, copper acetates of some form have been used as fungicides and green pigments. Today, Cu2(OAc)4 is used as a source of copper(II) in inorganic synthesis and, in organic synthesis, as a catalyst or an oxidizing agent.
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[edit] History
Copper(II) acetate is speculated to be a component of verdigris, the blue-green substance that forms on copper during long exposures to atmosphere. It was historically prepared in vineyards, since acetic acid is a byproduct of fermentation. Copper sheets were alternately layered with fermented grape skins and dregs left over from wine production and exposed to air. This would leave a blue substance on the outside of the sheet. This was then scraped off and dissolved in water. The resulting solid was used as a pigment, or combined with arsenic trioxide to form copper acetoarsenite, a powerful insecticide and fungicide called Paris or Schwienfurt green.
[edit] Uses in chemical synthesis
The uses for copper(II) acetate are more plentiful as a catalyst or oxidizing agent in organic syntheses. For example, Cu2(OAc)4 is used to couple two terminal alkynes to make a 1,3-diyne:[1]
- Cu2(OAc)4 + 2 RC≡CH → 2 CuOAc + RC≡C-C≡CR + 2 HOAc
The reaction proceeds via the intermediacy of copper(I) acetylides, which are then oxidized by the copper(II) acetate, releasing the acetylide radical. A related reaction involving copper acetylides is the synthesis of ynamines, terminal alkynes with amine groups using Cu2(OAc)4.[2]
[edit] Structure
Cu2(OAc)4(H2O)2 adopts the "Chinese lantern" structure seen also for related Rh(II) and Cr(II) tetraacetates.[2][3] One oxygen atom on each acetate is bound to one copper at 1.97 Å. Completing the coordination sphere are two water ligands, with Cu-O distances of 2.20 Å. The two five-coordinate copper atoms are separated by only 2.65 Å, which is close to the Cu--Cu separation in metallic copper.[5]. The two copper centers interact resulting in a diminishing of the magnetic moment such that near 90K, Cu2(OAc)4(H2O)2 is essentially diamagnetic due to cancellation of the two opposing spins. Cu2(OAc)4(H2O)2 was a critical step in the development of modern theories for antiferromagnetic coupling.[4]
[edit] Synthesis
Copper(II) acetate has been synthesized for centuries by the method described in the history section. This method, however, leads to a fairly impure mixture of copper(II) acetate and the other components of verdigris. In a laboratory, a much purer form can be synthesized in a simple three-step procedure. The overall reaction is as follows:[6]
- CuSO4 + 4 NH3 + 4 CH3COOH → Cu2(OAc)4(H2O)2 + (NH4)2SO4
(note that CuSO4, "copper sulfate" is also typically hydrated).
The hydrate form can be dehydrated by heating at 100 °C in a vacuum:[5]
- Cu2(OAc)4(H2O)2 → Cu2(OAc)4 + 2 H2O
Heating a mixture of anhydrous Cu2(OAc)4 and copper metal affords colorless, volatile cuprous acetate:
- 2 Cu + Cu2(OAc)4 → 4 Cu2(OAc)2 + 4 HOAc
[edit] References
- ^ P. Vogel, J. Srogl "Copper(II) Acetate" in "EROS Encyclopedia of Reagents for Organic Synthesis" Copper(II) Acetate, 2005 John Wiley & Sons.
- ^ van Niekerk, J. N. Schoening, F. R. L. “X-Ray Evidence for Metal-to-Metal Bonds in Cupric and Chromous Acetate” Nature 1953, volume 171, pages 36-37. doi:10.1038/171036a0.
- ^ Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press.
- ^ R. L. Carlin "Magnetochemistry" Springer: Berlin, 1986
- ^ S. J. Kirchner, Q. Fernando "Copper(I) Acetate" Inorganic Syntheses, 1980, volume XX, pages 53-55.
[edit] External links
- Copper.org – Other Copper Compounds 5 Feb. 2006
- Infoplease.com -- Paris green 6 Feb. 2006
- Verdigris – History and Synthesis 6 Feb. 2006
- J.T. Baker MSDS – Cupric acetate
- National Pollutant Inventory - Copper and compounds fact sheet
- National Safety Council Chemical Backgrounder
- Sigma Aldrich Product Detail
