Concentrating Acetic Acid

[10fingers]

I have some dilute acetic acid that I want to concentrate into glacial acetic acid, it's about 70%. I have tried mixing it with H2SO4 and distilling it but it doesn't work very well. It seems that when these two acids are mixed together it significantly raises the boiling point and the acetic acid doesn't want to distill out. Also it starts bumping badly. Even using a vacuum doesn't help. I am also thinking that the higher temp required may be causing the acetic acid to partially breakdown giving some water which dilutes any acetic acid in the receiving flask.
I was thinking of using a fractionating column setup with just the acetic acid. Does anyone think this will work?

<small>[ February 11, 2003, 12:53 AM: Message edited by: 10fingers ]</small>

[Mr Cool]

I think fractional distilation might work. If you can get it up to about 90% then you could finish it off in a dessicator.

[mongo blongo]

I don't know if this has been suggested before but what about mixing it with a desiccant and filtering?

[Al Koholic]

Well...assuming the dilute acetic acid in question is vinegar, you'd need a load of dessicant thats for sure. This could be another method once it is up to 90% or so concentration.

I've got some plans to attempt a concentration of acetic acid myself. Glacial acetic acid is useful in a lot of syntheses and is just good to have around. It's boiling point is 118C so it should work by fractional distillation with careful temp control and a vigreux column to aid in separation. At least thats what I plan on doing....

[vulture]

I currently have a longterm experiment running where I'm trying to dessicate 80% acetic acid with an excess of anhydrous magnesium sulfate. I haven't checked on it recently and I can only check it in the weekends that I'm at home, so you'll have to wait...

[a_bab]

What about trying to freeze it ? If I remember correctly, the freezing point is about 15 degrees for 98% acetic acid. Maybe you'll be able to get crystals somewhere near 0 degrees celcius.

[IPN]

And one way is to make sodium acetate (mix sodium bicarbonate and acetic acid) and distill that with H2SO4 to get glacial acetic acid.

<a href="http://roguesci.org/megalomania/synth/synthesis1.html#acetic" target="_blank">http://roguesci.org/megalomania/synth/synthesis1.html#acetic</a>
Here you can find the whole procedure.

[VX]

If you have some strong oxidiser (potassium permanganate, potassium dichromate etc) it might be easier for you to simply oxidise plain old denatured alcohol (preferably after distilling a little bit of it to remove methanol) into acetic acid. This would give pure acid, which can be distilled off once the reaction is complete.

A point to keep in mind however is that the reaction proceeds via ethanal (acetaldehyde) which has a lower boiling point than both the alcohol and the acid. It is necessary to use refluxing conditions to prevent the aldehyde evaporating before any acid is produced.

[Einsteinium]

Glacial acetic acid is avaible for cheap at photographic supply stores (Kodak brand rulez <img border="0" title="" alt="[Wink]" src="wink.gif" /> ) and is the usual way to go with this stuff. You can concentrate it since it produces an azeotrope with water boiling @ 76,6C of composition 97%/03% Acetic Acid/Water. This can then be refluxed over anhydrous CaCl₂ or MgSO₄ for an hour or so to yield almost anhydrous acid. Another trick would be to boil an azeotrope with water first (example : benzene/water boils @ 69,4C) and then, when all water has been distilled out, only GAA would remains in the flask (which can be distilled @ 118,1C). Honestly the Kodak way is easier and the product if of higher purity, you should stick with it :p

[10fingers]

Thanks Einsteinium, that's useful info. I have tried to find GAA at photographic suppliers but no luck so far. When they list there chemicals they use names like developer, fixer, stop bath, etc. I don't know what the ingredients of these things are. If a supplier had GAA is that what you ask for or does it go by another name?
The acetic acid I have now I made from sodium acetate and sulfuric acid. I tried refluxing it with anhydrous magnesium sulfate for several hours but still it was not glacial. I check it afterwards by putting it in the fridge but it doesn't freeze. By measuring density, I have found that the concentration I can get is around 80%. No matter how I try to distill it, reflux it, or use drying agents, it never gets any higher.
Another question concerning making acetic acid, when I combine a stoichiometric amount of sodium acetate and conc. sulfuric acid into a flask there is an immediate reaction. It gets pretty hot and gives off strong acetic acid fumes. For some reason though not all of the sodium acetate reacts, it seems like there needs to be much more H2SO4 added to the reaction.
Another thing, I was wondering if there were any side reactions which produce something which is hard to remove from the acetic acid. It may be the reason that I can't get GAA is that there is something else in it besides water which can't be distilled out. Anyway, this is pissing me off, it shouldn't be this much trouble to make GAA.

[blazter]

Has anyone considered trying to extract an acetic acid source, like vinegar with a nonpolar solvent. The merck index says that GAA is miscible with ether, so would it be possible to just extract the acetic acid that way? Since GAA has a BP of like 110C and ether boils around 30C the separation should be easy assuming that it works.

[Einsteinium]

10fingers: Neutralizing sodium acetate with sulfuric acid should be done smoothly to limit side reactions that may happen since it heats up a lot. Are you certain of the concentratrion/purity of your acid and acetate? Do you use a simple distilliation settings or fractionnal?, you would definitivly have a better result from fractionnal distillation here. I know GAA is used in photography for some baths, can't tell which one, but a web search should give you the answer.

blatzer: Acetic acid is very polar and miscible in any concentration with water. Somewhat soluble in any non-polar solvents, like diethyl ether, but still you will need to extract your vinegar with more than 10x it's volume of ether and still you will be left with only a few GAA extracted.