Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Seperation of AcOH and Ac2O
Let me toss this out to the forum in general.
Suppose we have a relatively large amount of AcOH 9glacial) that is being used as solvent and a relatively small amount of acetic anydride that is our
product. Ac2O boils at 117-118 C and acOH at 140 C so while they could be fractionated, the abundance of the lower boiling solvent would make this
onerous on medium/large scale.
Accordingly I am looking for a good method of extracting the Ac2O from AcOH.
So far I have only found a single solvent that AcOH is essentially insoluble in, that is CS2.
But I have not been able to confirm whether Ac2) is miscible with CS2 or not.
Anyway I would prefer to have other solvent options if possible just because CS2 is so flammable.
Anyone have this info at hand or know where to get it?
I would expect that the protic nature of AcOH would make it sufficiently different from the anyhydride.
Ideas?
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Canadian Journal of Chemistry Vol 49 # 13 July 1, 1971
From Google's 'view as HTML'
| Quote: | | The acetone - acetic anhydride - carbon disulfide system has been the subject of extended research in this laboratory because the acetic anhydride -
carbon disulfide binary system forms two layers over a composition range of about 35 mol% at 25', the critical solution temperature being 52.8' (1-4),
but the heterogeneity is destroyed by the addition of about 4 mol% acetone. |
http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_abst_e?cjc_v71-357...
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Not as good, as it is a distillation:
Acetic anhydride was purified for measurement of electrical properties by adding toluene and removing the toluene-acetic acid azeotrope with an
efficient column at 100,6 C
Myers, R. T. J. Phys. Chem. 69, 700 (1965)
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Thanks @ n_i. If I read that correctly then CS2 dissolves Ac2O up to 35mol% @25 C. Since CS2 is not miscible with AcOH then it follows that CS2 is a
possible extraction solvent for Ac2O from AcOH preferably by continuous Liq-Liq extraction of appropriate design based on the densities of the three
components.
I think I will request the full article.
So far I have been unable to obtain the two older US patents cited by @S.C.Wack in the acetic anhydride thread.
Given the large abundance of AcOH present the toluene azeotrope would take forever. While a 40 degree C spread is better than a 23 deg C spread, 23
degrees is still sufficient for a good seperation if you have about a 12 tp column and run at a reflux ratio above about 10 - just like the 22 degree
spread in bp between water and ethanol. Slow and tedious but possible.
Anyway this thread is about aviiding distillation entirely.
[Edited on 24-3-2007 by Sauron]
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
No, there's a range spanning a difference of 35 mol-percent in which there are two phases. I'm assuming that at a high percent of either one of the
two compounds you get a single phase of mostly the majority with the small amount of minority compound dissolved in it.
Ice cold water is the only other solvent I could find data on. Given the moderate half life of the anhydride in water it might be possible to
wash the mix with ice water and extract the acetic acid. This could work even better with an additional solvent such as MTBE for the anhydride.
Hydrocarbon solvents might work similar to CS2, as might halocarbons with not too high percentage of halogen compared to carbon. Hector might be able
to do a bit of hands on research at his end.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Thanks for clarification.
CHCl3 and CCl4 are miscible in all proportions with both AcOH and Ac2O. DCM was not mentioned. Pet.ethers were not mentioned. I would think that
sulfolane might be a good candidate also dimethyl sulfone. Worth a look.
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Yeah, the polyhalos seem to be decent solvents for acetic acid. I was thinking of something like the mono-chloropentanes.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Those are possinations. I'm sure there are x-number of solvents that will do this job. Finding them other than by trial and error is the problem.
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
| Quote: | Originally posted by Sauron
Those are possinations. I'm sure there are x-number of solvents that will do this job. Finding them other than by trial and error is the problem.
|
Trial and error may end up the best bet. I've been through two books on lab solvents and one on industrial solvents and haven't seen any more that
what is up here. If I had the materials in question on hand, I could have determined the answers by now.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Unfortunately I have no Ac2O on hand presently and my lab is still down after shifting houses a few months ago. So I can't be of much wet-lab help at
the moment. That's why I was hoping for an answer via peper chase.
|
|
|
Pyridinium
Hazard to Others
Posts: 258
Registered: 18-5-2005
Location: USA
Member Is Offline
Mood: cupric
|
|
I was thinking perhaps a tertiary amine, which in anhydrous HOAc / Ac2O will still act as a Lewis base (though the progressively weaker ones aren't as
good).
The Handbook of Solvent extraction says this can be used to complex acetic acid so it can be separated from other organics. Apparently it has been
used in some large scale industrial processes.
For obvious reasons you're avoiding aqueous-phase extraction in this case (water-labile solute), but a tert.-amine/HOAc complex might be a starting
idea for some other extraction method.
Just a thought.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
