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Author: Subject: Acetic anhydride preparation
chemoleo
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[*] posted on 28-11-2005 at 14:22


BASF, I thought this was very interesting.
Much easier than going via acetylchloride, and Br2 isn't really *that* hard to make or get.

Anyway, I wondered, what was this about with using NaAc, Br2 and *sulphur*?
How is that supposed to work?

Edit: Oh I see, it's a one-pot synth, where S2Br2 is formed which is continuously recycled?
That almost sounds too good to be true!

[Edited on 28-11-2005 by chemoleo]




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[*] posted on 28-11-2005 at 14:26


I suppose it works somewhat like chlorinations using catalytic amounts of S or P (a la chloroacetic acid). Organikum has made posts about that on here.
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[*] posted on 29-11-2005 at 08:12


Ash on my head. I was ignorant and arrogant. Maybe where you live its over the counter and cheap.

For my part, i have not seen yet bromine salts that cheap where i live, but of course, when recycling of Br2 as a one-pot-reaction works, it may be a satisfactory method, though there are many alternatives.
At the moment i´m going for a ketene-lamp-setup based on the info in Vogel. But as always, practice is always a little bit more complicated than theory...

[Edited on 29-11-2005 by BASF]
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[*] posted on 30-11-2005 at 01:18


From Rhodium:
Quote:
Acetic anhydride from sodium acetate, using S2Cl2

Translated from russian by Antoncho

Prepare 100g freshly fused NaOAc and 65g S2Cl2. A small quantity of NaOAc is placed in a thin-walled glass cooled in an ice bath. To this is added some sulfur chloride, the mixtr is vigorously stirred w/a wooden spatula, not allowing the temp to rise. Then some NaOAc is added again, and the process is repeated several times until all is mixed in. The semi-liquid mass is transferred into a 1 liter RBF. The previous operation is repeated 4 times, so that 400g NaOAc and 260 g S2Cl2 total are taken into work. The RBF is then equipped w/a reflux condenser and gently heated on a water bath to ~80-85°C. As soon as the rxn starts, the heating is removed, and in case the rxn gets too vigorous it's cooled w/cold water. After 20-30 min SO2 evolution ceases and the mixture is heated for 10 more min's on a boiling water bath. The rxn product is then distilled off under vacuum, then fractionally re-distilled at ordinary pressure, collecting the fraction boiling between 132-142°C.

For further purification it's distilled with 2-3% KMnO4 or K2Cr2O7 for breakage of sulfurous contaminants (test for their presence: 1 ml of the distillate upon neutralization w/pure NH3 mustn't give a dark precipitate on treatment with Pb(AcO)2) The yield is ~90% based on S2Cl2.

Another similar synthesis, generating sulfur chloride in situ:

Mix quickly and thoroughly 205-215 g of pulverized fine NaOAc and 10g dry sulfur powder, the mixture is quickly transferred to a wide-mouth 1 liter RBF and wetted w/25 ml acetic anhydride. Into the flask through the rubber cork extend 1) a wide tube for chlorine in-flow 2) an overhead stirrer, which is sealed with the aid of a piece of rubber tubing greased with vaseline and 3) an out-leading tube for excess Cl2 release. The flask is immersed in an ice-bath. Chlorine is initially passed in very carefully, with frequent stirring or shaking, over the passage of time the rxn gets hotter and more and more liquid, so the stirrer may bee after some time rotated with a motor. Chlorine stream should bee regulated so that almost all of it is absorbed. When the reaction mixture stops heating and Cl2 is no longer taken up, the rxn contents are distilled in vacuo at oil bath temp ~150-180°C, then redistilled at ordinary pressure, collecting the fraction boiling between 132 and 142°C. Yield ~90%.


The second method looks most promising.

Thought I'd link to this since this method works well for easy Cl2 production, much better than bleach + acid IMO.
sciencemadness.org/talk/viewthread.php?tid=2972

[Edited on 30-11-2005 by Chris The Great]
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[*] posted on 30-11-2005 at 18:57
industrial method


This one works as I used it several times.

THIS METHOD IS INTENDED FOR PROFESSIONAL CHEMISTS ONLY

This reaction is very exothermic so it can be very dangerous if you are not used with this kind of chemistry.

