BigTexas
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Ethyl acetoacetate synthesis: some questions !
I disagree with the old procedures that describes the preparation of Ethyl acetoacetate.
According to Org. Synth. 1926, 6, 36. Inglis, J.K.H., Roberts, K.C. the two reactions that might proceed if dry acetoacetate (with 3% in it and pure
Na metal are the following ones:
2 CH3CO2C2H5 + Na -----> CH3CONa=CHCO2C2H5 + EtOH
CH3CONa=CHCO2C2H5 + CH3COOH ----> CH3COONa + CH3COCH2CO2C2H5
In the second reaction the HOAc is added to make the solution slightly acidic.
Ethyl acetoacetate preparation
The yields are very low if this method is used (only 28-29% yield, based on ethyl acetate). That's why this method is performed in large amounts:
there is no way to distill ~10 mL ethyl acetoacetate if 100 mL flasks are used. Another remark is that there is one YouTube video about this
preparation and one additional problem was the formation of solid calcium acetate when CaCl2 was used as drying agent.
According to another article in reference 5 below: the yield is 75-76% if the excess EtOH which is formed is eliminated. According to that article the
reaction might be a dynamic equilibrium:
2 RCH2COOC2H5 + NaOC2H5 <===> RCH3CONaCRCOOC2H5 + 2 EtOH
The reaction time is higher: 8h at 78 degrees Celcius.
In addition the amount of sodium metal is way lower which makes this method even more interesting:
0,4 mole NaOCH2CH3
2,4 mole EtOAC
The problem is that there is a general discussion and I can't find the exact procedure. Does anyone have experience with the preparation of ethyl
acetoacetate in high yields ?
Where is the procedure ?
Another question is if it's possible to hydrolyse ethyl acetoacetate with aq. H2SO4 to form acetoacetate, followed by a spontanious decarboxylation
with formation of acetone ?
Any sources ?
I really appreciate any further help to discuss this matter more in detail. Why is the old method still used and fully described in literature, while
the last article is still somewhere on the background ?
How to prepare acetone with ethyl acetoacetate as starting material ?
Any experiences ?
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Magpie
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The only thing I can contribute is my experience making ethyl acetoacetate 9yrs ago. I used the procedure in Brewster (forum library) at roughly 1/2
scale, ie, 117 mL ethyl acetate vs 200 mL for full scale.
My yield was 13.3g for a 16.7% yield. The expected yield was 6.5g. I attribute this to the fact that I used vacuum distillation instead of
distillation at atmospheric pressure.
Yes, the yield is terrible.
The single most important condition for a successful synthesis is good mixing - Nicodem
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BigTexas
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Quote: Originally posted by Magpie  | The only thing I can contribute is my experience making ethyl acetoacetate 9yrs ago. I used the procedure in Brewster (forum library) at roughly 1/2
scale, ie, 117 mL ethyl acetate vs 200 mL for full scale.
My yield was 13.3g for a 16.7% yield. The expected yield was 6.5g. I attribute this to the fact that I used vacuum distillation instead of
distillation at atmospheric pressure.
Yes, the yield is terrible. |
Brewster's method isn't a good procedure. The reaction time is way too short and ethanol is added to decompose sodium metal.
That's the discussion: the procedure of McElvain removes the EtOH which is formed during the reaction with yields close to 80% (!).
The practical problem is to prevent the formation of sodium oxide and the fact that anhydrous EtOH is hygroscopic. In that case sodium hydroxide is
formed and this might interfere with this Claisen Condensation. This is a equilibrium: it's a clever idea to remove ethanol during the reaction.
Sources:
General discussion
The Acetoacetic Ester Condensation
This is the other (shorter) method, however this method results in low yields (25%) and much more sodium metal is used:
YouTube demo
Dehydroacetic acid is formed in trace amounts according to the literature when atmospheric distillation is used.
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Aqua-regia
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Hard job. You cannot better yield with this old methode. max 30-32%
Look this papers :
Alkyl Carbonates in Synthetic Chemistry. II. Condensation with Ketones. Synthesis of β-Keto Esters V. H. Wallingford, August H. Homeyer, David M.
Jones
J. Am. Chem. Soc., 1941, 63 (8), pp 2252–2254 DOI: 10.1021/ja01853a065
http://www.google.com.gt/patents/US2228452:
" diketene (37 g.) was heated under reflux on a steam bath (100 C.) with 40 g. of absolute ethyl alcohol and 0.3 g. of sulfuric acid for 3 hours. In
spite of the thermal instability of the polymer, a yield of 80-85% of ethyl aceto-acetate, boiling at 68 C. at 10 mm. pressure was obtained by washing
the reaction product with saturated salt solution, drying, filtering, and distilling under vacuum"
[Edited on 15-8-2016 by Aqua-regia]
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