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Alastair
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Drying acetic acid
So i have some 70 per cent acetic acid and i was hoping to dry it (now what i really dont get and even wikipedia didnt help my dumb brain on this is
acetic anhydride. It is crystals right? and anhydrous acid is? just staggers me...and why the hell use AcOH as a name?  )
Anyway, i was making some apple pie and on that occasion dried some MgSO4 in oven (not sure about perfectly anhydrous but it became white and i
covered immediately after removing from heat).
I tried absorbing water with the powder but it didnt go well, i got a white solution.
Adding it to AcOH did nothing obvious.
What i did later was disolve it in some water (some crystals did absorb H2O but it was mainly a whitish somewhat oversaturated solution). Then i added
it to 70% AcOH. This was done on very small scale but in a matter of minutes i noticed some ''glaciers'' floating on top of solution, while white
residue was on the bottom. I think if done on larger scale it may become an easy and very ghetto method for glacial acetic acid.
By the way, if i add minor quantities or water to disolve the floating crystals it wont be anhydrous acetic acid, right? im having real problems with
its concept 
[Edited on 10-11-2011 by Alastair] Typos.
[Edited on 10-11-2011 by Alastair]
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Adas
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AFAIK, glacial acetic acid freezes around 17°C. Maybe you haven't dried your MgSO4 very well. Try to heat it over 150°C.
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Neil
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http://www.sciencemadness.org/talk/viewthread.php?tid=9
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ScienceSquirrel
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Drying 70% acetic acid is going to be really hard as there is so much water in it. Most drying agents and methods are meant to deal with a few per
cent of water at most. 70% acetic acid contains just over sixteen and a half moles of water per litre, in molar terms it is more water than acid!
I would suggest something drastic like distilling it from concentrated sulphuric acid which is cheap and readily available and loves water.
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Chemistry Alchemist
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On my blog page ive got a list of chemicals and there drying agent, you can check it out... pretty sure acetic acid is one of those chemicals
toothpick93.blogspot.com
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bahamuth
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Anhydrous copper sulfate is a excellent drying agent for acetic acid, though with the amounts of water you have you would need alot of it, and the
copper sulfate is really hard to dehydrate, loosing the last water molecule at around 200 degrees Celsius, though in my own experience the copper
sulfate does not turn completly white/grey white (indicating anhydrous state) before around 300 degrees C. and several hours at those temps.
Any sufficiently advanced technology is indistinguishable from magic.
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Bot0nist
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I agree about the copper sulfate. It is kinda a bitch to dry.
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Sedit
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Dilute with DCM and add MgSO4, Filter, after that distill off the DCM to recover crystals of Glacial Acetic acid.
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"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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DJF90
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You wont have crystals of GAA unless the temperature is low enough. More likely, the GAA will be a liquid after distillation of the DCM. You might
want to fractionally distil your product to ensure purity...
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bahamuth
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I propose that instead of using multi-solvent approaches, dry it with a high water capacity drying agent like anhydrous MgSO4 (might even work with
silica gel), distill it and dry it with anhydrous copper sulfate, giving less than 0.01% water IIRC if done properly. All substances are reusable
ensuring cheapest route. If DCM or any other solvent is used one might just buy GAA analytical grade as it is dirt cheap, or even industrial
grade/food grade in 25L plastic drums, which even here in Norway is as cheap as 175-200 USD and no restrictions on.
Any sufficiently advanced technology is indistinguishable from magic.
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Alastair
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Well im not in US or Norway sadly. Thank you all for great support and help! But what could the crystals have been then? Im sure there was only dH2O
and acetic acid with pure MgSo4. Oh, maybe because i did it in a metal container (not aluminium but idk what metal)?
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bahamuth
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As I see it, but can not be certain, your solution of MgSO4 in water, added to your 70 % acetic acid did precipitate MgSO4 upon mixing the two
solutions leaving you with "glaciers" and white precipitate in the bottom of your tube.
Acetic acid is way to miscible with water to be able to salt anhydrous(100%)/glacial(97-100%) acetic acid out of the water with MgSO4 or any salt that
I know of...
As per your questions about the state the compounds, glacial acetic acid and acetic anhydride. Glacial acetic acid freezes around 16-17 degrees
Celsius, giving rise to the name "glacial" acetic acid. Acetic anhydride freezes at -73 degrees Celsius. Those are two different compounds if there
was any doubt. AcOH is not a name for acetic acid, it's an abbreviation. The common abbreviation for acetic anhydride is Ac2O.
Hope this helps.
Damn, had to edit spelling twice, to late need to sleep..
[Edited on 12-11-2011 by bahamuth]
[Edited on 12-11-2011 by bahamuth]
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White Yeti
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I agree with bahamuth, acetic anhydride and glacial acetic acid are NOT the same thing. One is used to make esters and the other is a highly regulated
chemical used to make heroin O.o
Acids exists as "anhydrides", but be careful because following this logic, SO3 is the "anhydride" of sulfuric acid, CO2 is the anhydride of carbonic
acid and NO2 is the anhydride of nitric acid etc....
Acetic anhydride is the anhydride of acetic acid because it can be hydrolysed into acetic acid.
Hope this helped.
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Lambda-Eyde
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Quote: Originally posted by White Yeti  | | I agree with bahamuth, acetic anhydride and glacial acetic acid are NOT the same thing. One is used to make esters and the other is a highly regulated
chemical used to make heroin O.o |
Both are used for making esters, it's just that acetic anhydride does the job much better in most cases. That's why it's used in production of heroin
(diacetylmorphine).
| Quote: Originally posted by White Yeti | Acids exists as "anhydrides", but be careful because following this logic, SO3 is the "anhydride" of sulfuric acid, CO2 is the anhydride of carbonic
acid and NO2 is the anhydride of nitric acid etc....
