Sciencemadness Discussion Board

purifying acetic acid

chemrox - 12-2-2007 at 00:19

My glacial acetic acid isn't 'glacial' anymore. I'd like to remove the traces of water and can't find my copy of Purification of Laboratory Chemicals. I am thinking of adding a small amount of sulfuric and then distilling the acetic from the mixture using a drying tube on the vacuum adapter.

joeflsts - 12-2-2007 at 05:26

Quote:
Originally posted by chemrox
My glacial acetic acid isn't 'glacial' anymore. I'd like to remove the traces of water and can't find my copy of Purification of Laboratory Chemicals. I am thinking of adding a small amount of sulfuric and then distilling the acetic from the mixture using a drying tube on the vacuum adapter.


I have read that trying to distill GAA with Sulfuric can be quite troublesome. I haven't tried it myself.

Joe

Maya - 12-2-2007 at 06:53

Add some acetic anhydride to react with the water

SecretSquirrel - 12-2-2007 at 07:09

How about azeotropic distillation (with benzene or toluene)? I don't know if you have the resources, but it is another possibility.

unionised - 12-2-2007 at 11:15

I have a feeling there might be a brief reference to this matter elsewhere on this site. Ah! yes here's 6 pages or so.
https://sciencemadness.org/talk/viewthread.php?tid=2194

I would say UTFSE, but, to be fair I have never found it to work very well. Google and site:.sciencemadness.org works quite well.

chemrox - 12-2-2007 at 16:57

UTFSE? I'm still trying to find out what IIRC means....

GhostofUnintentionalChaos - 12-2-2007 at 17:06

UTFSE: use the fucking search engine. I also have no clue what IIRC means, however.

acetic acid purification-unexpected precipitation

chemrox - 12-2-2007 at 17:09

I checked the old thread and nobody seemed to have had a clue then either.

I placed 250 ml in a flask, added 33 ml con H2SO4 and distilled with simple ditillation appratus into a flask with a CaCl2 drying tube. The liquid boiled from 118 degC and I collected about 200 ml between 118 - 128 deg C. Odd thing was a white precipitate formed in the condenser. Washed it out with acetone/CH2Cl2. Suspect acetate but wonder why. Will know more soon.

bereal511 - 12-2-2007 at 17:14

Off topic, IIRC means "if I recall correctly" or "if I remember correctly. IIRC.

leu - 12-2-2007 at 20:22

Sulfuric acid cannot be used to dehydrate acetic acid, it's used industrially to prepare glacial acetic acid by codistllation with sodium acetate. The entry from Purification of Laboratory Chemicals:

Acetic acid (glacial) [64-19-71 M 60.1, m 16.6O, b 1180, d 1.849, n 1.37171, n25 1.36995, pK 4.76. Usual impurities are traces of acetaldehyde and other oxidisable substances and water. (Glacial acetic acid is very hygroscopic. The presence of 0.1% water lowers its m by 0.2O.) Purified by adding some acetic anhydride to react with water present, heating for lh to just below boiling in the presence of 2g CrO3 per l00 mL and then fractionally distilling [Orton and Bradfield J Chem SOC 960 1924,983 1927. Instead of CrO3, 2.5% (w/w) of KMn04, with boiling under reflux for 2-6h, has been used.
Traces of water have been removed by refluxing with tetraacetyl diborate (prepared by warming 1 part of boric
acid with 5 parts (w/w) of acetic anhydride at 600, cooling, and filtering off), followed by distn [Eichelberger and La Mer
J Am Chem Soc 55 3633 1933].

Refluxing with acetic anhydride in the presence of 0.2g % of 2-naphthalenesulfonic acid as catalyst has also been
used [Orton and Bradfield J Chem Soc 983 1927]. Other suitable drying agents include CuSO4 and chromium triacetate: P2O5 converts some acetic acid to the anhydride. Azeotropic removal of water by distn with thiophene-free *benzene or with butyl acetate has been used [Birdwhistell and Griswold J Am Chem Soc 77 873 1953]. An alternative purification uses fractional freezing.
Rapid procedure: Add 5% acetic anhydride, and 2% of CrO3. Reflux and fractionally distil.

There are several other threads in which this topic is covered in which more information has been provided, these threads can be found by anyone with enough patience to keep looking until they're found :P One shouldn't indulge in dismissing other's posts when one is looking for information, unless one wishes to be ignored. The use of charcoal was the subject of Farmatsiya 9 No. 2, 39 (1946). Anhydrous copper sulfate is probably the easiest to obtain desicant, though other good methods are described in the patents already posted :D

[Edited on 13-2-2007 by leu]

solo - 12-2-2007 at 21:40

Reference Information

Purification of Laboratory Chemicals


http://www.4shared.com/dir/1625516/d79e37e7/sharing.html

chemrox - 12-2-2007 at 23:29

Thanks especially for the texts..I will use aceticanhydride KMnO4 next time.

I am baffled by the precipitate. I have it in solvent and will isolate it tomorrow and try to see what it is. Could I have leached enough Ca from the drying tube to make CaAcetate. (I'm affraid of using abreviations anymore lest i get harshly flamed again one of the great beacons of wisdom and chemical genius that hang around here to admonish us lesser beings.

I really appreciate the posts here.. both for content and friendly spirit.

unionised - 13-2-2007 at 12:49

Chemrox, if you are going to complain about people calling you ignorant you would be better advised not to write stuff like "I checked the old thread and nobody seemed to have had a clue then either." in response to six pages of stuff which (admitedly among other things) answered the question you asked here because you didn't bother to search.

chemrox - 13-2-2007 at 16:37

The new thread had tons of information.. I didn't find much in the old one.

precipitate

chemrox - 13-2-2007 at 16:49

So I used H2SO4 to 'dry' the acetic and wish I'd had "Purification of Laboratory Chemicals" at the time. I noted a "white precipitate.." almost clogging my condenser. Actually the "precipitate" was frozen acetic ...solidifies 16.7. What through me was the receiving flask felt like it was about 25 deg. What I didn't consider was cold spots on the condenser walls. Next time I shall ice the receiving flask and let the water in the condenser be a bit warmer.

Overall this has been an embarassing week and I think I'll retire for awhile.

unionised - 14-2-2007 at 12:15

" I didn't find much in the old one. "
Well, I'm puzzled. that thread mentions distillation, freezing, conversion via Ca and Na acetates and a few other things. The freezing option is the one I'd use at the moment. Put the bottle outside overnight then pour off the liquid in the morning- glacial acetic acid gets left behind.
If the weather was warm I'd distill the stuff. Can't see a good reason for adding H2SO4.