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How do I compute yield for multistep synthesis (Cr(acac)3)?
- 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 (firstname.lastname@example.org)
You have to remove the (somewhat acidic) hydrogen on the central carbon in the acetylacetone before it will chelate to the chromium(III). 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,
- Obtain a net equation for the synthesis by combining the equations above.
- 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.
- The lowest of these yields is the theoretical yield.
- The percentage yield is just your experimental yield divided by the theoretical yield, times 100%.
Author: Fred Senese email@example.com