Sciencemadness Discussion Board - Making glacial acetic acid

Making glacial acetic acid

Runningbear - 5-10-2009 at 15:27

Hi guys,

Can someone suggest a simple method for making Glacial Acetic Acid. And also spell out any potential sticking points I may run into?

thanks in advance,

Runningbear

kclo4 - 5-10-2009 at 15:34

NaHSO4 + CH3COONa, that is, sodium acetate and sodium bisulfate, I hear is a good method.
I'd look around. Did you try searching for such a thing on this forum? I know it has been talked about before.

entropy51 - 5-10-2009 at 15:37

Search, Man! Lots of threads on AcOH.

NaOAc + H2SO4 distilled works fine, but it's not real simple.

So does keten + H2O, but you don't wanna go there.

Sedit - 5-10-2009 at 15:58

You caught me at the right time Runningbear as I was just making mention to someone a few minutes ago on the very subject. Good quality Glacial acetic acid cheeply has been a goal of mine for a while. Its easy to make but not so in large enough amounts that make it of much use unless one wanted to run a messload of "micro synthesis" just to get enough to work with.

Every method I have tryed so far needed a second distillation over MgSO4 before it was of good dryness BTW so keep that in mind.

You can use Sodium Acetate and react that with H2SO4 or Sodium Bisulfate. Using H2SO4 contaminates the AcOH with what I think is SO2 pretty easy if you heat it to much and the Bisulfate method is harder to produce decent amounts of AcOH at once because you need a decent amount of heat to push the dry distillation along. I must say though that after performing the following method I must say that all the 'dry' reactions suck and synthesis of an aq solution and extraction from that is just easier then dealing with the issues and expense of the other two.

I have recently been experimenting with the salting out of AcOH from an aq solution using IpOH. I have been making the concentrated AcOH solutions by reacting NaOAc with NaHSO4 and then adding IpOH. After the addition of a large amount of NaCl you will get an upper layer consisting of IpOH+AcOH with small amounts of Isopropyl acetate and H2O. Extract the upperphase and dry with MgSO4, filter this and distill off your IpOH to leave with GAA. The problem is I can not be 100% what I have it GAA because I feel there is some contamination of IpOH preventing it from freezing. Drying agent does not clump even after 48 hours so it is dry... just contaminated. When the AcOH starts to distill the distillate takes on a cloudy color and surface tension starts to present itself in the condenser which was not present during the IpOH prerun.

There is simular methods that use organic solvents which I will attach the references for and out of all the solvents I feel DCM has the best potential for its ease of aquisition. I would love for others to follow these synthesis along with me because I get very little time to play anymore and the anticipation of trying other methods is killing me

. Also because of the lack of focus I get I would like to hear the results from someone with proper fractioning of the IpOH and AcOH layer.

I got a little bit more data but I have to run at the moment, hear are a few papers someone gave me of interest.

Attachment: Separation_of_isopropanol_from_aqueous_solution_by_salting-out_extraction.pdf (256kB)
This file has been downloaded 2394 times

Attachment: SALT_EFFECT_IN_LIQUID-LIQUID_EQUILIBRIA_OF_ACETIC_ACID-WATER-BENZENE_SYSTEM.pdf (72kB)
This file has been downloaded 1448 times

BTW: I have been looking into the oxidation of EtOH to make the AcOH.... Anysuggestions? I seem to be producing a messload of Acetaldahyde and having it bubble out of solution.

[Edited on 6-10-2009 by Sedit]

entropy51 - 5-10-2009 at 16:33

Old acetic acid references

Suitable for the backyard shed.

A lot of this was worked out over 100 years ago:

http://www.archive.org/details/aceticacidvinega00londrich

http://www.archive.org/details/practicaltreatman00branrich

[Edited on 6-10-2009 by entropy51]

JohnWW - 5-10-2009 at 16:56

You can do a lot more, particularly by way of organic acetylations in synthesis, e.g. to protect -OH groups during other synthetic steps, if you prepared acetic anhydride, rather than glacial acetic acid. For most such reactions, which are reversible, the water produced by acetic acid, even with H2SO4 used as a catalyst, would tend to reverse the reaction. Here is the thread on the subject, which runs to 23 pages: http://www.sciencemadness.org/talk/viewthread.php?tid=9 .

Glacial acetic acid, in organic synthesis, has little more use than making acetate esters in reactions in which the desired product is immediately removed from the reaction mixture or is otherwise particularly favored, e.g. acetates of certain alcohols, as in industrial cellulose acetate and ethyl acetate manufacture; and, in inorganic chemistry, in preparing soluble acetates of some heavy metals that have few soluble compounds e.g. lead(II) acetate ("sugar of lead", Pb(CH3COO)2.3H2O, used in dyeing and paints), and use as a pH buffer in analytical chemistry as an alkali metal acetate or ammonium acetate.

[Edited on 6-10-09 by JohnWW]

Sedit - 5-10-2009 at 17:06

I don't feel theres anything loose about it Entropy. There is so much talk on the internet about these easy ways to GAA such as the standard NaOAc distillations yet I have seen few show results in practice. This should be a well defined area of this forum yet I don't feel it is and you can check this fact by going over the endless threads on this subject. Yes the oxidations of Ethanol have been mentioned a number of times in a variety of forms but since most of ya'll buy your GAA there is not enough practical discussion on the matter.

I know it is well understood processes but pulling it off correctly... and cleanly become another issue all together. I am meerly giving this fellow practical details of what to expect when attempting any of these synthesis other then just saying react Sulfuric with sodium acetate and your good to go.... because thats just not completely true in practice. I recently wanted more then 50ml-100ml or so and began exploring other options with salting out becoming the clear winner.

With all that said and done thanks for the books, I already started reading the first one and it looks like a nice easy to read text with alot of information.
Best regards,
~Sedit

[edit]
HaHa entropy I caught that edit before you had a chance to change it

[Edited on 6-10-2009 by Sedit]

entropy51 - 6-10-2009 at 06:05

Quote:

HaHa entropy I caught that edit before you had a chance to change it

That's because it was intended just for you to see!

I agree about there being too much confusion about making GAA, but the distillation of NaOAc and H2SO4 does work, just as the old books say it does. But the NaOAc does have to be anhydrous if you want strong AcOH. My AcOH comes out > 95%, but not glacial. There are some interesting things in those old books.

If you don't want to buy GAA, buy the indicating stop bath which is >90%. It's cheap and there's nothing suspicious about buying it. You can distill it to get rid of the pH indicator in it. Otherwise it's pure. It can be further dried by azeotropic distillation, and probably by other methods.

