Sciencemadness Discussion Board

Acetic anhydride preparation

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chemoleo - 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]

stygian - 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.

BASF - 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]

Chris The Great - 30-11-2005 at 01:18

From Rhodium:
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.

[Edited on 30-11-2005 by Chris The Great]

industrial method

jack-sparrow - 30-11-2005 at 18:57

This one works as I used it several times.


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.

stygian - 30-11-2005 at 20:30

I may be wrong, but wasn't this whole thread about an easy way to/around acetyl chloride?

neutrino - 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.

garage chemist - 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]

Magpie - 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?

garage chemist - 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.

Magpie - 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.

Chris The Great - 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.

garage chemist - 2-12-2005 at 03:20

The Rhodium archive can be found here, just scroll to the bottom of the main page:

[Edited on 2-12-2005 by garage chemist]

garage chemist - 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]

stygian - 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]

garage chemist - 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]

Chris The Great - 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.

Magpie - 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?

stygian - 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.

frogfot - 3-12-2005 at 03:02


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]

12AX7 - 3-12-2005 at 09:31

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.


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

frogfot - 3-12-2005 at 13:25


*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]

garage chemist - 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.

garage chemist - 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.

S.C. Wack - 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.

stygian - 6-12-2005 at 17:41

Yes, as the propionic procedure (only substituting acetate for propionate) does say to 'add, with stirring, keeping the temp under 50C'

Magpie - 6-12-2005 at 20:16

Garage chemist wrote:


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"

Did you purposely leave out the "acetyl chloride + acetate" process? Is acetyl chloride disallowed?

sparkgap - 6-12-2005 at 20:52

Maybe not disallowed, Magpie, but for me, I don't see the point of making acetic anhydride if you have acetyl chloride, and vice-versa. They are for the most part interchangeable in syntheses...

sparky (~_~)

stygian - 6-12-2005 at 21:19

Ok, so, because gc decided to totally ignore the procedure partway through, we should focus on different methods? o-kay.

Magpie - 6-12-2005 at 22:54

OK sparkgap. I thought it was something like that but I just wanted to make sure. Are we then just trying to make a powerful reagent without using the holy grail of organic chemistry? ;)

garage chemist - 7-12-2005 at 03:33

Sorry, it seems like I haven't expressed myself correctly.
Of course everyone can try the bromine/sulfur process if he wants, maybe someone has more luck. I just stopped further research on this because I don't like the method and the product is apparently impure with bromine compounds.
The procedure for acetic anhydride didn't specify cooling, nor did the report of the successful preparation. It also didn't say to add the bromine-sulfur miy gradually. Maybe that's important.
Also there's the problem of the Ac2O addition on the beginning, which we aren't able to do.

I left out the acetyl chloride process because acetyl chloride is just as hard to prepare as acetic anhydride and, like sparkgap said, it is interchangeable with the anhydride in syntheses.

frogfot - 10-12-2005 at 01:22

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

Boiling point is quite heavy evidence of right product.. I still think that you've got Ac2O.
Will Ac2O really evolve heat when mixed with water, specially in less than 5g quantity? It suppose to hydrolise quite slowly.

Easier would be to take a known quantity, reflux for some time with water and titrate the formed acetic acid.

IPN - 10-12-2005 at 02:18

This is what Practical Methods of Organic Chemistry (Gattermann) says about detecting acetic anhydride:


5 c.c. of water are treated with 0,5 c.c. of acetic anhydride. The latter sinks to the bottom and does not dissolve even on long shaking. If the mixture be warmed, solution takes place.


2 c.c. of alcohol are added to 1 c.c. of acetic anhydride in a test-tube, and heated gently for several minutes. It is then treated with water and carefully made slightly alkaline. The acetic ester can be recognised by its characteristic pleasant odour.


Add 1 c.c. of aniline to 1 c.c. of acetic anhydride, heat to incipient ebullition, and then, after cooling, add twice the volume of water. The crystals of acetanilide separate out easily if the walls of the vessel be rubbed with a glass rod.

garage chemist - 10-12-2005 at 05:02

Ah, thanks a lot!

Good that I saved the product from the last try.
I honestly did hear the exact opposite of the first test, namely that acetic anhydride reacts violently with water.
Seems like there's still a chance that I have gotten Ac2O.
I'll boil some of this longer with ethanol and look if I get some ethyl acetate.
I also have aniline, which I'm going to use for the acetanilide test.

