Sciencemadness Discussion Board - Synthesize ethylene glycol diacetate?

24% acetic acid is definitely not going to cut it for an esterification. You need to eliminate water. Use glacial acetic acid and a strong acid catalyst, and then reflux.

And you can concentrate yours by making acetate salt and distill with excess sulfuric acid.

Junk_Enginerd - 16-9-2019 at 10:40

It requires more than the most basic approach. :-)

Concentrated acetic acid plus sulfuric acid.

The acetic acid should well be in molar excess, say 4 times compared to the glycol. A few milliliters sulfuric acid would be enough (at a 100 ml scale). Requires refluxing for several hours. Then washing the water immiscible layer of the reaction mixture (ester) with dilute sodium hydrogen carbonate solution, then with water, then drying the ester with anhydrous Na2SO4, or MgSO4, then filtering, then distillation.
Well, this is a fairly basic approach for an ester synth.

Maybe there's an easier method, I didn't check.

Nice, very thorough, thanks. But also... why?

Lol, in all seriousness, I'd be very happy if you would explain the reasoning behind these steps. I think I have all the equipment necessary with some MacGyvering, and all the chemicals as well. I need very little of the ester, something like 2% of the final mix, so a little goes a log way.

So I gather that we're eliminating any and all water what with the glacial acetic acid and sulfuric acid.

And exactly what does refluxing entail here? I'm familiar with refluxing from alcohol distillation as a means to isolate a particular temperature fraction, but when you say "for several hours" it doesn't sound like the goal is to actually extract anything in this stage. Is it only to keep temperature at an absolute maximum?

And sodium carbonate washing is to remove the acids used to make it I presume, but why? If there's acid remaining, seems to me washing it with carbonate would leave a base instead?

Is the super thorough drying necessary because of hydrolysis? I've gathered that's what makes it function in the application. It slowly hydrolyses to acid which drops the PH of the silicate and makes it gel. Would CaCl2 suffice? I've got a 25 kg bag of that, but not MgSO4 nor Na2SO4, though I suppose either should be super simple to make from FeSO4(which is the most readily available sulfate I possess) with either NaOH or MgCl?

I suppose my initial experiment was sort of a success after all then? The immiscible layer is ethylene glycol diacetate?

DavidJR - 16-9-2019 at 10:59

Reflux = maintaining at/near boiling with the use of a condenser to avoid evaporative losses.

Usually esterifications with an alcohol and carboxylic acid don't really proceed at a noticeable rate at room temperature. The rate of reaction will increase with temperature. So, the boiling point is as good as you can get without a pressure vessel of some kind.

And sodium carbonate washing is to remove the acids used to make it I presume, but why? If there's acid remaining, seems to me washing it with carbonate would leave a base instead?

Yes, it's to neutralize the remaining acids and form water-soluble salts that are washed out. Acetic acid is probably pretty soluble in your target ester, but salts will not be.

Not only would excess acid be an impurity, it would also catalyse the hydrolysis of the product meaning it would be less shelf-stable.

Is the super thorough drying necessary because of hydrolysis? I've gathered that's what makes it function in the application. It slowly hydrolyses to acid which drops the PH of the silicate and makes it gel. Would CaCl2 suffice? I've got a 25 kg bag of that, but not MgSO4 nor Na2SO4, though I suppose either should be super simple to make from FeSO4(which is the most readily available sulfate I possess) with either NaOH or MgCl?

Calcium chloride isn't compatible with esters.

Hexavalent - 16-9-2019 at 11:11

So I gather that we're eliminating any and all water what with the glacial acetic acid and sulfuric acid.

And exactly what does refluxing entail here? I'm familiar with refluxing from alcohol distillation as a means to isolate a particular temperature fraction, but when you say "for several hours" it doesn't sound like the goal is to actually extract anything in this stage. Is it only to keep temperature at an absolute maximum?

And sodium carbonate washing is to remove the acids used to make it I presume, but why? If there's acid remaining, seems to me washing it with carbonate would leave a base instead?

Is the super thorough drying necessary because of hydrolysis? I've gathered that's what makes it function in the application. It slowly hydrolyses to acid which drops the PH of the silicate and makes it gel. Would CaCl2 suffice? I've got a 25 kg bag of that, but not MgSO4 nor Na2SO4, though I suppose either should be super simple to make from FeSO4(which is the most readily available sulfate I possess) with either NaOH or MgCl?

I suppose my initial experiment was sort of a success after all then? The immiscible layer is ethylene glycol diacetate?

The immiscible layer you saw is likely to be a small quantity of your desired di-ester.

Fischer-Speier esterifications involve an equilibrium between the reactant acid/alcohol and the product ester/water. According to Le Chatelier's principle, an excess of water in the initial mixture promotes the reverse reaction (viz ester hydrolysis) and will severely limit your yield.