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No, dinitrogen pentoxide, N<sub>2</sub>O<sub>5</sub>, is the anhydride of nitric acid.
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White Yeti
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I apologise for mixing up a few facts, I was trying to make a point, not to supply the OP with all the information about acids and their anhydrides.
Acetic acid is used for many different things, making esters is the only one that came to mind at the time.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Sedit
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Glacial acetic acid is a dimmer not an anhydride.
I have found the DCM method the only way to get glacial acetic acid because MgSO4 starts to loose water when you heat it and that comes over when you
distill. Dilute with DCM and it becomes a walk in the park and ensures you don't lose much AcOH when adding the drying agent.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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bahamuth
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Well one way to avoid that the magnesium sulfate loses water on heating is to remove it before heating by filtering/decanting etc. This is what i
commonly do, and if I want to distill a dried solvent over a desiccant of sorts, I make sure that it will keep its water at distilling temp. One way
is to add as much desiccating salt that only the first water of hydration is allowed to exist, thus preventing loss of it on heating to distilling
temps.
Copper sulfate loses its last water of hydration at atleast 200 degrees Celsius, way more than enough to distill acetic acid.
Think stoichiometry is the key to sucess.
Any sufficiently advanced technology is indistinguishable from magic.
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Alastair
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| Quote: Originally posted by bahamuth | AcOH is not a name for acetic acid, it's an abbreviation. The common abbreviation for acetic anhydride is Ac2O.
Hope this helps.
This explained everything thank you.
Information given is awesome (and im not making heroin, get real). Do you guys know about the azeotrope of water and AcOH? |
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Sedit
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| Quote: Originally posted by bahamuth | | Well one way to avoid that the magnesium sulfate loses water on heating is to remove it before heating by filtering/decanting etc.
|
The fact that he's starting with 70% AcOH means a relatively large amount of MgSO4 will need to be used and much loss will be had hence the reason why
I suggested diluting with DCM. It distills quickly and cleanly. Also as an added bonus he should have two layers at the start so he will know that the
drying agent is having effect as the water water later goes away.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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bahamuth
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Don't they have search engines in Bat Country?
This is such a common problem that using goggle will give you a couple good hits on "acetic acid water azeotrope" or the similar.
Me, I found azeotrope data on wiki, and discovered there is no azeotrope between the two compounds in question, but rather a zeotrope. Wiki Link
And since "we" now know about the azeotropic nature of acetic acid:water, what did you really want to know, specificity is the key to proper
spoonfeeding
PS. If you are going to quote keep it proper, as half your quote in your last post is mine and half is your own post.
PSS. | Quote: Originally posted by Sedit | | Quote: Originally posted by bahamuth | | Well one way to avoid that the magnesium sulfate loses water on heating is to remove it before heating by filtering/decanting etc.
|
The fact that he's starting with 70% AcOH means a relatively large amount of MgSO4 will need to be used and much loss will be had hence the reason why
I suggested diluting with DCM. It distills quickly and cleanly. Also as an added bonus he should have two layers at the start so he will know that the
drying agent is having effect as the water water later goes away. |
I've never tried the DCM route, though I agree it sounds quite easy if you have small amounts of acid to dry (separating funnel size depending..?).
But for someone that isn't able find in the litterature the drying agents and reasoning which ones he could/should use might not have DCM at hand.
Me myself has always used textbook drying agents and they usually work quite well.
Guess that the total volume of the 70 % acetic acid:water solution he wants to purify is something to consider when he decides on the approach.
Any sufficiently advanced technology is indistinguishable from magic.
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Alastair
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Hey bahamuth, thanks for being a buttock, i hope it feels good to have been born knowing every goddamn thing on earth and being so much smarter than
everybody. If i am offended by a question i dont answer it. Unless it makes you happy to speculate how smart somebody is and dramatize over
spoonfeeding, just ignore my posts, thank you.
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Panache
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dcm by itself azeotropes about one percent water with it. I think that's why sedits solution is so effective. By itself the mag sulphate is not known
to effectively dry AA, however by diluting into dcm removing most of the water with mgso4, then distilling the dcm this removes the final portion of
water leaving you with dry enough AA to crystallise readily in a cool place.
Having produced dry AA from vinegar by going down the acetate route I known how difficult aa is to dry. I would listen to sedit, dcm is generally
widely available, easily distillable from a warm water bath using any old polyolefin vessel (read plastic bucket with snap on lid) and non flammable.
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kmno4
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I am going to try this "DCM methode", because it looks very unusually - I do not think if it works at all.
But experiment is king.
First - I have to prepare 70% sol. from my pure acetic acid....
We will see 
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Panache
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| Quote: Originally posted by kmno4 | I am going to try this "DCM methode", because it looks very unusually - I do not think if it works at all.
But experiment is king.
First - I have to prepare 70% sol. from my pure acetic acid....
We will see |
Me too!
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Sedit
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Why does it seem odd?
The DCM is just a low boiling point solvent to minimize loss when adding the bulky drying agent. Im sure other solvents can be used as well but DCM is
ideal for its rapid removal.
[Edit]
Water does not mix with DCM and yet AcOH does... Look at the other thread for salting out AcOH where I performed many experiments on the synthesis and
extraction of AcOH. Its easy.
[Edited on 20-11-2011 by Sedit]
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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