Madandcrazy - 17-1-2006 at 07:48

I told madscientists opinion, the method oxidizing acetic acid beside other methods shoult walk, but in oxygen free atmosphere i think it`s not necessary.
A metal or metal oxide catalyst should walk, copper, chromium ... and the the acetic acid/acetic acid anhydride should passed often thrue the catalyst.

A suggestion is:

Place the acetic acid in a beaker, the beaker is connected with a claisen to a long glas-tube with the catalyst inside (glas wool, metal oxide) and a another beker is connected with a claisen to the end of the glas-tube. The acetic acid is destilled over the bp. and the tube with the catalyt is heated > 140 gedree celcius until the liquid is passed over. The procedure is repeated often until the acic acid is oxidized. (purifying the anhydride by destilation over the bp. when the rest of the aa content is removed by destillation < 138 gegree celsius.)

I think the method should walk.

[Edited on 19-1-2006 by Madandcrazy]

garage chemist - 17-1-2006 at 09:42

Madandcrazy, that would just give Ketene and not Ac2O.
Also 140°C are not enough, by far.

As to my product: I repeated the ester formation with an excess of Ethanol, and the smell of ethyl acetate is only faint, even after 10 minutes of boiling.
Pouring into water gives no ester at all.

Also, someone who uses to work with Ac2O smelled my product, and said that it was highly impure since the Ac2O he handles smells much different.

For Ac2O I am now going the same route as with carbon disulfide: I am trying to order it (250 ml).
It is a "watched" chemical where I live, but its possession is not forbidden.
I will have to fill out a lot of paperwork and send a copy of my personal identity card, give information about my type of education and so on.
This is more of an "experiment" to find out if you will actually get Ac2O as a private person if you fill out all of the papers or if this is just "bluff" to deter most people from ordering and you actually will never get it.

jimmyboy - 17-1-2006 at 20:57

Has anyone actually performed the bromine path to anhydride or is that just theory? it seemed kind of vague - it mentioned keeping the flask in cold water so im guessing you need to keep the reaction slow and cooled - the rest seems pretty easy - make some bromine - dry sodium acetate in an oven - melt some sulfur and crumble into the mix - fraction distill - is the anhydride absolutely needed to start with?

Madandcrazy - 19-1-2006 at 07:22

garage chemist, i meant the oxidation of acetic acid is surely possible with this method between the boiling point, the decompositions point of the acetic acid and the acetic acid anhydride. The temperature is not precise know by me.

12AX7 - 19-1-2006 at 15:14

Why would you want to oxidize acetic acid? The goal is acetic anhydride, meaning you've removed a water molecule, not like, acetic...oxide...or something. Besides, oxidizing the most active(?) part would just give CH4 or CH3OH, and CO2.


Madandcrazy - 22-1-2006 at 07:55

Read in the forums for removing water of delute acetic acid to obtain glacial acetic acid. Oxidizing of acetic acid is only a easy way ;) when no chemicals available, i think rather than
a industrial method.

[Edited on 22-1-2006 by Madandcrazy]

garage chemist - 10-2-2006 at 04:31

I finally received my order with acetic anhydride from a chemical supplier today (250ml).

And bad news: it smells very different than my product from Br2+S+NaOAc. The AA from the supplier smells very pungent and strongly stings in the nose.

I'm going to make some nice syntheses with it, the first one being cinnamic acid (with benzaldehyde, which I also got in the order today).
The next thing could be acetylcellulose.
And when I am successful with my synthesis of salicylaldehyde, I'm going to make cumarin (is said to smell very nice).

learner - 12-3-2006 at 19:17

Anyone have any experience with this method of Acetic anhydride synthesis from Dick's encyclopedia.
Mix in a glass retort, well fused acetate of potassa with half its weight of chloride of Benzoyle, apply gentle heat, collect the liquid that distills over.
Interested in opinions.

garage chemist - 13-3-2006 at 07:56

Originally posted by learner
Anyone have any experience with this method of Acetic anhydride synthesis from Dick's encyclopedia.
Mix in a glass retort, well fused acetate of potassa with half its weight of chloride of Benzoyle, apply gentle heat, collect the liquid that distills over.
Interested in opinions.

