Copper(II) Acetate

Copper(II) acetate

Copper(II) acetate
IUPAC name	Copper(II) acetate
Other names	Cupric acetate
Identifiers
CAS number	142-71-2 (anhydrous)6046-93-1 (monohydrate)
Properties
Molecular formula	Cu2(CH3COO)4
Molar mass	199.65 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 water20 g / mL hot waterSoluble in alcoholSlightly soluble in ether and glycerol
Structure
Crystal structure	Monoclinic
Hazards
MSDS	Baker MSDS
NFPA 704	010
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

Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu2(OAc)4 where AcO- is acetate (CH3CO2-). The hydrated derivative, which contains one molecule of water for each Cu atom, is 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 as a catalyst or an oxidizing agent in organic synthesis. Copper acetate, like all copper compounds, emits a blue-green glow in a flame.

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Contents 1 History 2 Uses in chemical synthesis 3 Structure 4 Synthesis 5 References

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.

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]

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 (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]

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

References

1. ^ P. Vogel, J. Srogl "Copper(II) Acetate" in "EROS Encyclopedia of Reagents for Organic Synthesis" Copper(II) Acetate, 2005 John Wiley & Sons.
2. ^ 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.
3. ^ Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press.
4. ^ R. L. Carlin "Magnetochemistry" Springer: Berlin, 1986
5. ^ S. J. Kirchner, Q. Fernando "Copper(I) Acetate" Inorganic Syntheses, 1980, volume XX, pages 53-55.
6. ^ Parish, E. J.; Kizito, S. A. "Copper(I) Acetate" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons. DOI: 10.1002/047084289X.rc193.

Categories: Copper compounds | Acetates | Oxidizing agents | Catalysts