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Author: Subject: Acetic anhydride, the 2nd.
Esplosivo
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[*] posted on 22-4-2005 at 05:35


Interesting, care to elaborate how this works out. I gather that acetone is passed through the hot copper tube for pyrolysis, but what are the rest of the connections, and how is the ketene vented to acetic acid? Thanks.

I am myself preparing a ketene generator on a larger scale so to produce at least 1Lt of acetic anhydride per run (relatively short time of say 5 hours). I intend to use a set-up as shown on patents mentioned by Organikum, using gas heating (since electricity where I live is expensive and totally unreliable, and gas is cheap). I will post about this project at around mid-summer, when I hope I will have completed the whole thing.




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vulture
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[*] posted on 15-6-2005 at 12:52


This may be slightly off-topic, but I don't think it warrants a new thread.

My Roempp chemical dictionary claims acetylchloride can be made from acetic anhydride and CaCl2, however, no procedure is listed and google doesn't seem to know the answer either.




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S.C. Wack
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[*] posted on 15-6-2005 at 13:24


I came across a reference somewhere else, it may be what they are talking about. The yields in this article are not the greatest.

Attachment: helv_chim_acta_36_2021_1953.pdf (28kB)
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[*] posted on 21-6-2005 at 01:08


P2O5 and GAA dont reakt to the anhydrid or keten!
the BP. of the GAA was than 110°C :o
Quote:

I would then propose distilling off the rests of SO3 at moderate temperature(can be recycled by dissolving in conc. H2SO4), followed by distilling off as much of the lower boiling acetic acid as possible and then the last fraction should yield an azeotropic mix of acetic anhydride and acetic acid, which is far from being pure acetic anhydride i presume, but i´m sure it could be used in most nitrations where acetic acid is added to the anhydride anyway.

u cant destill SO3 out of H2SO4 that easy,
the lower the SO3 conz. is, the higher is the temp. u need to destill it off from H2SO4
means: the last % SO3 destills over near the BP. of H2SO4 :(
u also cant destill the GAA or the anhydrid out that easy...
its the same as when u try to destill HNO3 out of H2SO4, the more H2SO4 u use, the higher is the temp. that is need to destill the HNO3 out, but HNO3 isnt stabel anymore at >150°C so u have much NO2 in it :(
same hapens whit the GAA (and the anhydrid?) the stuff just gets dehydratet to carbon!
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[*] posted on 21-6-2005 at 11:39


I'm intrigued by the idea that, because ketene reacts with water, it can't be a real health hazard.
Phosgene also reacts with water but worked adequately well as a war gas.
Methyl isocyanate reacts violently enough with water to blow up factories like Bhopal. That didn't seem to stop it causing further damage to a lot of people.
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Dave Angel
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[*] posted on 24-7-2005 at 10:42


I've been tinkering around with a ketene lamp set up for a while now but only just made a first run.

I'm using a coil from a heat gun which I've trimmed down to fit through a 34/35 joint into a 3-neck flask. The 19/26 side necks take an addition funnel and condenser. The wires for the coil come out of the side arm of a T-shape adapter, 34/35c-19/26s, having a side arm for push on hoses. I use the 19/26 socket to feed argon in before plugging it and running the set up.

Aside from the coil being in the boiling flask (permitting very little acetone to be in the system at one time) the set up is otherwise much like Vogel's.

Having purged the system with argon and refluxed the acetone a little, I turned the coil on and made the following observations.

The hot melt glue used to seal the gap where the wires come out leaked and melted in spite my efforts to cool it with damp cloth or duct/PIB tape it up. I had expected this to be the weakest point and it was what ultimately made me turn the thing off after about 30 mins.

During use, a light grey 'mist' went up the primary condenser (water-coil) and down the secondary, air condenser. Some liquid (~1 mL) collected in the separating funnel.

The gases were passed through hot, deionized water (500 mL) and then burnt. The end gases were very flammable and the water became quite acidic (indicator solution goes fully red) but with minimal, if any, change in density.

Having turned the thing off, the coil had become coated in some hard soot. Interestingly it was clean close to where the acetone pooled in the bottom of the flask and more carbonised higher up.

I took my mask off for a moment to see how the air was (after opening the apparatus up) and the smell was something like that spray foam string stuff you can get for parties etc. The small volume of liquid that was collected also smelt strongly, perhaps slightly different to the air or perhaps just more concentrated.

So there's some issues to work out in order to make a long run safe and productive:

The wires. I've thought of epoxying them in, but that has a certain finality to it and may still not stand the heat. Any other thoughts?

Carbonisation. A little oxygen creeping in? Over-decomposition? The coil was at a dullish red glow with the variac on 45% so lower/higher is easy to try out.