Sedit - 6-10-2009 at 14:21

It does work and works fine but doing it at a useful scale becomes troublesome.

I like the old style chemistry books like the one you linked to. I grew up reading ones like this from second hand stores and such and they are straight forward and easy to understand without to much technical jargon that some newer text like to jumble up there books with. I still haven't seen a non Pt based oxidation yet but still have more to read there as well.

The indicating stop bath looks like a good idea but I still enjoy the idea of trying to come up with a nice clean GAA synthesis that even the lowest of chemist(Me

) could make liters of cheeply. Producing liters of it from NaOAc and H2SO4 would not really be cheep or easy but I feel recovery of the AcOH dimmers from an (aq) solution could be done relativly cheep or easy. It that solution was made from the oxidation of EtOH it could be made very cheep.

entropy51 - 6-10-2009 at 14:58

Quote:

I like the old style chemistry books like the one you linked to

Maybe I misjudged you, Sedit! I'm a 20th century guy, but a 19th century chemist.

Quote:

I still enjoy the idea of trying to come up with a nice clean GAA synthesis that even the lowest of chemist(Me) could make liters of cheeply

I think that would be the ketene method, and you can also go all the way (to Ac2O).

Sedit - 6-10-2009 at 16:22

Quote:

Maybe I misjudged you, Sedit! I'm a 20th century guy, but a 19th century chemist.

An old hard back reprint of Antoine Lavoisier's work Elements of Chemistry is one of the things that sparked my interest in chemistry when I was like 9 years old in the first place. After that it was the 25cent used bookstore and antique stores sucking up all kinds of old books. The newer ones where to much for a young kid to grasp even if he is gifted in science but the older ones where well written and to the point performing simple but indispensable chemistry experiments. I have always considered that im a scientist in my mind and an alchemist at heart. Besides.... show me a newer chemistry book that details how to make all your own apparatus. Tinkering is half the fun.

The Ketene method has always drawn me to it but everytime I think I will do so the big flashing warning signes go off. Ketene isn't the most user freindly and heat plus acetone don't sound like a party either. One day I will do it but when that day comes I will know exactly what the hell Im doing and I don't feel I am completely there for that process yet.

Agreed though that is the ultimate in large scale GAA synthesis.

Runningbear - 6-10-2009 at 21:00

Sedit, thanks for the comprehensive post. I like the salting out method. i can find or make all the required chems. I'm going to give it a go. Can you tell me the starting percentages for combining NaOAc with NaHSO4 and how much IpOH should I add to this? And when you say a large amount of NaCl, how much are you talking about?

Also, I'm interested in the DCM method as I think it might keep a bit of water out. Can you elaborate a bit further on this method?

Runningbear

DJF90 - 7-10-2009 at 07:03

JohnWW - Acetates is the obvious use you may think of for glacial acetic acid, but in synthesis I would say its use as a solvent is much more prevailent.

Sedit - 7-10-2009 at 11:43

Quote: Originally posted by Runningbear

Sedit, thanks for the comprehensive post. I like the salting out method. i can find or make all the required chems. I'm going to give it a go. Can you tell me the starting percentages for combining NaOAc with NaHSO4 and how much IpOH should I add to this? And when you say a large amount of NaCl, how much are you talking about?

Also, I'm interested in the DCM method as I think it might keep a bit of water out. Can you elaborate a bit further on this method?

Runningbear

The paper attached talks about the equilibrium data you are looking for that pertains to the use of DCM and quite a few other organic solvents. DCM is not the best one to use at all but for me is the easiest and cheepest to obtain. The fact that it could be recovered so quickly and cleanly also makes the process much more attractive.

If you read thru it you will see it stated that the AcOH exsist in its dimmeric state(AKA glacial) in the organic solvant. I do not really believe this to be so when using IpOH but drying agents and the azeotrop between H2O and IpOH clears up the excess water. Also the IpOH salting out paper that I included in the first post talk about the use of potassium carbonate instead of NaCl which means that there would be less water in the mixture to begin with.

No word though on the concentrations of the AcOH solution at first though because I only added H2O to aid in dissolving all the reagents. This really didn't work well and In future works I am going to add the water and distill it to push any equilibrium in the direction of AcOH. The distillate will be salted out with various salts after that into DCM. I feel multiple portions of DCM should be used then combined before distillation for the highest recovery percentage.

Attachment: Mechanism_of_acetic_acid_transfer_from_aqueous_sodium_chloride_solutions_to_some_organic_solvents.pdf (388kB)
This file has been downloaded 1521 times

entropy51 - 7-10-2009 at 12:12

Quote:

When the AcOH starts to distill the distillate takes on a cloudy color and surface tension starts to present itself in the condenser which was not present during the IpOH prerun.

Sedit, what is the head temperature when the AcOH starts to distill? Thanks.

This is interesting, but it looks as messy as all the other methods! Still, if it works.....

Sedit - 7-10-2009 at 13:29

I dunno as did not have a thermometer on it when the AcOH started to come over. I was forced into a short path retort style distillation. The rubber stopper that held my thermometer in place shriveled and shrunk because of the Isopropylacetate(I assume) and screwed me up for finding the temperature before any AcOH came over. I just switched to something else and continued. Will not be hard for me to set something back up to get the temperature but I just haven't done it yet.

It will be a few days because im going out of town either tommorow afternoon or friday but I want to get right back on it as soon as I get back.

You are right though, it is a bit messy, but I have not streamlined it yet either. I was going to wait till I got everything simplified as possible before posting about it publicly but seeing as how Runningbear brought this up I thought I would make mention of it and possibly have a helping hand at trying various salts and solvents in the process as well as discuss some possible EtOH oxidations.(BTW the link you gave me says that they even have the same problem Im having where so much is lost in the formation of Acetaldahyde cutting yeilds down dramaticly)

You got them little trolls in the back of my head yelling Ketene in my ear once again. I keep telling them "No!, its to dangerous" but then they call me a vulgar name for a womans private area and egg me on even more.... Maybe I should try it... or get some medication to stop the voices

entropy51 - 7-10-2009 at 14:47

Stay away from ketene. Easier & safer to buy that stop bath and concentrate it if you have to.

I would try something that will separate from H2O better than iPrOH, like DCM, EtOAc? Just a hunch.

[Edited on 7-10-2009 by entropy51]

[Edited on 8-10-2009 by entropy51]

Runningbear - 28-10-2009 at 01:51

If I was going to purify indicator stop bath (85% acetic acid), what is the simplest method?

