Copper (II) acetate

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Copper (II) acetate
Chemical formula Cu(CH3COO)2
OTP appearance dark green crystals 
Molar Mass(g/mol) 181.63 
Boiling Point(°C) 240 
Density(g/cc) 1.882 
Solubility in water(g/L) 65.4 (0.36M) @20°C
97.5g (0.537M) @100°C 
Solubility in ethanol(g/L) 64.4 (0.35M)
NFPA 704
NFPA704.png
0
2
0
 

Uses

Other

  • organic oxidant
  • mordant
  • ceramic pigment
  • fungicide
  • accessible soluble copper (II) salt

Natural occurrence

  • Does not occur naturally.

Hazards

Character

Hydrates

  • Copper (II) acetate monohydrate has a molar mass of ~200. 0.36M (for 1L saturated solution) weighs ~71g.

Thermal decomposition

The thermal decomposition of CuAc2·H2O under 500 °C in air included three main steps.[1]

  1. Under 168°C the copper (II) acetate was dehydrated
  2. Between 168–302°C it began to decompose to volatile compounds, elemental copper, and mixed copper oxides
  3. Between 302–500 °C the decomposition completes leaving only copper (II) oxide

Production

Synthesis

Notes
  • The maximum molarity of copper acetate in water is 0.36Mol/L, and this is often a limiting factor in its production.
  • Vinegar (5%v/v, 0.874M, acetic acid) is above the (double) molarity which will dissolve the resultant product, so concentrated acetic acid is not necessarily worthwhile, and dilution (20% v/v water) (to 0.72M) may be worthwhile.
  • Air drying a solution of copper (II) acetate can result in some decomposition to copper oxide, so instead, use the preferred solvant, dry(er) ethanol. If a black precipitate forms, add distilled water or vinegar and warm with stirring until it dissolves once again.
Procedure
  1. Reflux/warm any of copper (II) oxide, copper carbonate, malachite or azurite with acetic acid or vinegar.
    CuO(s) + 2 CH3COOH(aq)
    {
    40-50°C}
    Cu(CH3COO)2(aq) + H2O
  2. Filter (or decant) the blue solution and retain residue (copper oxides) for next batch
  3. Extract crystals from concentrated solution
    1. Repeat
      1. Combine with 3 volumes of azeotropic ethanol
      2. Let stand and separate
      3. Pour off ethanol layer
      4. Evap, leaving crystals
      5. Return any condensed alcohol to azeotropic strength, and feed forward.
    2. Until source is clear

Testing

  • Characteristic (different colored) blue-green crystals and blue solutions.
  • Chemtest (acetate)

Purification

An unpublished paper[2] suggests:

  1. Dissolve 90g (~0.5mol) of copper (II) acetate in 1L boiling vinegar
  2. Chill to below 0°C
  3. Collect the crystals which form
  4. Wash them briefly with ice cold distilled water
  5. Wash in dry ethanol
  6. Wash in diethyl ether and/or hexane
  7. Dry using moderate heat (40°-50°C) and drying agents (e.g. calcium chloride), to avoid thermal decomposition to copper (I) acetate

Storage

Store as crystals, not as solution. Aqueous solution degrades (hydrolyzes?) giving a white precipitate which may be copper (I) acetate (Cu(CH3COO)) or basic copper acetate (Cu(OH)(CH3COO) + CH3COOH), or something entirely other.

Disposal

Thermal decomposition to insoluble mineral copper (II) oxide is simple. Mixing with sodium carbonate produces insoluble mineral copper carbonate and sodium acetate.

Vidnotes

  • Produce a saturated solution of copper acetate at 20C (65g(anh), 71.44g (hyd) per liter, ~0.36M) to show what the goal looks like
  • Show dilution of vinegar before reaction to get to 0.72M solution
  • Several days of boiling copper powder in diluted vinegar.
  • Show increasing boiling point as copper acetate concentration grows?
  • Pre-weigh 0.36M of copper powder
  • Cook copper on stove and measure weight before/after to get "degree" of oxidation.

See Also

References

  1. Lin,, Z.; Han, D.; Li, S (2012) "Study on thermal decomposition of copper(II) acetate monohydrate in air"
    Journal of Thermal Analysis Calorimitry 107; pp471. 
  2. Semenok, Dmitrii (2015) "Synthesis and purification of copper catalysts..."
    unpublished 
    DOI:10.13140/RG.2.1.2479.9204