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Synthesis of Copper aspirinate

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Uploaded on Dec 24, 2009

A simple experiment in transition metal complexes, copper aspirinate is formed by reacting acetylsalicylic acid with copper carbonate. Copper aspirinate is used to treat rheumatoid arthritis, and unlike copper (II) ions and aspirin alone, it avoids the toxicity of both.

Transition metal complexes are not ordinary ionic compounds, and do not necessarily seek a complete shell of valence electrons (18e- for the d block of elements). In this case, copper aspirinate does have 18 valence electrons, but there are many exceptions.

The electron configuration of copper aspirinate is predicted as follows:
Copper(0) - ground state - 11 electrons
Copper(II) - 2+ - 9 electrons
4 copper - alkoxy ligand bonds - 8 electrons
Copper - copper sigma bond - 1 electron

Thus, each copper atom has 9 + 8 + 1 electrons, for a total of 18.


The acetylsalicylate molecules are called ligands in transition metal complexes, and in this case are anionic ligands which formally create a sigma bond with the metal centre, and change the metal centre oxidation state.

Neutral ligands do contribute to the total electron count and share electrons with the metal centre, however they are only weakly bound, do not have a formal bond, and do not change the metal centre oxidation state.

Copper carbonate from copper sulfate:
- As an aside, you can make copper carbonate from the more common copper sulfate pentahydrate by this method:

- Dissolve 8.6g Na2CO3 in 40mL distilled water, and dissolve 20.2g CuSO4*5H2O in 73mL distilled water.
- Add the CuSO4 solution slowly to the sodium carbonate solution with stirring
- Filter by vacuum, wash with 100mL distilled water, then dry.
- Yield should be approximately 10g

See also:
http://en.wikipedia.org/wiki/Copper_a...
http://en.wikipedia.org/wiki/18-Elect...

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