Is it worth making a dilute solution of ethyl acetate from a portion of the stop bath solution then fractionally distilling the ethyl acetate / water azotrope off?

Should I dry the indicator stop bath with sodium bisulfate or some other drying agent first?

Runningbear

entropy51 - 28-10-2009 at 06:40

Runningbear, you can distill the stop bath just to get rid of the indicator it contains, which remains behind in the pot. The stop bath I get is often > 90% AcOH. I find 90% AcOH works for many purposes, but not for everything of course.

You can azeotrope off the water with EtOAc, but it requires a fair amount of ester to remove the water. I believe butyl acetate is supposed to work better than EtOAc, but I haven't tried it yet. I haven't found drying agents to be very useful, other than distilling from over CaCl2 which increases the concentration but the effect is not huge.

Those ancient books I posted above give some of the old methods for concentration that might be worth a look.

If you haven't already, set up a titration method so you can follow the progress of any concentration method you try.

Runningbear - 29-10-2009 at 04:09

Entrophy, there were some great methods in that doc. I'm going to test a few of them.

I also found the following patent, which if it works as started, sounds like a really good simple method for final purification.

ACETIC ACID RECOVERY FROM AQUEOUS SOLUTION BY DISTILLATION AND CRYSTALLIZATION

Primary Examiner:
Yudkoff, Norman
Assistant Examiner:
Foster R. T.
Claims:

1.A process of dehydrating acetic acid containing up to about 20 weight percent water comprising cooling the acetic-water mixture sufficiently to crystallize a substantial portion of the acetic acid present, and vaporizing under vacuum the remaining mother liquor, said vaporization to occur at temperatures between the freezing point of acetic acid and the eutectic temperature.

EXAMPLE 1

100 ml. of acetic acid containing 6.07 weight percent of water was placed in a heat-insulated glass flask at 10°C. in liquid form. Agitation in the form of stirring was begun, and a vacuum pulled, thereby reducing the pressure so that crystallization was observed. At the end of 50 minutes, 76 percent of the material remained in the flask, being in the form of dry acetic acid crystals containing 0.36 weight percent water.

To compare conventional crystallization, 100 ml. of the same crude acetic acid was cooled in a flask to 0°C. with agitation. The crude crystals which resulted were centrifuged for 10 minutes. The product contained 2.4 weight percent water, with a yield of 62 percent acetic acid.

EXAMPLE 2

100 ml. of the same crude as above was cooled to 0°C. with an ice bath with agitation. After crystal formation, a vacuum was pulled, resulting in a pressure of about 10 mm. Hg, under isothermal conditions (0°C.). At the end of 60 minutes, 82 percent of dry acid crystals were recovered containing 0.54 weight percent water.

JohnWW - 29-10-2009 at 06:55

What is the number of that patent, and preferably a link, please?

gsd - 29-10-2009 at 07:05

Quote: Originally posted by JohnWW

What is the number of that patent, and preferably a link, please?

http://www.freepatentsonline.com/3677023.html

gsd

entropy51 - 29-10-2009 at 13:35

Runningbear, SC Wack posted that patent a couple of months ago. I gave it a shot with an aspirator and cold trap, not wanting to pump AcOH vapor into my pump oil. It didn't work under those conditions (15 mm Hg), but presumably would go better on pump vacuum. Let us know if you can make it work, it would be nice if it did!

Panache - 5-11-2009 at 06:05

I find these methods that people are trying to adapt rather well tricky and fancy and unnecessary. Just buy vinegar, convert it to the acetate, evaporate off the water. Dry it at 150 for several hours, it does not decompose, combine this with NaHSO4 in a 'dry' blender to intimately mix the salts, pour salts in to a 'dry' round bottom, tap in some conc sulphuric and distill. It has to be glacial, there is no water in the system.
Patience and thoroughness is simply the key here, not tricks.
A very simple test for glacial acetic acid is a few ml in a 'dry' test, a spatula end of calcium carbonate will only form a slurry with glacial whereas wet acetic will give off CO2. Add a drop of water to the slurry and whoosh, sort of, more like a slow whoosh.

Sedit - 5-11-2009 at 06:38

Quote:

It has to be glacial, there is no water in the system.

Sounds so good in theory don't it? But reality does not always run according to theory. Never once was I able to achieve glacial statues on the first run and MgSO4 was always added to remove the traces of H2O and the distillation had to be run again. We are talking countless times here not once or twice. Not to mention.... Have you ever tried it? Its a pain in the ass letting SO2 into the product to often, H2SO4 does the same. This is good for a few ml but after that it starts to become a real pain with localized over heating and incomplete reactions.

[Edited on 5-11-2009 by Sedit]

entropy51 - 5-11-2009 at 15:32

Quote:

Sounds so good in theory don't it? But reality does not always run according to theory. Never once was I able to achieve glacial statues on the first run

I have to agree with Sedit on this one. I've done this dozens of times. At the temperatures required for the distillation the H2SO4 decomposes the acetate and the distillate does indeed contain 2 - 5% H2O. This is the reason that all the published methods for this prep say to fractionate the distillate through a column.

I say this based on titrating the distillate, not on your CaCO3 test, though it sounds reasonable.

I just tried your CaCO3 test on some 96% that had not been redistilled. No bubbles. It required more than a drop or two of H2O added to produce bubbling. AcOH is a weak acid, not highly dissociated in concentrated solution.

I'll stand by a titration any day.

[Edited on 5-11-2009 by entropy51]

S.C. Wack - 5-11-2009 at 17:10

Quote: Originally posted by Panache

Just buy vinegar, convert it to the acetate, evaporate off the water.

As has been said before here in the relevant thread, vinegar is full of not-acetic-acid-or-water. Purification of either calcium or sodium acetate made in this way from the concentrated organic crap requires some wasteful recrystallizations. You need good stirring to avoid hot spots on addition of acid, and the best way to make this easier is to use a diluent such as...acetic acid...acid-washed oil, whatever.

[Edited on 6-11-2009 by S.C. Wack]

Sedit - 5-11-2009 at 18:17

Point made S.C thank you.

For anyone looking for only a few ml of AcOH then just do as a freind told me as it works quite well. Put the stove on a low heat with your Vineger and add salt until no more will dissolve. Its at this point you add IpOH. The isopropyl alcohol will seperate itself as the upper layer and yeild a mixture of acetic acid and IpOH.

the IpOH forms an azeotrop with water and careful distillation will take out the remaining trace amounts of water and the AcOH dimmer can be distilled at a later time.

