Copper(II) acetate
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| Copper(II) acetate | |
|---|---|
-acetate.jpg/200px-Copper(II)-acetate.jpg) |
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| IUPAC name | Copper(II) acetate |
| Other names | Cupric acetate |
| Identifiers | |
| CAS number | 142-71-2 (anhydrous) 6046-93-1 (monohydrate) |
| Properties | |
| Molecular formula | Cu(CH3COO)2 |
| Molar mass | 182 g/mol |
| Appearance | Dark green crystalline solid |
| Density | 1.88 g/mL |
| Melting point |
115 °C (388 K) |
| Boiling point |
240 °C (513 K) |
| Solubility in other solvents | 7.2 g/100 mL cold water 20 g / mL hot water Soluble in alcohol Slightly soluble in ether and glycerol |
| Structure | |
| Crystal structure | Monoclinic |
| Hazards | |
| MSDS | Baker MSDS |
| NFPA 704 |
 0
2
0
|
| R-phrases | 22-36/37/38-50/53 |
| S-phrases | 26-60-61 |
| Flash point | Non-flammable |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO- is acetate (CH3CO2-). The hydrated derivative, which contains one molecule of water for each Cu atom, is available commercially. Cu(OAc)2 is a dark green crystalline solid, whereas Cu(OAc)2(H2O)2 is more bluish-green. Since ancient times, copper acetates of some form have been used as fungicides and green pigments. Today, Cu(OAc)2 is used as a source of copper(II) in inorganic synthesis and as a catalyst or an oxidizing agent in organic synthesis. Copper acetate, like all copper compounds, emits a blue-green glow in a flame.
Contents |
[edit] History
Copper(II) acetate is the primary component of verdigris,[citation needed] 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 Schweinfurt green.
Copper (cupric) acetate tablets were believed to repel sharks in the mid twentieth century. SCUBA divers strapped tablets of the compound to their belt and/or ankles to provide protection against sharks. It was used by Jacques-Yves Cousteau and his researchers with questionable results1.
1 Cousteau, Jacques-Yves; Frédéric Dumas (1953). The Silent World. Harper and Row, Publishers, Inc., pp. 127-135. ISBN 0-7922-6796-6.
[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
-acetate-3D-balls.png/200px-Copper(II)-acetate-3D-balls.png)
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 (197 pm. Completing the coordination sphere are two water ligands, with Cu-O distances of 2.20 Å (220 pm). The two five-coordinate copper atoms are separated by only 2.65 Å (265 pm), 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 90 K, 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 an impure copper(II) acetate. In a laboratory, a much purer form can be synthesized in a simple three-step procedure. The overall reaction is as follows:[6]
- 2 CuSO4.5H2O + 4 NH3 + 4 CH3COOH → Cu2(OAc)4(H2O)2 + 2 [NH4]2[SO4] + 8 H2O
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:[6]
- 2 Cu + Cu2(OAc)4 → 4 CuOAc
[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.
- ^ Parish, E. J.; Kizito, S. A. "Copper(I) Acetate" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons. DOI: 10.1002/047084289X.rc193.
