How is Cr(acac)₃ synthesized?

I am trying to find the specific reaction pathways that urea, chromium (III) chloride hexahydrate and acetylacetone undergo to synthesize Cr(acac)3. I need this information to find the percent yield for a project I am doing.
Mandy Letchworth

Mandy,

You have to remove the (somewhat acidic) hydrogen on the central carbon in the acetylacetone before it will chelate to the chromium(III). I'm guessing that's what the urea is for. The urea reacts with water to yield CO₂, ammonium ion, and hydroxide ion. The hydroxide ion then reacts with the acetylacetone, abstracting the hydrogen on the central carbon, producing the acac- ion.

The reactions involved are

(H₂N)₂CO + 3 H₂O = CO₂ + 2 NH₄⁺ + 2OH^-
CH₃COCH₂COCH₃ + OH^- = acac- + H₂O
CrCl₃.6H₂O = Cr³⁺ + 3Cl^- + 6H₂O
Cr³⁺ + 3acac- = Cr(acac)₃ Now, to compute the percent yield,

1. Obtain a net equation for the synthesis by combining the equations above.
2. Find a yield for each of the starting materials, assuming the others are present in excess. You can probably assume that water was present in large excess.
3. The lowest of these yields is the theoretical yield.
4. The percentage yield is just your experimental yield divided by the theoretical yield, times 100%.

Author: Fred Senese senese@antoine.frostburg.edu

Copyright © 1997-2001 by Fred Senese
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Last Revised 02/23/18.URL: http://antoine.frostburg.edu/chem/senese/101-hidden/organic/faq/cracac3.shtml