If all else fails at this point just add some dry MgSO4 to make damn sure its dry before you distill and you have a "cheap" way to about 100ml of GAA albeit with a messload of bulk associated with it.

[Edited on 6-11-2009 by Sedit]

Panache - 5-11-2009 at 18:43

Apologies for my simplifications, they were not intended to cause confusion.

Firstly i should have said 'just buy dilute acetic acid solution'. In australia this manifests itself as 'no name' or home brand white vinegar. It is not a fermented product its just acetic acid in water.

Titrations are better than my quickie CaCO3 suggestion of course, there's no question of that.

As for this not working very well the first few times you try it or 'never at all' unfortunately i would have to say generally things get better as you do them. I don't believe you think glacial acetic acid cannot be produced by anyone anywhere with only H2SO4, sodium acetate and sodium hydrogen sulphate. If you are i would have disagree with you.

People must appreciate the patent literature for what its for. Its not peer reviewed, it has a completely different set objectives to that of journal articles. It aims to exaggerate how difficult life is without this new bell and how well and good life could be if only everyone had one of these bells. It generally also concerns itself with how one would go about making 500,000 of these bells. I appreciate 'hotspots' would be a real concern if doing these things on a multi tonne scale but in a sedate 1L flask i think it's manageable.

Sure fractionating it would be more ideal, but really i can't see the problem.

And yes i have done it, both with acetic and propionic acids, however the latter is less problematic to get dry.

Lastly adding MgSO4 doesn't remove any water, merely binds it reversibly to another site. Works great for somethings but not very well for the last bits of solvation water from this system. The acetate does not decompose below 150, so use an oil bath for the distillation if you're having trouble regulating temperature and never let it go past 150.

Sedit - 5-11-2009 at 20:22

"Lastly adding MgSO4 doesn't remove any water, merely binds it reversibly to another site. Works great for somethings but not very well for the last bits of solvation water from this system"

Try it. Its about the only way to get decent yeilds out of H2SO4 of Bisulfate methods. Everything else is just spinning your wheels and waiting for your heating mantal to reach that high temperature.

JohnWW - 6-11-2009 at 00:16

What sort of impurities does naturally-brewed vinegar contain, i.e. other than acetic acid and water? I would think that propionic acid, propionaldehyde, acetaldehyde, ethanol, n-propanol, and sodium and potassium acetate, would be most likely. There could be traces of butyric acid, butyraldehyde, n-butanol, formic acid, formaldehyde, and methanol, the last three being toxic in larger amounts.

entropy51 - 6-11-2009 at 06:37

Quote:

I don't believe you think glacial acetic acid cannot be produced by anyone anywhere with only H2SO4, sodium acetate and sodium hydrogen sulphate. If you are i would have disagree with you.

I would appreciate it if you would post your procedure in detail then. I will quickly become a convert to your point of view if it works as well as you imply!

My opinions are not based on patent literature, but on dozens of experiments I have tried over several years.

Panache - 10-11-2009 at 16:39

I would appreciate it if you would post your procedure in detail then. I will quickly become a convert to your point of view if it works as well as you imply!

I already did in a post in this thread on the previous page. Some finer detail though. Do grind the acetate and sodium hydrogen sulphate together in stoiciometric ratios until you have a very fine intimately mixed powder that has begun to smell of acetic acid and is beginning to appear damp. The sulphuric acid is really just to act as a solvent of sorts and as a heat transfer agent. I find it doesn't heat up the powders very much when added. I just cover the powder with enough.

Additionally i use a vacuum, this helps enormously but it is not important whatsoever as i used to never use a vacuum. It speeds things up. i use a stillhead vertical setup for this one. I intially have the conc sulphuric in the stilhead resovoir. that way everything can be assembled and the sulphuric run in and the system run under reflux for a time before taking a your acetic acid. The vacuum negates the need for a drying tube however if not running under vacuum do use a drying tube.

Is that enough detail, i only did this over the weekend so i have it fresh in my memory, previous to that i hadn't done it for some 18months.

entropy51 - 10-11-2009 at 18:53

Thank you, Panache. Could you give your mass ratios, please? They might be critical for getting honest to goodness glacial AcOH? I've found this prep to be fairly tricky! Thanks again!

Sedit - 10-11-2009 at 19:15

I was running pretty much the same exact thing Panache and it always worked fine on smaller runs but when I tried to scale up to get larger amounts it was just one problem after another and I later just went to mixing them "wet" as a paste and distilling. I would then allow the distillate to clear up because it would always be cloudy yet after a day or so a scum would form on the surface leaving a clear distillate.

Addition of MgSO4 in liberal amounts and left over night would suck up the last of the H2O and a quick filtering and redistilling over fresh MgSO4 would produce clear dry acid.

I always found the main issue to be heat transfer and over heating more then the reaction itself. Thats the reason I started looking into ways of recovering AcOH from aq solutions.

This is one of the few things I did keep pretty detailed notes of and if I manage to fine the notes as Im attempting to recover all my files from a failed hard drive I will post some better details.

Entropy getting NaOAc fully dry is a bitch so there is a good possibility that is where the water was comming into the equation. Whatever the cause I suggest for anyone to just pass the distillate over dry MgSO4 and not mess with the fuss of trying to get GAA in one pass. It produces a cleaner product that never has the harse sulfur oder that dry distilling produces.

Panache - 11-11-2009 at 00:22

my supermarket now sells molecular sieves, i guess these should do a pretty dandy job also.

entropy51 - 11-11-2009 at 08:16

Quote:

Entropy getting NaOAc fully dry is a bitch so there is a good possibility that is where the water was comming into the equation. Whatever the cause I suggest for anyone to just pass the distillate over dry MgSO4

Sedit, drying NaOAc is not that difficult, just not any fun! Drying in a vacuum dessicator over silica gel removes about 2 molecules of H2O by weight. Melting carefully with constant stirring removes another molecule; it seems to be nearly anhydrous based on H2O loss. I also have the real stuff that I can use for check runs and I see no difference in H2O content of the AcOH that distills.

My experience is that attempting to dry wet AcOH on MgSO4 doesn't dry it significantly, based on titrating the AcOH before and after. But I'm glad that it works for you.

Sedit - 11-11-2009 at 13:16

I have enough NaOAc to attempt another run to document to show my process but it may be a while since I have alot going on at the moment and my camera is missing as well but first chance I get I would like to go indepth with both methods as a means to compair yeilds. I want to do the extraction from an aq solution using DCM and I will rerun another Sodium Bisulfate and NaOAc. From the initial test I think that the aq extraction is going to prove higher yeilding and cleaner then when using acid on NaOAc.

