Preparation of GAA by azeotropical distillation

[Bandil]

Hi!

Around here, 99% acetic acid is no longer available OTC, which obviously is a very bad thing. 80% is however available in bulk and at a very low cost. I really dont want to make an acetate, isolate the salt, and then do the whole add sulfuric thing and distill.

Isn't it possible to mix 80% acetic acid and a minimal amount of toluene in a flask, and fit a dean stark trap + condensor? The BP of acetic acid is 117.9^oC. Won't the water/toluene azeotrope distill of at 85 ^oC? In theory this could be caught in the dean trap, and the water subsequently removed.

Then the remaining toluene could be distilled of in a usuall manner.

...or will everything come over as an ugly mishmash and ruin everything?

Regards
Bandil

[ragnaroekk]

Toluene forms an azeotrope with acetic acid:

B.Pt. toluene: 110.60°C
B.Pt. azeotrope: 105.40°C
Toluene in azeotrope: 72.00%

But you can distill the 80% acetic acid, the azeotrope formed with water boils at 76,6°C and contains only 3% acetic acid so your losses will be tolerable as you told the 80% acetic is plenty and cheap at yours.
You should get about 730 ml to 750 ml GAA from 1 liter 80% acetic acid this way. Sounds ok to me.
The distillate can be used for salad dressings.  

[Chromic]

The only way to get to 100% GAA is to form the acetate and distill from sulfuric acid. Sorry!

Distilling 80% AA, even with a really long column will not get you GAA. Distilling with a solvent that forms an azeotrope will, but it's too hard for a clandestine bee to do it (IMHO!).

Good luck!

[ragnaroekk]

The distillation will yield 98% to 99% acetic acid - GAA sufficient pure for almost all purposes is usually made by "freezing out" of the acid gained by distillation.

Vinegar cannot be distilled to yield GAA (or high concentration acetic acid in serious amoounts) - this is obvious from the azeotrope formed with 3% acetic and 97% water.

Another way to GAA from the 80% acetic would be to add ketene or acetic anhydride - more theoretical but it works.  

There is NEVER something like "the only way" in chemistry.....

[Chromic]

There is no azeotrope with GAA and water. I have posted the phase diagram in the past. I could post it again if necessary?

I mean the only way in clandestine chemistry--the subject of this board is to form the acetate and distill.

Sure mixing 80% GAA and acetic anhydride will work (after the AA hydrolyzes)... but if the poster had that, they'd also have GAA easily available. Ketene, yeah, it's OTC from acetone pyrolysis--but have you done this? It's actually fairly freaky.

Freezing out pure acetic acid won't work either. Have you tried this? I could not get it to work with 80% acetic acid. Go ahead. Try it and post back your results--but don't respond with knowledge gained thru academic knowedge on this subject!

My posts come from experience--not theoretical knowledge.

[ragnaroekk]

"There is no azeotrope with GAA and water"
- after several databases on azeotropes there is.

"Freezing out pure acetic acid won't work either. Have you tried this? I could not get it to work with 80% acetic acid."
- of course freezing out does not work well with 80% acetic acid. As I told before, you have to distill it before and freezing out is the last step to GAA. Freezing out is a little tricky as it needs patience for not to cool down to fast and to deep and to include water in the crystal lattice of the frozen acetic acid. Vacuum filtration is a "must do".
I used freezing out quite often in the past.

Reposting or linking to this diagram you spoke about would be highly appreciated.

regards
rAg

EDIT: After some deeper investigation onto this I came to the conclusion that "freezing out" is a useful way to concentrate acetic acid with an concentration over 95%.
But it actually seems that although acetic acid forms an azeotrope with water it is not feasible to distill this azeotrope out for what reasons ever, so simple distillation of the named 80% acetic is no way. Azeotropic distillation might be - benzene, chloroform, DCM should work, but after consulting some books of practical wisdom (written before 1900   ) I came to the conclusion that Chromic is right on the point when he says that the best way for concentrating the 80% acetic acid to GAA is by forming an acetate followed by distillation with conc. H2SO4.

[pericles]

Acknowledging that it's at least a touch offtopic, could you help out the less daring among us by elaborating on "freaky"? I'd been contemplating giving this a (very, very careful) try in the next few months, and any lessons learned would be helpful.

[Bandil]

Im quite sure that 97% acetic acid would be fine enough for the knoevangel condensations. As far as i can figure out, a simple distillation of 80% acetic acid would give 97% acetic acid? Is there any reason the remaining water cant be removed by using sodium sulfate or any other dirt cheap drying agent?