In a 3-neck flask equipped with a mechanical overhead stirrer, a reflux condenser, nitrogen inlet, thermometer. Put 1 equivalent of very dry sodium acetate. Add 0.97 equivalent of acetyl chloride DROPWISE AND VERY SLOWLY while stirring the thick mixture to avoid reagents build-up. For safety issues, you can start with a small amount of sodium acetate and add a deficit of acetyl chloride until you get a mobile mixture, then add more sodium acetate and more acetyl chloride and repeat until you get the desired mass. The only products are acetic anhydride, sodium chloride and sodium acetate (because you use a deficit of acetyl chloride). You distill from the pot. You get very pure stuff (over 99% purity if you got far away from water).

For a first timer, start on a 100 g scale and go on as you feel comfortable. This on is not easy to scale-up because of safety reasons. Good luck.

I made a batch of 1.5 kg (80 % yield) recently and I have been using this reaction for 4 years now.
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[*] posted on 30-11-2005 at 20:30


I may be wrong, but wasn't this whole thread about an easy way to/around acetyl chloride?
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[*] posted on 1-12-2005 at 03:21


As chemoleo just said, around.

We have all heard of the acetyl chloride method and want something original done with chemicals we can actually obtain.
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[*] posted on 1-12-2005 at 09:02


Acetyl chloride can be obtained by reacting benzotrichloride (from toluene + chlorine) with glacial acetic acid in the presence of ZnCl2, but production of benzotrichloride is very lengthy (production of benzyl chloride already is!), unpleasant (lachrymator!) and uses insane amounts of chlorine.
Could be worth a try if you have a fume hood, suitable apparatus and a lot of free time.

Maybe I'll eventually try one of the sodium acetate + chlorine (bromine) + sulfur source (like elemental S or thiosulphate or S2Cl2) recipes if I feel like it.
But I could just try to order the anhydride, it's watched but not illegal to possess (in contrast to things like piperonal, ephedrine or phenylacetone, of which the sole possession is illegal).

That's my planned procedure (I'll work with a tenth of the amounts stated, and of course without Ac2O added at the beginning):

Mix quickly and thoroughly 205-215 g of pulverized fine NaOAc and 10g dry sulfur powder, the mixture is quickly transferred to a wide-mouth 1 liter RBF and wetted w/25 ml acetic anhydride. Into the flask through the rubber cork extend 1) a wide tube for chlorine in-flow 2) an overhead stirrer, which is sealed with the aid of a piece of rubber tubing greased with vaseline and 3) an out-leading tube for excess Cl2 release. The flask is immersed in an ice-bath. Chlorine is initially passed in very carefully, with frequent stirring or shaking, over the passage of time the rxn gets hotter and more and more liquid, so the stirrer may bee after some time rotated with a motor. Chlorine stream should bee regulated so that almost all of it is absorbed. When the reaction mixture stops heating and Cl2 is no longer taken up, the rxn contents are distilled in vacuo at oil bath temp ~150-180°C, then redistilled at ordinary pressure, collecting the fraction boiling between 132 and 142°C. Yield ~90%.


[Edited on 1-12-2005 by garage chemist]

[Edited on 1-12-2005 by garage chemist]
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[*] posted on 1-12-2005 at 10:52


This sounds very interesting and challenging. Have you worked with gaseous chlorine before? (I have not - yet.) Do you have a small variable speed overhung mixer that you could use? Of course a hood (or the great outdoors) would be mandatory as you will have the release of chlorine not only out the exit port but at the imperfect shaft seal. Good control of the chlorine generator would also be important I would think.

How old is this procedure and where did you get it?




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[*] posted on 1-12-2005 at 11:16


Yes I have worked with chlorine before, it's no big deal with hood and proper apparatus.
Remember to properly dry the chlorine, as dry reagents are imperative here.

I don't have an overhead stirrer, the mixture will be stirred manually at the beginning with a glass rod from time to time, the chlorine inlet tube will be removed during stirring (I'll work in a one-neck NS14/23 100ml rbf).

I'll recrystallize my sulfur from hot toluene, because flowers of sulfur contain traces of H2SO4 due to autoxidation that coat the particles and make reaction with gases difficult.
The crystalline sulfur will be ground immediately before use, exposing fresh surfaces. Only one gram is needed (I need to check the stochiometry of the reaction- I assume that the sulfur gets oxidised all the way to sulfate, that's the only way such a small amount can suffice) in my batch with 20,5g NaOAc.
Hmm, I should make more anhydrous sodium acetate to be able to make bigger batches...