PS: The MgSO4 works best if you let it sit there for some time possibly two days in a closed container. At that point you will see the MgSO4 not only clumped up but some will be in needle like crystals precipitating out showing that it absorbed ALOT of the water now completly locked away as the hydrate.

Sedit - 17-11-2009 at 15:16

Materials
300ml 5% AcOH Saturated with NaCl.
70ml of 70% IPA saturated with NaCl.

Procedure
Mixing of the two solutions showed no seperation of layers and after extra NaCl was added it still showed only slight signs of seperation.
MgSO4·7H2O was employed to further saturate the solution some more to aid in seperation. Obviously Anhydrous MgSO4 is more desirable but I used it all up and have not made more yet.
This proved effective and approximately 20ml of IPA/AcOH seperated out of the 370ml mother liquor.

Mild tragedy strikes as 1 single drop of water fell into the 20ml after washing the other glassware and having a single drop fall into the solution. Should not be to much of an issue though considering that it should form an azeotrop with the IPA and leave as im burning it off.[note 1]

I ignited the 20ml in a Stainless Steel container nestled in an icebath and allowed it to burn out(I feel a bit premature due to the wind)to yeild 7.5ml of slightly yellow liquid with faint hint of IPA.
This was placed in the freezer till chilled to no avail so it was once again taken outside and ignited.
This left me with a mixture that would no longer ignite at about 4ml of now much darker colored liquid.
Placing this in the freezer for only a couple minutes it was obviously much thicker consistancy then before and was simular to thin cough medicine or a thick sugar solution clinging to the sides of the test tube.
It still failed to crystalize on refridgeration.[note 2]

Notes
1: This is obviously not the best way to go and distillation is the prefered methods but Im just running a fun small test and did not feel like getting that involved. Plus it proves a point in that it will cease to ignite once the IPA leaves the system.
2: I would thing it be prudent to add anhydrous MgSO4 and filter prior to distillation.

Discussion:
Well it all pretty much came out of a fit of bordem since I was off work and had the house to myself for a change which left me with an itching desire to do something but since I live in bumblefuck without a store to even go to for a few miles I decided to see what I could play with. I wanted to see if it can be done and to what effect could be yeilded from such a dilute solution. 4ml of not quite anhydrous, or more probable tainted with IPA, Acetic acid sounds pretty bad but basing it more on the idea of how much a given amount of IPA will extract for a given volume does not work out extremely bad given the extreme dilution of the starting solution. Also since only a single extraction instead of the prefered two maybe three shown from previous experients means yeilds could atlest double if not more. I will more then likely not partake in another attempt to extract such a dilute solution again but I do feel confident from the experiment and those prior that a bottle of IPA and a gallon of 5% could yeild about 150ml of Glacial acetic acid if one where determined enough. I perhaps will attempt this one day just for shits and giggles but more then likely not for a while since I want to focus more on concentrated solutions.

Panache - 23-12-2009 at 03:49

Ok i tried this today using ~600g of calcium acetate and i now understand what sedit and entropy were talking about, nothing happens, well that how it seems it goes so painfully slowly. In all the damm thing took 10hrs to distill over the ~450mL (and no i have as yet not titrated it). Made me think this would go so much better with a carrier gas instead of vacuum but you have all those issues of ensuring you manage to condense it out. Anyway at about the 7hr mark i suddenly realise this would go infinitely faster on the roto vap, every if i allow for the tedious drying of it. Anyway i have now replaced the 500ml bottle of glacial acetic i dropped earlier in the year, it can sit with my other stuff until i manage to drop it again in a few years.

IMO using NaAcetate is better than the calcium, albeit the calcium is reportedly easier to dry, i find both salts dry wonderfully well in a convential microwave, they don't appear to have much of a cross-section for the adsorption of the frequencies used in conventional ones, which i believe are tunned to water (and thats why feathers don't heat up in the microwave, unless they are wet). Once the water has left you can run the microwave forever and the only thing that happens to the salts is they cool down, even through 'heating'. During drying i tend to open the door every thrity seconds and blast it with compressed air to remove the after vapour as the fans in microwave are pathetic. In all it took some 15minutes to dry the 600g of Ca acetate i used, which beats the shit out of oven drying. I acertained the dryness by placing some in a dry cold testtube and heating until redness. if there is hydration water remaining you can clearly see it as a condensate at some point on the testtube, proved one only heats the bottom of the tube.

entropy51 - 23-12-2009 at 06:57

Panache, thanks for that tip on microwave drying NaOAc. I will definitely have to try that.

Magpie - 23-12-2009 at 11:18

Quote: Originally posted by entropy51

Panache, thanks for that tip on microwave drying NaOAc. I will definitely have to try that.

I second that. This could be a good way to prepare anhydrous NaOAc for use in making Ac2O.

Sedit - 23-12-2009 at 11:58

Third

.

Panache, Did you use Bisulfate to "dry" distill the AcOH out or did you use H2SO4? If you used Bisulfate I suggest adding some H2SO4 and stir it to a slush first to aid in heat transfer or else you will have many many problems. The time issue you see is why im starting to resort to aq extraction of the AcOH instead. I have gotten it now to the point where it is not as messy as when I first started experimenting but it still requires a few steps. The best part about the aq extraction though is that you can add drying agent while its still in the non polar with ease to make sure its dry before you distill it.

I would like to heat a report of it passing the Glacial test because I have a very hard time getting it to do this on the first run and resort to adding MgSO4 to the AcOH and slowly redistilling just above the temperature of AcOH to not release the water trapped in the MgSO4. After this you should be able to get it to crystalize to its dimmer with relative ease.

Congrates on the Synthesis though. No matter how long it takes or how annnoying it may be i still feels like a good accomplishment when completed.

blogfast25 - 25-12-2009 at 09:00

Merry Xmas (to those that way inclined)!

Very interesting thread. With this bad weather my attention was drawn also to isopropyl alcohol (propane-2-ol or IPA) as a major component of screen wash. I thought perhaps of esterification with acetic acid to isopropyl acetate. Of course that requires both reagents to be relatively water free: glacial acetic acid and relatively pure IPA.

My 'Tesco brand' screen wash doesn't mention composition of course. I measured the boiling point of the liquid using reflux and a calibrated digital thermometer to be 94 - 95 Celsius. IPA's boiling point is 82.4 Celsius, so the screen wash must contain considerable amounts of water (and perhaps also glycol?), perhaps as much as 50 w%?