Its not a problem getting the real solvents, i just try to avoid the chem. companies whenever possible!

Regards
Bandil

[ragnaroekk]

No. I was wrong on the distillation - concentrating 80% acetic acid to 95%+ acetic acid wont work by simple distillation - using a water carrier like benzene would be possible but tedious and not practical as Chromic told.

Freezing out:
There is some confusion on this because there are two ways "freezing out" is used.
- First in the concentration of vinegar, whereby WATER is frozen out - this gives acetic acid with an concentration up to 30% - not more.
- Second, all acetic acid with an concentration over 95% can be frozen out whereby here the ACID is frozen and the water stays liquid and can be sucked off from a Buchner funnel with vacuum.

But Chromic was right: From 80% acetic acid to GAA the way is by the acetate/H2SO4 distillation.

Sorry.
RaG

[Barium]

I have no references for this so I might be talking out of my ass here, but shouldn't it be possible to bind most of the 20% water in 80% AA with sulfuric acid since it tends to hold on to its water rather strongly. Calculate how many mols of water say 500 ml 80% AA contains, add an equimolar amount of conc. sulfuric acid and distill off the AA. The sulfuric acid should be reusable by distillation if one so desires. Perhaps the distillation of the AA is best performed under reduced pressure?

[Novice]

Now there's an idea I like. I posted a similar (identical) idea a couple of weeks ago, but it got UTFSE-rated.

Question is if the sulphuric acid will do any damage to the AA... I don't know, only experiments will tell I suppose.

Unfortunately I've experienced that dilute sulphuric acid will not emit the water it contains upon heating/distillation, so recovering it is probably not an option (haven't tried vacuum distillation though).

The fact that I couldn't dehydrate sulphuric acid even on excessive heating only proves Bariums point though, let's just hope it won't do the same thing to AA.

[Barium]

AA should not be attacked under these conditions. You sure can remove the water from dilute sulfuric acid, but it requires quite high temps since it really holds on to water.

[Nicodem]

Question is if the sulphuric acid will do any damage to the AA... I don't know, only experiments will tell I suppose.

Sulphuric acid does not "harm" acetic acid, at most it might dehydrate it if sulphuric acid is in excess with water. In such case only some acetic anhydride might form.

Unfortunately I've experienced that dilute sulphuric acid will not emit the water it contains upon heating/distillation, so recovering it is probably not an option (haven't tried vacuum distillation though).

Off course it works. I used to concentrate 35% sulphuric acid when I needed it for the HCl gas generation. I just boiled the acid under low pressure of a water jet (don't forget the water trap!) and it concentrates it just perfectly. I never measured its density (concentration) but it was just perfect for HCl gas generation from 30% HCl. From the volume reduction I would guess it was above 85%. And the rests of this HCl dehydration can bee regenerated again if one has enough patience.

[Novice]

Well, then I screwed up when trying to distill it and I'll give it another go.

This however seems to be the most promising way of dehydrating the AA and I will definately try it out within a couple of weeks! I'll post whatever results I get from it.

[Novice]

Nicodem,

I never applied any vacuum, as I mentioned. I also started from 35-37% (d = 1,3 or so) sulphuric acid, and ended up with d ~ 1,6 (~70%), which I don't think of as concentrated sulfuric acid. So yes, in my case, some of the water did leave the solution, but the last ekv. of water is pretty damn protonated and stuck in the acid. And this seems reasonable since 85% (the approximate concentration of your acid) H₂SO₄ contains pretty much 1:1 H₂SO₄:H₂O.

[ragnaroekk]

NOVICE, if you should try this "dehydrating acetic acid by conc. H2SO4" please wear a gasmask or use a fumehood or at least a strong fan blowing the fumes away from you out of a window. CO is deadly you must know.

[Novice]

ragnaroekk,

Thank you, I appreciate your concern. I always use my 1 kW fan driven fume outlet whenever I'm going at it in the lab

You mention CO is deadly, and I wonder if you insinuate that CO is formed during distillation? Both Nicodem and Barium mention that the AA will not decompose or whatever, do you have some other information on this matter that we have not taken into account?

[ApprenticeCook]

1kW fan, now thats what i call a FAN!  

And CO generation... where is that coming from might i ask? if not decomp the AA wheres it coming from?? Rag??

[Rhodium]

Carbon monoxide is formed by dehydration of formic acid with sulfuric acid, not acetic acid.

[lugh]

As far as the original topic of this thread, see

Patent US2275802

and

Patent US2028800

for the proper approach    Another bee  friendly method from the past is CA 41 4445g (1947) using activated charcoal