The necessary vacuum distillation with an oil bath will be a hassle, since vacuum is really required here (the Ac2O forms during the distillation, not before, the same thing as with S2Cl2 + acetate). I'm not a friend of vacuum distillations, as I have experienced numerous problems with them due to the claisen stillhead flooding. NS14/23 is really small for vacuum work.

The procedure is from rhodium's archive, the entry on carboxylic acid anhydrides. I have no idea to the origin of it.
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[*] posted on 1-12-2005 at 18:54


What are the chemical reactions for this synthesis?

I have done 2 vacuum distillations during organic class. The only problems I had were stopping leaks and a poor vacuum source. I have found that having a Hg manometer or a vacuum guage is very useful. The only thing that would stop me from using one is an incompatibility of materials.




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[*] posted on 1-12-2005 at 20:50


These are the reactions:

Cl2 + 2S -> S2Cl2

4NaOAc + 2S2Cl2 -> 4NaCl + 3S + SO2 + AcOAC


The second step is actually a two step reaction:

4NaOAc + 2S2Cl2 -> 4NaCl + 2AcO-S-S-OAc

2AcO-S-S-OAc -(heat)-> 3S + SO2 + AcOAc

This was also from the rhodium page. It was very useful so if you have a rhodium archive check it out. It's in the organic precursors section and is titled "Acetic anhydride, Propionic anhydride and Acetyl chloride'

It includes several other procedures as well but they are not OTC.
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[*] posted on 2-12-2005 at 03:20


The Rhodium archive can be found here, just scroll to the bottom of the main page:
www.designer-drugs.com

[Edited on 2-12-2005 by garage chemist]
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[*] posted on 2-12-2005 at 14:45


I just tried out the mentioned procedure.

I recrystallized a small amount of sulfur from toluene and thoroughly dried the crystals with a heat gun until the toluene smell had completely disappeared.

1g of this was ground together with 20,5g anhydrous NaOAc with mortar and pestle and transferred into a 100ml rbf.
A chlorine generator was charged with 20g of TCCA and 35ml 25% HCl (nearly two times the theoretically needed amount, since I knew that a lot of chlorine would escape without reacting).
The chlorine was dried in a wash bottle with concentrated H2SO4.

The chlorine was led through a flexible silicone tube into a bent glass tube that served both as chlorine inlet and also as a manual stirring rod.

On slowly adding the chlorine to the powder, nothing happened. I stirred well, but the powder did not change appearance at all.
Knowing that the solvent acetic anhydride was missing, I added a single drop of disulfur dichloride (selfmade, really old) instead and stirred it well. Still no visible signs of reaction.
The space above the powder was green from the chlorine, the powder was as powdery and cold as before.

I eventually heated the flask from the outside using a bunsen burner, and this finally started the reaction. No more chlorine was escaping, it was completely absorbed from the powder. The powder started sticking to the sides of the flask and heated up from the reaction. I had to hit the flask with a wooden stick in order to break loose the sticky mass.
When the chlorine generator had finished reacting, the powder had become a single wet mass (not liquid! It was crumbly and sticky almost until the end of reaction!), and the space above it was green again, indicating a complete reaction.

I distilled it in vacuum, which was easier than I thought. A clear slightly yellowish liquid came over at about 45°C (didn't watch the thermometer).
I redistilled it at atmospheric pressure over a bit of sodium acetate because I assumed that the yellowish color was from disulfur dichloride, which cannot be removed by distillation alone.
At 130-140°C, 6ml of colorless liquid distilled. Nice! I thought.

I added a drop of the liquid to water, and it sunk to the bottom as an oily layer which very slowly dissolved on swirling. There was no noticeable evolution of heat.
This raised the first doubts about the identity of the product.
I the smelled the liquid, and the smell was bad and clearly different from acetic acid.
It smelled "chlorinated". It reminded me of the stuff I got from incomplete chlorination of ethanol.
I added some of the liquid to ethanol and some sodium bisulfate as catalyst and boiled the mix for a few seconds, then I added a lot of water. No ester layer separated, and there was no smell of ethyl acetate. It still smelled like the product.

The synthesis was a disappointing failure.
The product has the same boiling point as Ac2O, but smells very different and shows none of the characteristic reactions of Ac2O.

I hope that this report of my unsuccessful synthesis helps to keep other members from repeating my experience.