A better idea of IPA content could be obtained by oxidising the secondary alcohol to acetone with a known quantity of potassium dichromate and back titrating the excess dichromate.

Rectifying the screen wash to 'pure' IPA could be an interesting exercise in fractionated distillation: there appears to be no IPA/water azeotrope but the fairly close BPs would require quite a few theoretical plates.

Oooops! There IS an IPA/water azeotrope at 87.9 w% IPA:

http://en.wikipedia.org/wiki/Isopropyl_alcohol

[Edited on 25-12-2009 by blogfast25]

JohnWW - 25-12-2009 at 12:23

Perrys Chemical Engineers' Handbook, chapter 13, also mentions that constant-minimum-boiling-point azeotrope, but lists it as having 31.46% water and 68.54% isopropyl alcohol. It is possible that some additional concentration may be obtainable by distillation with benzene or something, in a similar way to purification of ethanol above its azeotrope of 89.43%. Isopropyl alcohol is sold as "rubbing alcohol" at a concentration of about 70%.

Panache - 25-12-2009 at 13:20

Quote: Originally posted by Sedit

Third

Yeah its glacial. However i cheated and combined greater than equimolar bisulfate and around 200mL of glacial i already had. Initially it worked great and the first 250mL came over with little effort, the next 10mL took an hour, i then added around 100mL conc h2so4 (around 200g worth), the remainder of the distill took several hours of cycling between full vacuum and no vacuum. Sorry to not have mentioned the drying of the sodium acetate before, i thought everyone knew!!

blogfast25 - 26-12-2009 at 07:07

Quote: Originally posted by JohnWW

Perrys Chemical Engineers' Handbook, chapter 13, also mentions that constant-minimum-boiling-point azeotrope, but lists it as having 31.46% water and 68.54% isopropyl alcohol. It is possible that some additional concentration may be obtainable by distillation with benzene or something, in a similar way to purification of ethanol above its azeotrope of 89.43%. Isopropyl alcohol is sold as "rubbing alcohol" at a concentration of about 70%.

Wikipedia mentions cyclohexane as an azeotroping agent in it's IPA entry. Presumably distilling the 87.9 w% azeotrope with cyclohexane separates a cyclohexane/water azeotrope and the dry IPA.

Yes, rubbing alcohol is another OTC containing IPA.

entropy51 - 26-12-2009 at 07:45

You can buy 91% (or higher) IPA at the drugstore. There are threads here on removing the last of the water, even to anhydrous. Search and you will find.

There are also posts lurking here about making esters in aqueous reactants. It definitely works for making ethyl acetate.

blogfast25 - 26-12-2009 at 09:17

Quote: Originally posted by entropy51

You can buy 91% (or higher) IPA at the drugstore. There are threads here on removing the last of the water, even to anhydrous. Search and you will find.

There are also posts lurking here about making esters in aqueous reactants. It definitely works for making ethyl acetate.

Buying stuff like that here in Britain from a 'farmacy' can be tricky w/o prescription, it's a real Nanny State when it comes to chemicals. What's the 91 % grade used for? Rubbing alcohol?

What about spray cans of windshield de-icer, wouldn't that be mainly IPA (apart from the driver gas)?

entropy51 - 26-12-2009 at 09:25

Quote:

Buying stuff like that here in Britain from a 'farmacy' can be tricky w/o prescription, it's a real Nanny State when it comes to chemicals. What's the 91 % grade used for? Rubbing alcohol?

In the US, it's normally on the shelf next to the 70% rubbing alcohol. No prescription needed.

Over here they also sell Iso-Heet in the hardware stores, used to prevent gasoline lines from freezing. It with the auto supplies, and is essentially anhydrous IPA. You can dry it and distill if need be. The other Heet product is near pure methanol, so read the labels. I have no idea if this is available in the nanny state, but I'd sure look.

bbartlog - 17-3-2010 at 19:43

After doing ethanol and water distillation I was so pleased with my 300mm Hempel column that I decided to take a stab at separating acetic acid and water by mere distillation. I did the following:

Added 248g of anhydrous sodium acetate to a 2l RBF
Added 331g of 31%HCl (aqueous) to this, and stirred briefly
Heated this at reflux for 45 minutes
Began distillation. Over a period of a few hours, 149g of distillate passed over. The head temperature never went over 100C, and the ratio of liquid dripping back into the flask to that coming over was about 3:1. At this point I was dismayed by the very strong vinegar smell of the distillate, and decided to examine the result.

Titration of the distillate with 1M Na2CO3 indicated that it was about 24% acetic acid

. After weighing other constituents I concluded that the acid remaining in the RBF was likely no more than 56% on net (considering the entire flask contents), although settling seemed to result in separation of a salt+NaCl layer so that the acetic acid on top was more concentrated. I poured off this top layer, which amounted to 107g, and set it aside for later drying and/or evaluation.

Sooo... why are acetic acid and water *so* hard to separate by distillation? They do not form an azeotrope (apparently), and while the separation in boiling points is not huge (118C vs 100C) I've achieved fairly clean separations of various other fluids with similar differences in boiling point, like the aforementioned ethanol and water. I thought about this a bit after looking at the way the liquid composition boiling point curve and the vapor composition dew point curve separate and come together for an azeotrope.
Is there such a thing as a 'near azeotrope', where a pair of such curves drawn for the range of mixtures had neither intermediate maximum nor minimum, but the curves still deviate from a straight line to the point where the boiling temperature remains *close* to the minimum over an extended range of mixture compositions? For example, when boiling 50/50 water:acetic acid, could the boiling point be much closer to 100C than to the linear interpolation of 109C?
Or is it more likely that I had problems because the water/NaCl phase in my RBF formed a separate phase, which being a saturated brine had a boiling point above that of plain water? I'm skeptical of this explanation just because most of the separation occurs in the column, after the solutes are no longer relevant.

All in all somewhat disappointing (even if what I poured off is fairly concentrated acetic acid I'll still only end up with about 50% of theoretical yield), and it's not like a few tweaks to the column will make much difference (I figure it's the equivalent of about six plates when used properly, which would suggest 20+ plates equivalent to achieve decent separation of acetic acid and water...

)

Magpie - 17-3-2010 at 20:13

The liquid-vapor equilibrium curves for the water/acetic acid system are close together. Ie, the relative volatility is close to 1. So while there is no azeotrope per se, the number of "theoretical plates" required for separation by fractional distillation may indeed be high.