The concentrated sulfuric acid serves two purposes; firstly as a catalyst, protonating the carboxylic acid carbonyl which facilitates nucleophilic attack of the alcohol, and secondly to sequester some of the water produced during each esterification reaction. Sadly sulfuric acid also catalyses the reverse reaction hence the removal of water is important.

Refluxing the reaction mixture here is exactly what you suggested: maximising the temperature of the reaction without loss of any volatile components.

Washing the organic layer during workup with aqueous base deprotonates any remaining acid. The resultant charged anion is much more soluble in water than in the organic phase and so is removed from the desired product.

The distillation of dilute acetic acid and direct preparation of glacial acetic acid has been discussed extensively on the forum.

Overall, your best bet would be to work from glacial acetic acid. Use a large excess compared to the diol, and if possible, have means of water removal during the reaction (Dean-Stark, molecular sieves, etc.).

It goes without saying that glacial acetic acid and sulfuric acid are both corrosive. Acetic acid vapours are hazardous and unpleasant. Ethylene glycol is metabolised to oxalic acid in the body and so has moderate oral toxicity. I don't mean to discourage you but I strongly suggest you gain some familiarity with fundamental theoretical and experimental chemistry before attempting these processes.

[Edited on 16-9-2019 by Hexavalent]

Junk_Enginerd - 17-9-2019 at 00:18

I see. So refluxing in this context could theoretically being as simple as boiling with a lid, or even in a pressure cooker? I mean, I'd probably use a cooled column regardless, just trying to understand it better.

Ah, I see. Thanks.

Calcium chloride isn't compatible with esters.

Noted, and thank you.

The immiscible layer you saw is likely to be a small quantity of your desired di-ester.

Oh yay, I successfully idiot'd it!

Fischer-Speier esterifications involve an equilibrium between the reactant acid/alcohol and the product ester/water. According to Le Chatelier's principle, an excess of water in the initial mixture promotes the reverse reaction (viz ester hydrolysis) and will severely limit your yield.

Good lord that's a lot of names and terms I know nothing about. Though I do know the ester hydrolyses, as it is a core mechanism in the way it's expected to work in the final silicate mix, so it makes sense of course that water in the mixture will ruin things a little. Is there some sort of equilibrium that is reached after a while or what? The mix with a small amount of ester I have standing now seems stable enough, and it did form to begin with, so I assume that something is currently stopping the hydrolysis?

Ah, so in "laymans terms" I suppose one could say it acidifies my weak acetic acid using a strong acid? For this purpose then, most strong acids would suffice? Of course it wouldn't be dehydrating like sulfuric acid which is also desired, so clearly sulfuric acid is a good candidate.

Refluxing the reaction mixture here is exactly what you suggested: maximising the temperature of the reaction without loss of any volatile components.

So as I mentioned above then, boiling with a lid is essentially the same, and using a simple pressure cooker would be taking it one step further?

Washing the organic layer during workup with aqueous base deprotonates any remaining acid. The resultant charged anion is much more soluble in water than in the organic phase and so is removed from the desired product.

Ah. Makes sense. Thanks.

The distillation of dilute acetic acid and direct preparation of glacial acetic acid has been discussed extensively on the forum.

Overall, your best bet would be to work from glacial acetic acid. Use a large excess compared to the diol, and if possible, have means of water removal during the reaction (Dean-Stark, molecular sieves, etc.).

I've been wanting to try that anyways so it'll be an interesting step. Seems like going the acetic salt route is the most convenient route, but I doubt that'll be an issue regardless.

It goes without saying that glacial acetic acid and sulfuric acid are both corrosive. Acetic acid vapours are hazardous and unpleasant. Ethylene glycol is metabolised to oxalic acid in the body and so has moderate oral toxicity. I don't mean to discourage you but I strongly suggest you gain some familiarity with fundamental theoretical and experimental chemistry before attempting these processes.

[Edited on 16-9-2019 by Hexavalent]

Of course. Not discouraged in the least, I do most of these types of things outdoors anyway. I've done quite a few processes involving NaOH, HCl, HNO3, chlorine gas, NOx, H2S and I'm still alive and kicking, so I think a few acids will be manageable. Thanks for the heads up.

[Edited on 17-9-2019 by Junk_Enginerd]

Tsjerk - 17-9-2019 at 02:32

If the ester is seperating from the reaction, it can be seperated in order to push the reaction to completion right? Probably not to completion but at least to the point where the concentration of ester becomes so low it stops separating.

No need for concentrated acid in that case.