Liquid collecting: Ketene polymerisation products? If not, acetone may be escaping the condenser, which isn't ideal, but can probably be separated later.

Another concern is that there is nothing forcing/drawing the gases through the system. If they hang about in the boiling flask too long they may be decomposing to far, causing the carbonisation. Maybe some suction at the end?

Any ideas?
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[*] posted on 24-7-2005 at 11:45


If there was any moisture in your apparatus (from the glue, maybe), that liquid would probably be acetic anhydride.
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[*] posted on 24-7-2005 at 18:09


Isn't diketene a liquid also?

sparky (~_~)




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Dave Angel
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[*] posted on 26-7-2005 at 06:29


I doubt it's AA; it smells nothing like it and even if something were masking the smell it would still have a stinging effect on the nose and eyes.

We are thinking the same thoughts sparkgap... diketene is a distinct possibility and it's formation after the condenser would explain how it escaped reflux.

I can't seem to freeze it, even at -20°C, (mp -7°C to -6.5°C), but that may be due to impurities, maybe some escaped acetone. I tried decomposition in water but the smell of the sample is close to that of acetone and so that particular test is difficult to detect. I did think I smelt acetone strongly from it the first time I tested this, but I came back later, tested it again and wasn't so sure. Perhaps it had further polymerised to the point where it did not decompose in water. It also causes a pH drop in water so I may be getting no ketene to interact with the water later on in the apparatus.

I have managed to solve a couple of problems, in my head at least.

I intend to feed the coil wires up through a 34/35 reflux condenser with a plain end. There at the top, the joint will be safe from conducted heat due to distance and, if I run the condenser, hot acetone.

I also intend to apply something of a vacuum to the end of the set up to draw the vapours through. I'm not too sure about using a full vacuum though, as that will make the acetone more difficult to reflux.

So those are the major hurdles, I should be able to make another attempt as soon as I make the new ideas reality and clean this crap off the coil!
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[*] posted on 27-7-2005 at 03:01


I checked the container of diketene in my lab the other day and was able to confirm that it is indeed liquid at ambient conditions.

"...It also causes a pH drop in water..."

IIRC, diketene hydrolyzes to acetoacetic acid in water. That may be it. ;)

sparky (~_~)
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Dave Angel
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[*] posted on 27-7-2005 at 07:06


Thanks for the info. From what I could find, diketene is said to decompose into acetone and CO2 - which, it is now clear, must come from decarboxlyation of initially produced acetoacetic acid! The acetone was what I was trying to detect (to indicate possibility of it being diketene), above, but perhaps it needs to be sealed up with water, heated and allowed to decarboxylate.

I guess the acetoacetic acid and then dissolved CO2 would produce the acidity, certainly acetone only produces a yellow colour with indicator solution. This is the problem you see; I was relying on the pH change to indicate ketene interacting with my flask of deionized water to produce acetic acid. With diketene having the same effect it's going to be tougher to determine if ketene is being produced. Hopefully the measures I've outlined above will minimise the chance for diketene formation.

I'm attaching a view of the set up. I also have closeups of areas that I can post if anyone is interested.

[Edited on 7/27/2005 by Dave Angel]

wholesetup.jpg - 260kB
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[*] posted on 28-7-2005 at 05:55
BA + AA


For those benzal chloride buffs out thar.
Dont know if this is within the scope of this thread,but it seems easier than acetylchloride/ketene methods.
Sorry if this has been posted previously.

161 parts of benzalchloride are heated with 180 parts of thoroughly dried sodium acetate for 14 hours at 160-170 (C'. The product is worked up by distillation and in this manner considerable proportions 50 of acetic anhydride and beuzaldehlyde are isolated.

The patent says that the addition of GAA can improve yield to 90% blah blah blah.


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CD-ROM-LAUFWERK
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[*] posted on 6-8-2005 at 23:56


i found this text in the ullmann 7th edition:
Quote:

Production via Ethylidene Diacetate. Addition of acetic acid to acetylene in the presence of mercury(II) salts yields ethylidene diacetate [542-10-9], CH3CH(OCOCH3)2, which decomposes into acetaldehyde and acetic anhydride at 130 – 145 °C in the presence of acid catalysts (e.g., ZnCl2). This process was developed by the Societe Chimique des Usines du Rhône on an industrial scale in 1914 but is now without importance.

there are no reaktion informations, such as temperatur and pressur, given,
but i hope u guys know them ;)
so, is it possible to buble C2H2 into GAA, in the presence of Hg2+ cat., at temperaturs under the bp. of GAA and normal pessur to get ethylidene diacetate?

edit:
i searched now a while and found some intresting things:
the temperatur is 60-100°C and the salz used was mercurysulfate (suspension in the GAA?)

[Edited on 7-8-2005 by CD-ROM-LAUFWERK]
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