My graphical estimate indicated 16 theoretical plates are required when starting with 4 mole% acid. Starting at 20 mole% acid or higher in the pot should be a great help.

There's a lot of information and experience here:
http://www.sciencemadness.org/talk/viewthread.php?tid=2194&a...

[Edited on 18-3-2010 by Magpie]

[Edited on 18-3-2010 by Magpie]

starman - 2-4-2010 at 14:59

Quote: Originally posted by Panache

(cut)... The acetate does not decompose below 150, so use an oil bath for the distillation if you're having trouble regulating temperature and never let it go past 150.

I've run this a few time now.Each time using 1-2 mole acetate and approx 2 times excess H2SO4 in a 1 litre flask.I find it difficult to drive off all the acid at this temperature restriction,with the pot still smelling very strongly of acetic acid and yeilds of only 60%.

My last attempt where i allowed the pot temperature way up did in fact lead to some type of decomposition as I was getting a fraction at about 150C.Seemed waxlike and mostly deposited in the condenser.Any idea at what this could be?(acetate and acid both reagent grade).

Any hope of improving yeilds and recovery?My initial thoughts are to use a smaller flask for the pot but I worry at the initial vigourous reaction.Or perhaps apply (aspirator) vacuum when the distillation stalls.

Comments and suggestions appreciated.

rrkss - 2-4-2010 at 20:55

I've always heated my acetate + H2SO4 flask until distillation stops somewhat ignoring the temperature. Should not decompose until well into the 400 degrees Celsius range since anhydrous acetate melts in the 300 range. I do find that my product is very contaminated with Sulfur Dioxide and requires further treatment with anhydrous copper sulfate to dehydrate and remove the sulfur dioxide.

I've given up this route to glacial acetic acid because it is too much hassle since I found a biodiesel supplier supplying ACS grade Glacial Acetic Acid for dirt cheap.

Panache - 7-4-2010 at 09:45

Quote: Originally posted by starman

Quote: Originally posted by Panache

(cut)... The acetate does not decompose below 150, so use an oil bath for the distillation if you're having trouble regulating temperature and never let it go past 150.

its slow tedious and shit but that's tthe best way i've found to ensure purity, definietly use a vacuum and have your oil bath on 150. Believe me it will still only come over sedately. Using a 5l flask it takes 8hrs to get ~1L glacial. After about 4hrs, cycling the vacuum on and off really helps.
I have been trialling a new method using citric acid(anhydrous) and sodium acetate, the two are combined, well ground in a blender then packed into a cromatography column. The column leads into a collection vessel that is protected with a cacl2 tube. On top of the tightly packed column i inflate a large double ballon with dry argon. I leave it in the corner and forget it, occasionally reinflating the ballon. Thus far it isn't working great but i need to have a proper look at it, there's approximately 1/3 of the expected glacial through in around 10days however it must be tested. If it doesn;t get better i will try hot argon as a carrier gas, this should work well. In theory some water in this system should help things along without getting into the final product as long as everything is kept below 40C as the trihydrate of citric acid forms and is an excellent dessicant.

starman - 7-4-2010 at 16:58

Interesting Panache.You must keep us updated on that one.I've been looking at anodic oxidation of ethanol.Apparently its been pretty sucessful with platinum or gold and I'm wondering if PbO2 coated lead has the required overvoltage to get the job done.

Jimmymajesty - 1-6-2010 at 07:13

Has anyone here tried to separate butyl acetate + acetic acid mix by distillation with a column?

I failed many times... it cannot be that hard

Here is what I did:

Bought a paint stripper OTC with the following composition on the label: butyl acetate ~60w% butanol ~20w% acetone ~20w%

I shook the paint stipper with water, after the extraction the water had an alcoholic smell, but no acetone. I also fractionated the mixture, but only one component could be detected. with a B.P. of 124°C... so the stripper is mainly made of butyl acetate.. I presume..

In the next step, i took two litres of "acetic acid escencia" which is sold in my country in supermarkets, and it is 20w% acetic acid + some organic crap, and I azeotroped the water off by means of the stripper + a dean stark.

Then I poured the water free butyl acetate (?) and acetic acid mix into a RBFL for fractionation, and started to separate them.. but no matter what I did... I adjusted the reflux, the temp of the reboiler, even replaced the packing in the column, I got the same result every time... a liquid with a strong smell of acetic, but it is not totally miscible with water, IIRC 50v/v% is lighter than water and floating on top like hexane, and has a stong smell of.. nail paint..

I am a bit puzzled any help would be appreciated!

Sedit - 4-6-2010 at 09:13

Has anyone any experiance with the acid hydrolysis of Vinyl acetate? Its used in alot of wood glues as the polymer and as a better source I believe would be spackles which is composes around 68% of the spackle the remaining being light organics and water mostly. Drying the spackle produces the polymer I belive so removing water would be no problem.

Just curious if anyone has tryed even dilute AcOH from PVA. I believe it has been mentioned but never heard of anyone attempting it.

The WiZard is In - 4-6-2010 at 12:45

Quote: Originally posted by JohnWW

It is possible that some additional concentration may be obtainable by distillation with benzene or something,

----
Tis - it is claimed - done this way on an industrial scale, Azeotropic
distillation.

By da Thorpe sez you can get from 4% vinegar to 40 by freezing,
without loosing flavour.

[Edited on 4-6-2010 by The WiZard is In]

Ephoton - 5-6-2010 at 22:43

thats real handy for pickeling my chillies wiz thanx
and octopus

[Edited on 6-6-2010 by Ephoton]

Sedit - 6-6-2010 at 10:01

But we have discussed these means Over and over again in the past many many times.....

What about Vinylacetate hydrolysis? If the price is right on the PVA or Vinyl acetate product this could prove rather cheep and not really bulky either.

mr.crow - 6-6-2010 at 11:12

you can also produce acetic anhydride from vinyl acetate. No one has gone into detail on this forum but I have a reference in the reference section.

Sedit - 6-6-2010 at 11:45

can you PM me a link please? ill look on the SE but if you know where its at then that might be quicker.

Jimmymajesty - 23-7-2010 at 10:23

Sedit you have you managed to make acetic acid by ageing the alcholod with dilute nitric acid?

I managed to decompose the denaturating agent by keeping the diluted alcohol + HNO3 mixture at 60°C for a day, but again, nothing acetic.

