Sriraman
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Ethyl acetoacetate in 4- Hydroxy oumarin synthesis
I have been synthesising 4-Hydroxy coumarin by condensing Aspirin acid chloride with ethyl acetoacetate in presence of Sodium hydroxide in aqueous
medium to give
sodium 2-(2-hydroxybenzoyl)-3-oxobutanoate. Recently I had another source of ethyl acetoacetate and the yields of
sodium 2-(2-hydroxybenzoyl)-3-oxobutanoate has come down to 30% of what I usually get. All analysis like GC, IR, NMR and residual acidity are same for
both ethyl acetoacetates. Can the method of manufacture of Ethyl acetoacetate (Claisen condensation of ethyl acetate Vs Diketene + ethanol )make the
difference.
Can some one guide me in this matter.
Sriraman
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Sriraman
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It should read as Ethyl acetoacetate in 4- Hydroxy coumarin synthesis.
Sriraman
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Sriraman
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Can some one guide me please
Sriraman
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Nicodem
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Guide you where?
| Quote: | | Originally posted by SriramanAll analysis like GC, IR, NMR and residual acidity are same for both ethyl acetoacetates. Can the method of
manufacture of Ethyl acetoacetate (Claisen condensation of ethyl acetate Vs Diketene + ethanol )make the difference. |
Essentially you are asking a question related to spiritualism and homeopathy in an organic chemistry forum. So you beter don't expect any serious
answer. Do you seriously believe a molecule bears the memory of the method of its creation?
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Sriraman
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Thank you for bringing philosaphy in to the forum. My objective of raising this question on Ethyl aetoacetate is that people have experienced such
problems. I was interested in knowing what type of solutions people have brought about - may be it is keto-enol tautomerism concept!.
Sriraman
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not_important
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keto-enol tautomerism differences of more than a small amount would show up in IR and NMR. Ditto for traces of the starting reagents, you could
intentionally add a starting ingredient to the EAA to see how much is meeded to show up in the tests.
What have you done to insure that the EAA supplier is the only variable? Do you still have some of the old, or can you get it again in order to do
side-by-side runs?
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Nicodem
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| Quote: | Originally posted by Sriraman
I was interested in knowing what type of solutions people have brought about - may be it is keto-enol tautomerism concept!. |
It can not have anything to do with tautomerism since you yourself wrote that your reaction includes "condensing Aspirin acid chloride with ethyl
acetoacetate in presence of Sodium hydroxide in aqueous medium". Even if your starting material contained any tautomeric excess (which
generaly don't last long given the half life of the keto-enol tautomeres is rarely more than half an hour at room temperature) it could have no
influence on your reaction since you deprotonate the acetoacetate anyway. Besides, like not_important told you, the tautomers give different NMR and
IR spectra.
In short, you are barking at the wrong tree. Your type of reaction is not susceptible to the quality of this reagent unless seriously deteriorated
(which it is not, according to your own analysis).
Has it ever occurred to you that the yields are not exactly a reproducible reaction factor? For certain type of reactions they can be pretty constant,
while for other types they can vary as much as +/- 20% or more. Not to mention that every chemist has its own nasty method of rounding up the yields
and that the yields cited in the literature are often for crude products.
[Edited on by Nicodem]
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Sriraman
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Is there a good review article on Ethyl acetoacetate, which I can refer to.
Sriraman
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Sriraman
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An interesting development took place, where by washing the Ethylacetoacetate with a weak base- I got back the yield. what does it indicate ?
Sriraman
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not_important
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Let's see - the reaction takes place in the presence of a strong base, washing with a weak base changes the yield. Residual acidity is the same for
both sources.
It suggests that you may not have enough strong base, that there's something dissolving in the wash water that the weak base may have not effect on,
that the water picked up during the wash affects the reaction, or that the reaction yield may just jump about with no changes in the reagents - run it
with the same reagents and conditions for 10 separate runs. Then run 10 more with pure water for a wash, then again with a bit of acid in the water.
[Edited on 21-5-2007 by not_important]
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Sriraman
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We tried only water washing. It marginally improved the yield. But when we tried fractionating the Ethyl acetoacetate under vacuum
a low boiling fraction 7-10% got removed and the rest distilled material gave the right yield. What can be the material in Ethyl acetoacetate which is
a low boiler reacts with weak base and
affects the reaction with Aspirin acid chloride ?
Sriraman
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not_important
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Couldn't say - what is th boiling point of the low boiling stuff, how soluble in water is it, is it neutral or acidic, and so on.
But you've established that the ethyl acetoacetate isn't very pure, if the spec says it shouldn't have that much other stuff in it you need to talk
with the supplier.
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Nicodem
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How large was the numerus of the trials for yield determination? Do you get a statisticaly signifact difference in the yields? What was the bp of the
low boiling fraction? Why was this impurity not visible on NMR if you say there is 7-10% of it?
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Sriraman
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We have carried out the washing with weak base up to 160 kg. About 5% of material is lost. But the yields have become OK.
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