Geocachmaster
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Ethyl acetoacetate with Mg(OEt)2 catalyst
I set out to make some ethyl acetoacetate, typically made by a claisen condensation of ethyl acetate. A base catalyst of sodium ethoxide is mostly
used. I don't have any sodium metal, but upon reading:
Quote: Originally posted by Nicodem  | | Magnesium methoxide is a substantially weaker base than sodium methoxide, particularly in nonpolar solvents, due to the higher acidity of the
Mg<sup>2+</sup> cation when compared to Na<sup>+</sup>. But in principle it should work as long provided the reaction times
are longer or conditions harsher. |
I went for a magnesium ethoxide catalyst prepared in situ by magnesium metal.
The orgsyn procedure referenced was scaled down and adapted. 25g of dry ethyl acetate (dried over CaCl2 for a week, then distilled), 1ml of ~99%
ethanol, and 1.5g of magnesium turnings/filings (1/2 molar equivalent of sodium with .2g excess) was added to a flask. A stir bar was added to
mechanically break up the Mg in case of oxide layer. It was refluxed for five hours . The amount of magnesium seemed to decrease, but this was
probably from more efficient packing of the turnings after being broken up. another five hours of reflux has left the amount of magnesium basically
the same.
Ten hours of reflux seems like a looong time for there to be no change, considering most Mg should dissolve when it's done. 12 hours of work has gone
into this, I feel it would be wrong to abandon now. But I dont wan't to waste my time either.
Are there any obvious problems? Should this work or does it not? If there are no definitive answers I will do another ten hours of reflux and then do
the workup, posting the results here.
Reference:
http://www.orgsyn.org/demo.aspx?prep=cv1p0235
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Magpie
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I made ethyl aceoacetate a long time ago using the procedure in Brewster (forum library). As I recall the formation of sodium ethoxide was rather
vigorous, not taking very long. All the sodium (or virtually all) was consumed.
If you are not seeing the Mg disappear I really wonder if you are forming any ethoxide.
The single most important condition for a successful synthesis is good mixing - Nicodem
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j_sum1
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As a quick test, why don't you measure the pH? That will at least inform you if nothing is happening at all.
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Cryolite.
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An issue with magnesium alkoxides is low solubility. I worry that even with good mechanical agitation breaking the oxide layer, the magnesium will
only react to form a surface layer of ethoxide, and this passivates the metal against further attack. I think you'll need a lot more ethanol in the
pot than just 1 ml, and maybe some iodine or mercury (gallium?) in there as well.
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clearly_not_atara
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I don't think magnesium alkoxides other than methoxides form easily. As you get to longer chains, the alkoxides of metals like lithium and magnesium
become more molecular and less ionic. This even happens with sodium t-butoxide which has reduced solubility and so KOtBu is preferred.
Mg(OMe)2 may nonetheless be enough for a Claisen on its own. It shouldn't be too hard to make methyl acetate?
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unionised
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From time to time I have wondered if you can make magnesium methoxide from Mg and MeOH, then add a solution of NaOH in MeOH to precipitate Mg(OH)2 and
get sodium methoxide.
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Geocachmaster
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j_sum1: I tested the pH, found to be between 8 and 9. When a few drops were shaken with water, it became cloudy and stayed that way. It appears that
there could be some alkoxide.
Cryolite.: I set the mixture refluxing again, figuring to leave it for most of the day. Another ml of ethanol was added too. This time I took a
picture first so I can make a good comparison. I wanted to add some iodine, but I don't have any (no gallium either ). I do have mercury, but I don't want do deal with mercury so it will stay as an element sample.
clearly_not_atara: And yes, of the magnesium alkoxides only the methoxide forms easily. But I think that the ethanol derivative should form with
refluxing. Maybe after this endeavor I will try for methyl acetoacetate.
Thanks a lot everyone
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Crowfjord
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Sometimes wet magnetic stirring doesn't work very well to remove the oxide layer. Grinding the magnesium granules against the flask with the end of a
glass stir rod has worked for me when dealing with a stuck reaction of Mg and methanol or Grignard formation.