Pumukli - 17-9-2019 at 02:54

Btw. ethylene glycol is an unhealthy compound. If you would touch it or its ester from time to time when dealing with the molds it might be better if you used 1,2-propylene-glycol, which is much less of a concern.

Herr Haber - 17-9-2019 at 03:28

Btw. ethylene glycol is an unhealthy compound. If you would touch it or its ester from time to time when dealing with the molds it might be better if you used 1,2-propylene-glycol, which is much less of a concern.

I dont know if there is a ban in the UK but APC pure doesnt seem to be carying ethylene glycol anymore and have the diacetate instead.

RedDwarf - 17-9-2019 at 05:05

I think you're rather overplaying the toxicity of Ethylene Glycol in normal usage. It's poisonous if taken orally and because it has a sweet taste (allegedly - I've never knowingly tried it, although I was climbing and drinking cheap wine in Austria at the time of the wine contamination scandal), it is seen as a risk for children or when added deliberately to other foods/drinks.
I've never seen anything about it being absorbed through the skin and based on the number of car mechanics who must have spilled the stuff over the years I think it's unlikely to be an issue. Just don't go sucking your fingers after using it or chewing on lumps of green sand (but you probably weren't going to do either).

Junk_Enginerd - 17-9-2019 at 06:16

Quote: Originally posted by Tsjerk

If the ester is seperating from the reaction, it can be seperated in order to push the reaction to completion right? Probably not to completion but at least to the point where the concentration of ester becomes so low it stops separating.

No need for concentrated acid in that case.

That's an intriguing point... Right now the layer is a little too thin to reliably separate with a syringe or similar methods. I guess a tall and narrow container would help in that case.

Ohh, one could have a tall narrow container, and inject more liquid from the bottom to make it overflow and just keep skimming off the top...

Well, this is simple to attempt. I've got the mixture standing so I could just see if more forms upon removal.

I've surely had worse. Besides, I don't want to touch the sodium silicate with any kind of bare skin regardless. That shit is mean on your hands.

Quote: Originally posted by Herr Haber

I dont know if there is a ban in the UK but APC pure doesnt seem to be carying ethylene glycol anymore and have the diacetate instead.

Ethylene glycol is just normal antifreeze though, right? The red kind, used in more modern engines.

[Edited on 17-9-2019 by Junk_Enginerd]

wg48temp9 - 17-9-2019 at 08:08

I want to make or otherwise acquire ethylene glycol diacetate, or diacetin, whichever is easiest.

The intent is to use it for self hardening/curing sodium silicate/sand mixes for making metal casting molds. If anyone knows of any other ester or acid that can perform the same job that'd be much appreciated too.

Usually CO2 gas is used to harden sodium silicate/sand mixtures. More accurately it carbonic acid produced when the CO2 dissolves in the water of damp silicate/sand mixture. I don't think the ester you want would work or if it does it would take a long time compared to the CO2 method. Why do you think it would?

Junk_Enginerd - 17-9-2019 at 11:53

Quote: Originally posted by wg48temp9

It is indeed. But I'm looking for alternatives. Part of the reason is that it can get a little unweildy with bigger molds, and I've had wildly varying results for reasons I don't understand. Sometimes it hardens perfectly, sometimes it doesn't at all, and sometimes it hardens but then it starts getting crumbly again for no apparent reason.

The other reason is I'm pretty passionate about science and engineering just for the sake of it, and I want to explore any and all possible options. Because I can, I guess. =)

I stumbled across this patent. For a patent, it's quite easy to follow, and I think the numbers speak for themselves.

Why do you think it would not work? The logic checks out for me. The ester hydrolyses when it comes in contact with the water in the sodium silicate solution, which should mean it releases an acid over time. A delayed release acid is the perfect thing to harden a sodium silicate mix.

According to the patent, depending on which glycol acetate is used, and the concentrations of them, the mix can be made to harden in anywhere from 10 minutes to several hours. As such, all I would need to do is mix sand, silicate solution, and some ester, make my mold, and then just put it somewhere for a short time and it's done. It sounds super convenient to me.

I gave it some more thought and I guess there's no reason quite a few other esters would probably work too. Based on the suggestions I got here, and due to the fact that my acetic acid ran out, I thought I'd try it with oxalic acid. It's quite closely related to acetic acid, so it should behave similarly. It also happens to be commonly sold as a solid, so no need to bother with driving out any water.

I mixed glycol and oxalic acid powder, and added some NaHSO4 to perhaps act somewhat as the sulfuric acid recommended earlier, part strong acid and part dehydrating. Since the glycol is very viscous without all that water in it, it's not very easy to tell how it's gone so far. Most of the ester still is yet to sequester, and it's quite cloudy, but as far as I can tell it's produced a lot more immiscible liquid this time around.

wg48temp9 - 18-9-2019 at 01:21