Sciencemadness Discussion Board

Glacial acetic acid from acetic anhydride?

LD5050 - 5-7-2017 at 19:15

I'm looking to make some GAA. So far I have read about sodium acetate and H2SO4 method but I read that it necessarily doesn't give GAA but rather highly concentrated acetic acid. I don't really want to use my precious AA but I am wondering if this could easy be done by maybe just adding a bit of H2O?

[Edited on 7-6-2017 by LD5050]

Loptr - 5-7-2017 at 19:50

Glacial acetic acid is concentrated acetic acid.

I am sure some here would jump you if you attempted to make acetic acid from the anhydride. :o

I will trade you my glacial acetic acid for your acetic anhydride. Deal? :cool:

[Edited on 6-7-2017 by Loptr]

JJay - 6-7-2017 at 00:20

I think you can remove more of the water by distilling it from more sulfuric acid (Edit: I'm assuming that you start with an equimolar amount of sulfuric acid). I have read a couple of threads suggesting that it can be dehydrated with copper sulfate (which can be re-used), and supposedly even magnesium sulfate works.

You'd probably want to start with highly concentrated acetic acid and purify it by adding acetic anhydride rather than putting acetic anhydride into water.

[Edited on 6-7-2017 by JJay]

Melgar - 6-7-2017 at 07:03

Yeah, if you really want to make it, use the acetic anhydride to get the last few percent of water out of the concentrated stuff. But it's cheap enough, and if you're in the US, you can just get it from Duda Diesel like we all do:

https://www.dudadiesel.com/search.php?query=acetic

woelen - 6-7-2017 at 07:15

I have actually done this to make really water-free acetic acid. I had 250 ml of acetic acid, which was sold to me as "at least 99%" acetic acid, the remainder being water. To this, I added 3 ml or so of acetic anhydride and put it away for a night. After that, all water has reacted and you have truly anhydrous acid. I now most likely have a few tenths of percent of acetic anhydride in the acid as impurity, but for my specific experiments this is less severe than having a percent of water.

Using acetic anhydride for this purpose is not a waste of this precious chemical, you only need a very small amount of this for making a large amount of acetic acid really anhydrous. Using acetic anhydride for making acetic acid by adding the right amount of water indeed is a waste. Then buy acetic acid at whatever place you can get it, at the highest concentration and then if necessary add just a few ml of acetic anhydride to make it truly anhydrous.

LD5050 - 6-7-2017 at 08:20

The reason for asking this was because I needed GAA and I didn't want to wait the two weeks for delivery. Would it be possible to make sodium acetate from vinigar drying this in the oven then distilling over H2SO4 and then adding a few ml of acetic anhydride? Or should I distill sodium acetate over H2SO4 once then again and then add a drying agent like melecular sieves or something else?

JJay - 6-7-2017 at 09:09

Molecular sieves are attacked by acetic acid and should not be used to dry it. Suitable drying agents are sulfuric acid, anhydrous copper sulfate, and perhaps magnesium sulfate (idk).

I don't really know how dry your sulfuric acid is/how dry you can get your sodium acetate/how valuable your time and acetic anhydride are/how much GAA you need/etc. Only you can decide whether to use a drying agent before adding acetic anhydride.

woelen - 6-7-2017 at 12:37

If you are doing this for a hobby, then simply wait two weeks for your glacial acetic acid and then add 1% of volume of acetic anhydride to make it really anhydrous. Easiest and cheapest. Hobby activities should not be in a hurry ;)

DraconicAcid - 6-7-2017 at 12:45

Can you purify acetic acid by freezing it? If you have concentrated acetic acid, well-chilled, surely the crystals formed will be pure acetic acid?

Melgar - 6-7-2017 at 13:55

Quote: Originally posted by woelen  
If you are doing this for a hobby, then simply wait two weeks for your glacial acetic acid and then add 1% of volume of acetic anhydride to make it really anhydrous. Easiest and cheapest. Hobby activities should not be in a hurry ;)

Agreed. After a day of waiting, you'll think of some other experiments to do in the meantime, and then when the acetic acid arrives, it'll be a pleasant surprise. :)

Sedit - 7-7-2017 at 07:36

Add DCM to your acetic acid as well as a drying agent like MgSO4, Filter and distill off the DCM and you will be left with GAA.

I don't even distill H2SO4 and Sodium Acetate, I just add a shitload of DCM, Filter it and add a drying agent because i found there to be less loss then with distilling the mixture which tends to heat unevenly.

[Edited on 7-7-2017 by Sedit]