My next attempt at Acetic anhydride will either be the thiosulphate/chlorine process that I translated earlier in this thread (I need to buy sodium thiosulphate first as I don't have any) or the bromine/sulfur process that was mentioned above as being successful once.
Either way, I first need to make more anhydrous sodium acetate before I can continue research.

[Edited on 2-12-2005 by garage chemist]
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[*] posted on 2-12-2005 at 15:12


Does chlorine react with sodium acetate? If so, maybe you got too much of that reaction in comparison to the S + Cl2 and ended of with some strange sulfur compounds.

Or what you said. that sounds good too.
[Edited on 2-12-2005 by stygian]

[Edited on 2-12-2005 by stygian]
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[*] posted on 2-12-2005 at 15:19


No, otherwise the powder would have reacted from the beginning. The sulfur is supposed to react here.

As to the presumable reason for the failure: It is known that Ac2O acts as a catalyst for the chlorination of acetic acid to chloroacetic acid.
If now a trace of acetic acid was present, this could have reacted with the chlorine, forming HCl in the process which instantly liberates acetic acid from the acetate, this gets chlorinated again and so on, producing chloroacetic acids as the main product.
That's my theory.

I think I'll try the bromine/sulfur process next, it sounds the most promising and the bromine can be completely recycled afterwards.

[Edited on 2-12-2005 by garage chemist]
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[*] posted on 2-12-2005 at 15:29


Was sulfur dioxide generated during the reaction? That would be a good indication if the reaction was actually proceeding as it should.
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[*] posted on 2-12-2005 at 17:15


Except for adding the initial Ac2O you followed procedure. So either that was a vital step or the procedure is no good. I have no experience with the Hive's procedures. Are they usually good? Or, what is the Hive's general reputation?



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[*] posted on 2-12-2005 at 17:17


From reading hive posts, rhodium seemed to know his stuff, i dont think he posted stuff that didn't work. Though I could be wrong.
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[*] posted on 3-12-2005 at 03:02


Quote:

As to the presumable reason for the failure: It is known that Ac2O acts as a catalyst for the chlorination of acetic acid to chloroacetic acid.


I thoat that initially added acetic anhydride acted as a solvent that helped to adsorb chlorine and transfer it faster to the partially dissolved acetate which supposed to evolve heat and initiate the reation..

Btw, GC, you sure that the ethyl acetate test you've did gives accurate results on such small scale?

Found some interesting reaction involving another chloride than phosphorous chloride..

US pat. 944372 where SiCl4 is added to sodium acetate. Depending on proportions you either get chloro anhydride or acetic anhydride:

SiCl4 + 2CH3COONa --> 2NaCl + SiO2 + 2CH3COCl

SiCl4 + 4CH3COONa --> 4NaCl + SiO2 + 2(CH3CO)2O

Now the interesting part is that SiCl4 is much easier to prepare than phosphorous chlorides.. In my nonorg book, they either let chlorine through 300-400C silicone powder or 600C silicone-iron alloy prills.

The silicone obtained from reduction of SiO2 by Al/S is in form of small crystalls.. maby it will suit this purpose..

[Edited on 3-12-2005 by frogfot]

[Edited on 3-12-2005 by frogfot]
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[*] posted on 3-12-2005 at 09:31


Quote:
Originally posted by frogfot
Now the interesting part is that SiCl4 is much easier to prepare than phosphorous chlorides.. In my nonorg book, they either let chlorine through 300-400C silicone powder or 600C silicone-iron alloy prills.

The silicone obtained from reduction of SiO2 by Al/S is in form of small crystalls.. maby it will suit this purpose..


*Cough* Silicon, NOT siliconE.

You can also get powdered silicon from magnesium, magnalium or aluminum and powdered silica, which is horrendously cheap as powdered flint at the ceramic supply. Reactivity seems to suck though, the ground product doesn't want to dissolve in molten aluminum. It might need a wash in HF acid... :o

Al/S reduction is hotter and leaves fused globules, that should work fine.

If you need ferrosilicon 75%, I have some on hand. Fleaker has some too, as I recall.

SiCl4, like TiCl4, can be prepared by passing chlorine through a heated mixture of SiO2 and C, I think.

Tim

[Edited on 12-3-2005 by 12AX7]




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[*] posted on 3-12-2005 at 13:25


Quote:

*Cough* Silicon, NOT siliconE.


