HgDinis25 - 20-12-2014 at 16:28
Vinegar is widely available to the home chemist. However, it's usually a very dilute solution of Acetic Acid (5%) and it has a lot of crap in it.
There aren't many proposed methods to purify and concentrate the stuff, and the ones available are difficult and time spenders.
Because of this, I spent some time thinking about a good way to obtain decent conentrations of Acetic Acid from vinegar. The method that I come up
with uses a Dean-Stark distillation.
Note: one should always start with White Vinegar because it's usually the less contaminated Vinegar. Other kinds of Vinegar might
also work.
Theory 1: Toluene and Water form an azeotrope consisting of roughly 80% Toluene and 20% Water; it has a b.p. of 84,1ºC. It doesn't
form an azeotrope with Acetic Acid neither do the three of them form a ternary azeotrope.
Source: http://en.wikipedia.org/wiki/Azeotrope_%28data%29
Theory 2: In a Dean-Stark Distillation, water is distilled as an azeotrope (usually with Toluene) and is then drained while the
Toluene is allowed to return to the reaction vessel.
Here is a simple image that more or less describes this type of distillation: http://what-when-how.com/wp-content/uploads/2011/06/tmp17011...
And here is an improvised version, built with common ground glass joints (Dean-Stark traps are expnsive and many hobbists don't have them): http://www.erowid.org/archive/rhodium/chemistry/equipment/pi...
Theory 3: Acetic Acid is miscible with Toluene.
http://www.perfinity.com/downloads/Solvent%20Miscibility%20a...
So the procedure I propose is the following:
1-Add the Vinegar to a RBF and add Toluene to it. Set up your improvised (or not) Dean-Stark distillation apparatus;
2-Start heating up. The azeotrope should boil at 80ºC, almost 40ºC away from Acetic Acid's b.p. (wich is 118ºC);
3-The distillate should start to collect in the trap. Draining the water in the trap is necessary from time to time.
Now it's where things start to get interesting. Toluene is miscible with Acetic Acid. If all water is distilled out one would get a solution of
Toluene in Acetic Acid. I can't think of an easy way to seperate the two of them. Perhaps stopping the distillation when Acetic Acid concentration in
water reaches ~80%? I would presume there would be two layers (the Acetic Acid one and the Toluene one), easy to seperate. After seperating the two, a
final distillation should me done to seperate the Acetic Acid from solid contaminants the vinegar had.
I haven't tried this yeat because I lack 2 pieces of quickfit glassware to make the Dean-Stark apparatus.
So what do you think? Too elaborated and "mad" just to get some Acetic Acid from vinegar?
Metacelsus - 20-12-2014 at 16:49
Acetic acid may be miscible with toluene, but it is also miscible with water. I'm not sure your proposed method will work very well, as there might be
a ternary azeotrope.
Why not distill off the water normally?
Take a look at this paper; your method is possible, but complicated.
http://www.bvucoepune.edu.in/pdf%27s/Research%20and%20Public...
[Edited on 21-12-2014 by Cheddite Cheese]
Sedit - 20-12-2014 at 18:09
Could one just add a mess load of Anhydrous Magnesium Sulfate to a heated mixture like this and let the Magnesium cool and crystalize. I know it would
take alot but its cheep and reusable.
diddi - 20-12-2014 at 19:11
not sure if this would work, but it would avoid an azeotropic distillation:
Convert CH3COOH to CH3COONa and extract as hydrated solid from supersaturated sln
heat to reliquefy and displace Na+ with HCl
Mesa - 20-12-2014 at 19:13
I believe there is a similar method used commercially employing ethyl acetate/water/acetic acid.
HgDinis25 - 21-12-2014 at 04:46
@Cheddite Cheese
Wikipedia doesn't list a ternary azeotrope for the three of them. Even if it exists, the Acetic Acid loss in the water removed in the trap might be
quite small. Haven't read the paper you mentioned yet though.