This will produce acetyl chloride, since there is an equilibrium between sodium acetate + benzoyl chloride and acetyl chloride + sodium benzoate.
Because the acetyl chloride has a low boiling point it can be constantly distilled off, shifting the reaction to the right.

Reacting this acetyl chloride with anhydrous sodium acetate will make the desired acetic anhydride.

However, maybe the proportions in the above preparation are adjusted to 2 mol NaOAc and 1 mol C6H5-COCl, this should directly give acetic anhydride since the acetyl chloride would react further with the excess of sodium acetate.
Though the so- produced acetic anhydride would contain acetyl chloride. It should be fractionated in order to get rid of this.

S.C. Wack - 19-3-2006 at 22:12

In JCS 18, 21 (1865), the author puts 20 grams of dried Pb(II) acetate in each of several glass tubes and adds enough CS2 to produce "on agitation with the acetate, a mixture of a creamy consistency. The tubes being then rather more than one-third full, were sealed and heated in the oil bath, to a temperature of 165C. The mixture quickly assumed a black colour, and after some hours heating, one of the tubes, by exploding with great violence, gave warning that a large amount of gas had been liberated. After this it was found advisable to open the tubes once a day, in order to let the carbonic acid escape; and with this precaution the digestion was continued, till it was found that that on opening the tubes, only a slight rush of gas took place."

The liquid was decanted, and the wet PbS was distilled to dryness, the distillate combined with the mother liquor, and the whole distilled. CS2 comes over, then "some acetic acid, with a trace of acetone", and the remainder distilled at 137C.

The author, in his only article published by the RSC, does not give an exact figure nor the most vague hint of yield. This cannot be due to a spareness with words. He also says "Experiments with acetate of silver gave a similar result, with even greater readiness."

kclo4 - 15-4-2006 at 13:26

"I'm not sure, but I think that it's possible that I prepared acetic anhydride by accident today. I mixed 164g CH3COONa (contaminated with a small amount of NaHCO3, around 1-2g) with 75g 94% H2SO4. I then poured that into a flask; began heating it, and condensing the vapors (typical distillation). I noticed a very strange, sickly-sweet odor; very difficult to describe. I got a whiff of a very small amount of it, causing me to choke for a few moments. The condensed liquid (which I got 22mL of, if I remember correctly) was still liquid, showing no signs of imminent freezing, at -10C. Now, if that had been acetic acid, it would have frozen at a far higher temperature than that... acetic anhydride, on the other hand, would not freeze until the temperature was FAR lower. I'm postulating that the following reactions were occuring, forming at least a fair-sized quantity of acetic anhydride (there is probably a significant amount of acetic acid remaining). Keep in mind that there was a slight stoichemical excess of sulfuric acid."

I just got done distilling from a mixture of nearly anhydrous sodium acetate 47 grams worth, and about 50 ml's conc. sulfuric acid (30mls added at first then 20mls more to help dissolve the rest of the sodium acetate), I collected about 45mls of distillate, and then I added about 35mls of conc sulfuric acid to that and distilled it again. I got about 25-30mls of distillate that time, the distillate I was thinking was GAA, but I put it in the freezer and it got down to 0 Celsius and it is still very runny and looks like water at room temp, it has a horrible pungent smell at that temp, also from the last distillations I had about 50mls left of the sulfuric acid mix, this was an even darker color then when I started out with, and my H2SO4 is pretty pure, its a brownish tan color, now it is a black color.

To get a better understanding of what this strange compound may be, I took a small pipette and dripped a small amount into a test tube full of water, thinking if it was acetic anhydride it would form a little bit and sink to the bottom, but when the drop went into the water, it formed a solution after a while. as it was dissolving it looked really strange, it was mixing with the water but you could see where it was and see the current in the test tube.
I also added a drop to a tiny bit of sodium bicarbonate and of course, it bubbled

I don't think it is acetic anhydride, but I know it is not acetic acid and if it is it has something else mixed with it, my question is what on earth could this other compound possibly be?

Also when I was doing the distillation I did not use a thermometer and I don't know what temp it got to, but i was carefully and made sure I didn't distill over to much, meaning it couldn't have gotten to hot for the H2SO4 to let off its water.