If you have to start over, try first grinding your Mg with a mortar and pestle before the reaction, or better yet, magnetically stir the Mg in an
inert atmosphere for 24 hours before adding your ethanol (or ether and alkyl halide for Grignard).
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CuReUS
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why don't you try Ca instead of Mg ? http://pubs.rsc.org/en/content/articlelanding/1909/ct/ct9099...
"Ca can be purchased in pure form down at the pharmacy or in the vitamin section of the local hippie health food store " - strike 
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DraconicAcid
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If the magnesium isn't reacting, you can activate it with a small amount of iodine.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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clearly_not_atara
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What use could hippies possibly have for metallic calcium? That's a surprising thing to hear.
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Geocachmaster
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Okay so after four more hours of reflux (for a total of 14) noting much had changed. I filtered off the magnesium and let it dry. 1.38g left, a
difference of .12g. Subtract .02 for transfer losses and only ~.1g of magnesium reacted. This means a yield of no more than .4g of acetoacetate based
on estimated yield. I can't be bothered to do a work up because I would probably get nothing.
My first explanation is passivation, because only 1/5 of the ethanol I added reacted. I think I'll have to get some NaI or KI and try it again with a
small amount iodine to see if that helps.
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Cryolite.
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Maybe lithium would be worth a try if you have it?
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Geocachmaster
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I wish, no alkali metals here...
When I make some more money lithium and sodium are on my shopping list, although I'm 15 and have no job so it may be a while...
Doing experiments to find (more) OTC alternatives is fun though, I'll pursue this in the future.
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Cryolite.
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An interesting OTC extraction you could try would be extracting lithium metal from lithium AA batteries. The expected yield is about a gram per
battery, but that's about a seventh of a mole anyways, and with the scale you're running this at the small quantity of metal isn't an issue.
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byko3y
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You can't make magnesium ethoxide when there's water present. That's the basic knowledge a lot of authors mention. Addition of aprotic solvent into
ethanol makes the reaction even more difficult, requiring some strong magnesium activation.
unionised, I see no reason why it won't work. Still pretty much depends on access to a particular metal.
CuReUS, for example, I have no easy access to elemental calcium. In industry calcium is more difficult to make than both magnesium
and sodium, so I see no advantage in usage of calcium.
Cryolite, 1 g from 2.5$ battery? 1 g of lithium is equivalent to 3 g of sodium, so that's 800$ cost of 330 g lithium vs 1 kg of
sodium. In no way I see sodium to be less than 10 times cheaper than lithium, unless you are cooking meth and need specifically lithium.
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Cryolite.
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I never said that it would be cheap, but for a small scale experiment like this I don't see why lithium from batteries would be prohibitively
expensive. And also, sure sodium is cheap in bulk, but where are you going to buy some? It's sold on ebay, but if you would go that route you could
also buy lithium and that's cheaper per mole anyways.
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byko3y
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Well, I feel lucky to live in the place where you can buy 50 g of pure sodium for 2$. As I've said earlier, "pretty much depends on access to a
particular metal".
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Cryolite.
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Jeez, where the hell do you live and how can i move there? 
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BlackDragon2712
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50g of pure sodium metal at 2$ ?? ayfk?? I want to move there right now... do they sell online btw?
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Geocachmaster
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The cheapest I could get sodium is $6 for 50g, but that's only for 1 Kg. A more reasonable quantity of 100g would cost $15 per 50g. $2 for 50g is
insane, can you ship some to me?
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Nicodem
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Geocachmaster, if you can get magnesium, you should also be able to procure NaOH to prepare sodium ethoxide and do this reaction in a proper manner.
NaOH is still one of the bases easiest to get.
Unactivated magnesium is unlikely to react with alcohols diluted in organic solvents. Besides, regardless of what that younger Nicodem says, I think
that magnesium methoxide is too acidic to work as a base in this reaction. Unless maybe, if by harsher conditions he meant heating dry magnesium
methoxide in methyl acetate in a pressure reactor at >120 °C, or something crazy like that.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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