Sciencemadness Discussion Board

Ethyl acetoacetate with Mg(OEt)2 catalyst

Geocachmaster - 7-4-2017 at 18:43

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

Magpie - 7-4-2017 at 19:29

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.

j_sum1 - 7-4-2017 at 19:32

As a quick test, why don't you measure the pH? That will at least inform you if nothing is happening at all.

Cryolite. - 7-4-2017 at 21:21

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.

clearly_not_atara - 8-4-2017 at 00:30

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?

unionised - 8-4-2017 at 04:17

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.

Geocachmaster - 8-4-2017 at 04:51

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:)

Crowfjord - 8-4-2017 at 07:27

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).

CuReUS - 8-4-2017 at 08:52

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:D;)

DraconicAcid - 8-4-2017 at 10:32

If the magnesium isn't reacting, you can activate it with a small amount of iodine.

clearly_not_atara - 8-4-2017 at 13:10

What use could hippies possibly have for metallic calcium? That's a surprising thing to hear.

Geocachmaster - 8-4-2017 at 16:06

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.

Cryolite. - 8-4-2017 at 18:47

Maybe lithium would be worth a try if you have it?

Geocachmaster - 8-4-2017 at 19:06

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.

Cryolite. - 8-4-2017 at 20:20

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.

byko3y - 9-4-2017 at 12:06

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.

Cryolite. - 9-4-2017 at 12:53

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.

byko3y - 9-4-2017 at 14:42

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".

Cryolite. - 9-4-2017 at 15:46

Jeez, where the hell do you live and how can i move there? :o

BlackDragon2712 - 10-4-2017 at 06:10

50g of pure sodium metal at 2$ ?? ayfk?? I want to move there right now... do they sell online btw? :o

Geocachmaster - 10-4-2017 at 06:22

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?;)

Nicodem - 10-4-2017 at 07:19

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.