From both are observations, the acetic acid is definitely turned into some other compound, isn't it?

[edit] It is now -5*C and some crystals are forming so this may be a mixture of GAA and acetic anhydride or another compound

[Edited on 15-4-2006 by kclo4]

12AX7 - 15-4-2006 at 14:43

Keep it cold, let the crystals grow, then pour off the liquid and do some more tests on both. Can you fractionally distill it maybe?


garage chemist - 15-4-2006 at 15:36

This is interesting, I have to try this out too and distill the resulting strange liquid over a column.
Or better redistill over some more anhydrous sodium acetate. This is listed as a method to remove acetic acid impurities from acetic anhydride. Of course it won't work when there is a large amount of GAA in there.

Note that AA smells very different than acetic acid! It has an own, peculiar smell, it also stings in the nose and upper throat about three seconds after smelling it.
GAA just horribly reeks of vinegar, and irritates the hell out of the nose instantly.

Does AA form an azeotrope with GAA?

EDIT: To separate GAA and AA, one could add it to some anhydrous sodium carbonate. No protons here, only in the GAA, which will react with the Na2CO3, but the AA will not react.
Keep adding Na2CO3 until the fizzing ceases, then redistill.

[Edited on 15-4-2006 by garage chemist]

kclo4 - 15-4-2006 at 17:14

Na2CO3 + 2CH3COOH =CH3COONa + H2O + CO2
The reaction makes water, and then that would react with acetic anhydride, to form more acetic acid, correct?

would chloroform extract only the acetic anhydride and leave the acetic acid

Perhaps H2SO4 and acetic acid could be added, and then add chloroform, the chloroform would take the acetic anhydride out of the reaction so then no equilibriums can form with acetic acid, water, sulfuric acid, and acetic anhydride present

now my liquid has been in the freezer for half the day and is -13 C and has the constancy of about pudding, there are crystals and liquid
I opened the reagent bottle and smelled the it for a little while, after around 3seconds of not smelling hardly anything other then a little sting here and there but nothing really, it seemed to all of a sudden have a burning smell, like sniffing in something like maybe say hydrogen chloride gas, it just add a very sharp sting to it. I am pretty sure that my distillate has a low conc of acetic anhydride in it, for most of it is frozen, how ever like I had said earlier I stopped distillation so the hydrated sulfuric acid didn't decompose and let off water. The boiling point of acetic anhydride is much higher then that off acetic acid only a little bit anhydride should have came over, and so it did!

Now I do not know at what temp H2SO4 lets off water, but the boiling point of acetic anhydride is something like 285deg F, and i think sulfuric acid should have let off quite a bit of water by then, so the reason that H2SO4 "doesn't" work to make acetic anhydride from acetic acid is that the reaction: 2CH3COOH = (C2H3O)2O + H2O is shifted to the left when it is heated, and only a little bit of acetic anhydride can make it over. so possibly as vulture was saying maybe add anhydrous MgSO4 to it, to join dehydrating powers to distill more acetic anhydride

Is this hard to understand? I hope I am explaining it good enough!

so the way I am seeing it is that you need to take the acetic anhydride out of the H2SO4 solution, with out using heat.
How might this be done? Chloroform, this should be a good way to extract the anhydride, for it could be done at low temperatures, possible lower then the freezing point of sulfuric acid, the acetic anhydride would change the melting point i would think. maybe a possible way to tell if anhydride is present is to take GAA and it to H2SO4 and see if it will freeze, in the freezer, if it does not, then there would be acetic anhydride in it

tomorrow I am planning on taking the ~30mls of distillate and add it to about 40mls of conc H2SO4 and distill it again, and also add a small amount to chloroform and then take the chloroform out, and let it evaporate off and see what is left!

But what I am saying may just be baloney, for that if acetic anhydride is present in a mixture of sulfuric acid and acetic acid, why would they just make acetate plastic this way, instead of using acetic anhydride? But then again it doesn't mean it will not work this way, now does it?

I also have a question, would ethyl acetate work to extract acetic anhydride in the situation that H2SO4 and GAA are mixed, saying that acetic anhydride is present, or would it disolve?

[Edited on 16-4-2006 by kclo4]

garage chemist - 16-4-2006 at 02:00

You are right, reaction with Na2CO3 produces water. Sorry about that, it was too late yesterday evening, and I couldn't think clearly.