Lol, thanks :)

I'd go with reduction of homemade silica, most of it is usually in very fine powder.
Just thoat that Al/S reduction may be a pain due to sulfides.. Reaction may go with Al alone if mix is priorly heated alot with a gas burner and then lighted (heard this somewhere).

The chlorination of silicon could be done in usual dest equipement, heating the reaction flask with gas burner (I'd guess temp control is not that critical). Books advise to use oxygen free chlorine, otherwise SiO2 will form on surface and reaction will slow down..
So, I'd guess using chlorine prepared by KMnO4/HCl, MnO2/HCl or electrolysis would not be recommended..

One drawback of the SiCl4 preparation would be the incompleate consumption of chlorine. I find this a pain since all practical methods of chlorine preparation are quite expensive in this country.. Heh, don't tell me about ass cheap TCCA, since here they take about 40UD$/2kg for it. :o :(

Any info on required temperature in SiO2/C/Cl2 reaction?

[Edited on 3-12-2005 by frogfot]

[Edited on 3-12-2005 by frogfot]
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[*] posted on 4-12-2005 at 04:21


Yesterday evening I made a rather large batch of bromine, 50g theoretical yield. I used CaBr2 + NaClO3 + HCl.
I distilled it from the reaction mix, separated the bromine from the water layer, added some conc. H2SO4 to dry it (very important for Ac2O production!) and let it stand overnight. I'm going to distill the dry bromine today.
It's the first time that I have enough bromine to feel its density.

If I have time, I'l also do the subsequent Ac2O production from Br2, S and NaOAc today.
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[*] posted on 6-12-2005 at 14:29


Today I tried out the bromine method.

16,1g dried distilled bromine were measured, and 1,1g sulfur powder added to it and swirled. The sulfur rapidly dissolved and there was a noticeable rise in temperature, but it quickly returned to ambient temp after the sulfur had dissolved.
22,2g anhydrous sodium acetate were ground in a mortar and quickly put into a 100ml rbf.

The sulfur-bromine mix was poured into the rbf with the NaOAc, and a strongly exothermic reaction immediately set in. Big nasty surprise! The bromine boiled violently and dense brown clouds billowed out of the flask. I immediately grabbed a bucket of cold water and immersed the flask in it, this stopped the bromine from further escaping.
I stirred the reaction mix and removed the flask from the water bath. It was brown in some places and white in others. On further stirring the entire mix quickly became white and very hot, almost too hot to touch, but all of the bromine had already reacted and nothing escaped.
On further stirring the crumbly mass slowly turned into a thick slurry and cooled down.

I set the flask up for vacuum distillation and distilled under aspirator vacuum. About 7-8ml of liquid distilled at about 40°C.
I had to use a heating mantle since heating with a burner caused severe bumping.
The distillation went slow, since the mass turned powdery where it touched the hot glass and insulated the slurry on the inside. But I distilled until everything was dry.

The liquid was redistilled under standard pressure, it distilled between 120 and 140°C, so it was likely a mix of products.

The resulting clear liquid did not smell very pungent, and distinctly different than acetic acid. It strangely reminded me of propane from refillable bottles.

On adding a few drops of the liquid to 2ml water, it sunk to the bottom and on swirling slowly dissolved. There was no noticeable temperature change.
Some of the liquid was boiled with two times its volume of ethanol, on dilution with water nothing separated. There was a nasty smell that irritated the nose and eyes, this might have been small amounts of ethyl bromoacetate, a powerful lachrymator.


The synthesis yields something which looks like Ac2O and distills at the same teperature as Ac2O but is not Ac2O.

My father has worked with Ac2O a long time ago and told me that it smells extremely pungent, much worse than glacial acetic acid.
The stuff from my experiments can directly be smelled without too much irritation.
Also there is no exothermic reaction with water.


These syntheses fail.
I have no idea why they have been published. The inventors either didn't check the identity of the product carefully enough (unlikely) or there is a special trick to them.
It could be the addition of Ac2O at the beginning that "tells" the reaction how it should proceed. Maybe it serves the purpose of removing every trace of water from the reactants before reaction. That's the only really logical explanation.

Either way, it doesn't make any difference if we can't get them to work or if they can't be gotten to work at all.

We need to focus on different procedures. Back to the drawing board.

Left are:
  1. the ketene process
  2. the N2O4 + acetate process
  3. the S2Cl2 process.
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[*] posted on 6-12-2005 at 15:45


"The sulfur-bromine mix was poured into the rbf"

Perhaps you might want to try this again with a different technique.
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