Sedit - 23-7-2010 at 11:38

Never tryed dilute HNO3 only insitu from KNO3 and H2SO4. The start is violent but nothing unmanageable with a bucket of ice water as the first little bit of EtOH was added. Don't know how safely it could be scaled due to the large amount of heat and NOx generated in this synthesis. Perhaps outside in a snowbank you could bucket chemistry it but thats still to be seen.

However it is indeed large amount of AcOH but I have yet to work it up out of fear. After seeing reports of Nitric acid and AcOH exploading with heat im kind of reluctant to distill it for obvious reasons so its been sitting there bottled up buried up to its neck in sand because I dont know what the hell to do with it right now and I fear it could go off. I doubt it would spontanously but im not a big fan of "what ifs".

I also do not think what I made is glacial either since it has shown no signs of being so. I got side tracked right after performing the synthesis in reworking the entie layout of my lab to something that resembles a lab almost so its largely been put on hold.

You will find more then likely BTW that if you heat your mixture until NOx is produced it will start to bubble like soda pop and sustain a reaction from that point on. As magpie and the papers provided have shown there is an activation temperature needed before this reaction starts else you need NO2 present already to lower this activation temperature down to almost nothing. What concentration are you speaking of here anyway?

Panache - 23-7-2010 at 17:34

Does anyone have solubility vs temp curves for the systems Acetic Acid/Citric Acid/Sodium Citrate/Sodium Acetate or any combination therefore?

chucknorris - 22-7-2012 at 21:35

I put some 1500ml of vinegar in flask and 500ml of chloroform and then about 50 grams of table salt(to save the 8 grams of chloroform that would be dissolved into every liter of water otherwise) and mixed the contents for 5 minutes and let it sit for a while, then filtered the contents into separator and separated the lower layer and distilled off the chloroform, and about 60ml of acetic stenchy stuff remained. I expect it to be somewhat concentrated acetic acid, still need to test the freezing temp. The salted water that remains, has trace smell of vinegar, so the chloroform does pull it off.

Anyways, does anybody happen to know the solubility of acetic acid into chloroform? I have found out that it can dissolve up to 40-50% of its volume of acetic acid, so counting from this, 500ml chloroform could be used to reform about 6-7 liters of vinegar. Ok, I could test this out by myself since I have some pure reagent grade GAA and chloroform but just if someone has the data already?

Does the acetic acid break down when distilled? The commercial vinegar contains all kind of soluble shit and gunk which would be easy to get rid of by distillation.

[Edited on 23-7-2012 by chucknorris]

[Edited on 23-7-2012 by chucknorris]

ManyInterests - 10-6-2023 at 15:52

I am bumping this thread as a bit of notes on my own first glacial acetic acid synth.

I used 258 grams of sodium acetate (anhydrous) and 390ml of sulfuric acid (at least 95%). I added cold acid to the sodium acetate in the flask gradually and left everything to cool before heating it on the mantle. It originally took a while for anything to come over, as this was my first attempt at glacial acetic acid and my setup currently has no temperature control, I was afraid that I was distilling sulfuric acid over as it took a while for anything to come over. I did get a yield of 150ml (out of an expected 210ml) and I stopped.

I realized I was a touch too hasty as the flask stank of acetic acid when I removed the distillation joints. At any rate for a first attempt it was very good. I had a specific gravity of 1.0564. So not 99% for sure, but certainly close.

I added it all to around 30 grams of anhydrous MgSO4 in a flask and I will distill that over shortly.

ManyInterests - 12-6-2023 at 17:00

I did a 2nd distillation and there was no discernable drop in SG. I am still at the exact same thing that happened before. I guess I should have better luck next time, but for now it is good enough.

Fery - 12-6-2023 at 19:49

You can also try to approximate its purity by its freezing / melting point. It tends to produce supersaturated solution in fridge at +4 C, but on shaking it suddenly starts to crystallize then. Leaving it in fridge for long enough time, the small temperature oscillations cause the crystals to regrow in the bottom (higher density) and the liquid to move upwards (lower density) so you can remove more liquid (diluted acid) as less liquid stays trapped inside solid phase. Solid phase has higher density and thus lower volume so no glass flask cracking unlike when freezing water where solid phase has lower density and expands in volume.

chornedsnorkack - 12-6-2023 at 22:48

Quote: Originally posted by Fery

You can also try to approximate its purity by its freezing / melting point. It tends to produce supersaturated solution in fridge at +4 C, but on shaking it suddenly starts to crystallize then. Leaving it in fridge for long enough time, the small temperature oscillations cause the crystals to regrow in the bottom (higher density) and the liquid to move upwards (lower density) so you can remove more liquid (diluted acid) as less liquid stays trapped inside solid phase. Solid phase has higher density and thus lower volume so no glass flask cracking unlike when freezing water where solid phase has lower density and expands in volume.

Now the question is crystal size/cleanliness.
Acetic acid and water make a simple eutectic at -27 C and 60% acetic acid by weight. This means that while concentrated acetic acid is hard to resolve by distillation (it is not actually an azeotrope, but it is a near-azeotrope, so the vapour composition is nearly the same as liquid), it should give a neat solid in terms of crystals - solid acetic acid.
Now the question is, does the glacial acetic acid separate as neat big crystals easily cleaned of mother liquor, or fine slush hard to separate?

Tsjerk - 13-6-2023 at 00:10

When 98-99% acetic acid freezes it forms a mesh from which more dilute acid melts when it is allowed to heat up a bit. When you for example freeze at 4 degrees, and slowly thaw at 10, while keeping the bottle upside down, you will get block of porous acetic acid very close to 100%.

Fery - 13-6-2023 at 06:30

I let glass bottles with commercial 98% acetic acid in a fridge for few months. The temperature oscillations around +4 C made the liquid formerly trapped among crystals to slowly raise upwards (hundreds of partial melting and freezing steps) so finally there was a block of solid mass and a little of liquid on top (that could be still something like 90% acid, it can be found in tables which concentration freezes/melts at +4 C).
If you do not have so much time, the method posted by Tsjerk is faster.

Tsjerk - 13-6-2023 at 08:29

I have to add my acetic acid was also frozen over many freeze/thaw cycles; in my shed over winter. Probably between 0 and 10 for months.

ManyInterests - 27-6-2023 at 22:19

I never tried to freeze it. But I am not sure if my freezer on max settings can make something go as cold as -27C.

Maybe I did end up making glacial acetic acid and not aware of it. One thing I wonder is that even if it is at 95%, can I still use it to make acetic anhydride using the calcium chloride/sodium acetate + sulfuric acid route (I post a link to it on the acetic anhydride sticky).