@Sedit
What do you mean by "a mixture like this"? I supose it is also a good method. Once could add a large quantity of Anhydrous Magnesium Sulfate to
Vinegar and then star distillating the Glacial Acetic Acid (if formed). The Acetic Acid would boil around 118ºC, while the Magnesium Sulfate
Heptahydrate would only dehydrate at 150ºC.
@diddi
Usually that's the route used to get Glacial Acetic Acid. First distill it to get clean Vinegar, then react it with a base (usually NaOH). Boil out
the water and dehydrate the salt. React the resulting compound with Sulfuric Acid to get glacial acetic acid. You can use HCl, at the cost of
concentration of Acetic Acid. The method I proposed was suposed to avoid this, by only using toluene to displace all the water from the solution.
Anyone with the equipment needed care to try this out?
Texium - 22-12-2014 at 08:59
Well, this is merely speculation, but couldn't you carry it out simply using two distillations, one to first remove dissolved contaminants from the
vinegar, and a second one to remove the water, possibly with the aid of a fractioning column?
I don't know if that would be practical, but it avoids introducing any other potential contaminants that would need to be removed.
unionised - 22-12-2014 at 09:12
http://www.sciencemadness.org/talk/viewthread.php?tid=23404#...
and a stack of similar threads already discuss this sort of thing.
Did nobody remember to think about searching?
[Edited on 22-12-14 by unionised]
HgDinis25 - 22-12-2014 at 13:08
@zts16
The topic unionised referes to adresses that question.
@unionised
A stack of similar threads did discuss how to concentate vinegar. But non of them through this method. And because there were at least 4 that I saw, I
decided to create a new one for a Dean-Stark type distillation method. Of course I could have added this to an old topic, I just didn't know if it
woud fit in, as there are a few of them. Moderators can obviously merge it if they think a new topic on the matter isn't appropriate. I apologize in
advace, if this is such a case. Maybe you can add some constructive knowledge to the discussion? I know you're filled with it...
To answer your question, somebody did remember to search it. Actualy, I can tell you a lot of wa... Oh wait... Was that a rhetorical, sarcastic,
uncalled-for question? Like this one I've just written?
diddi - 22-12-2014 at 14:38
"Who drank my mercury?" 
unionised - 23-12-2014 at 05:42
re."
1-Add the Vinegar to a RBF and add Toluene to it. Set up your improvised (or not) Dean-Stark distillation apparatus;
2-Start heating up. The azeotrope should boil at 80ºC, almost 40ºC away from Acetic Acid's b.p. (wich is 118ºC);
3-The distillate should start to collect in the trap. Draining the water in the trap is necessary from time to time."
At the boiling point of the toluene/water azeotrope (near 80C) the vapour pressure of acetic acid is about 200 mmHg
http://en.wikipedia.org/wiki/Acetic_acid_%28data_page%29
so the vapour will also carry a fair bit of the acid with it.
You will slowly but steadily throw it away at stage 3 if you are not careful (or unlucky).
Also, as was already pointed out, the acid is soluble in water as well as toluene.
I can't find data for the partition coefficient for acetic acid between water and toluene, but there's data for crude oil which suggests that most of
the acid would dissolve in the water, rather than the toluene.
You would almost certainly be better off with a fractionating column.
However, there are much better ways to get acetic acid from vinegar.
And starting a new thread so that anyone subsequently looking for information will now have one more thread to trawl through doesn't seem very
helpful.
Templar - 24-12-2014 at 14:51
I would assume the acetic acid would have a greater affinity for water than toluene... maybe using DCM to extract it would be a good idea.
Honestly though, make sure you can't get 90%+ acetic acid locally. All the cleaning places carry it, it isn't watched here.
Formic acid can also replace it in some applications ; al/hg, henry condensation, etc
HgDinis25 - 25-12-2014 at 04:49
Well, thank you all for your input. I'll try this procedure as soon as I have the equipment needed (hahaha it's Christmas so I'll have it soon ). I'll report back with the results.
@diddi
Was it you? Watch out if you go for a swim, you are going to sink like a nail...
@unionised
Thanks for the data. I'll look into it.