Hmm, I doubt that adding it to H2SO4 and redistilling will do any good. Pure acetic anhydride reacts with H2SO4 in a nasty way, forming some crazy useless compound of H2SO4 with AA. Someone here tried it out in hope to make Oleum, and it didn't work, it just got hot and red and it was a waste of AA.

Your best bet would be a simple redistillation, without anything added. The boiling points of GAA and AA are far enough apart to allow efficient separation with a column or even without a column if you distill slowly enough and constantly watch the thermometer.

Alternatively, try adding a few ml of the mix to an excess of icecold water, stirring gently, and allow to settle. AA, if present, will sink to the bottom as an oil and can be extracted with chloroform. Drying the chloroform with CaCl2 and redistillation should afford some purer AA.
Don't use too little water, or the acetic acid will act as a cosolvent and make the AA dissolve.

Don't use H2SO4 here, it will react with your AA!

kclo4 - 16-4-2006 at 02:08

ok, why not just add chloroform to the GAA/acetic anhydride mix?
it should leave the acetic acid on top and take out the anhydride

What do you think about adding chloroform, GAA and H2SO4 to each other, shaking them and what not, and then taking out the chloroform and distilling it off to leave behind the anhydride?

LOL i waiting till 4 in the moring for a reply tonight haha so if i sound like a moron thats why!

garage chemist - 16-4-2006 at 02:36

I don't know if GAA is miscible with chloroform- I suspect that it is.
Try it out with a small amount.

Your second idea most likely won't work, since you can't apply enough heat to the system. And there's again the question if GAA is miscible with chloroform.

Of what kind is your distilling equipment? Do you have a ground- glass still, or an improvised one with cork/rubber stoppers?
Do you have a thermometer for the stillhead?
Distillation is the best method to separate such a mixture.

[Edited on 16-4-2006 by garage chemist]

kclo4 - 16-4-2006 at 02:44

"Your second idea most likely won't work, since you can't apply enough heat to the system. And there's again the question if GAA is miscible with AA."

Apply heat?

why? that would shift the reaction to the left, and make it stay as GAA with conc H2SO4

I am saying keep the mix cold so the GAA can be dehydrated to acetic anhydride, that will be sucked out the reaction by the chloroform

I have an improvised still, it has 5mm glass rod to condense and connects to a rubber stopper with clear rubber tubing

GAA and AA are soluble in each other, but GAA isn't in chloroform, but I guess once AA was in chloroform it might be, but then again maybe not.

garage chemist - 16-4-2006 at 07:25

You can't expect the H2SO4 to dehydrate GAA to AA in the cold, just like you can't expect H2SO4 to dehydrate Ethanol to ethylene or diethyl ether in the cold.
The reaction needs heat!

And I have to say that your equipment is insufficient to perform such a synthesis successfully. A distillation without measurement of the steam temperature is no real distillation, as you have no indication when which substance is coming over.

A good still can be had for less than 50 bucks from Ebay. Don't buy a large one, instead, get a small one with, like, a 160mm liebig condenser and 14/23 joints (that was my first still, and my only one for years), and a thermometer for it (can be improvised, with a selfmade adapter for an inexpesive electronic thermometer). This is the best investment you can make for chemistry.

kclo4 - 16-4-2006 at 11:54

"You can't expect the H2SO4 to dehydrate GAA to AA in the cold, just like you can't expect H2SO4 to dehydrate Ethanol to ethylene or diethyl ether in the cold.
The reaction needs heat!"

I don't understand why dehydrating acetic acid needs heat. Now I can understand why ether needs heat from this quote off of the Rhodium archive for making diethyl ether

"The temperature of the reaction should be controlled carefully. At temperatures below 130°c, the reaction is too slow and mostly ethanol will distill. Over 150°c, the ethyl sulfuric acid decomposes, forming ethylene instead of combining with ethanol to form ether."

However they are making it sound like it does happen at a lower temperature by saying "At temperatures below 130°c, the reaction is too slow and mostly ethanol will distill"

But I must be over looking something or not?
Acetic acid and sulfuric acid don't form any compounds when mixed like ethanol and sulfuric acid do, correct?

Well if it cant be done, then it might be possible to make it like one would make diethyl ether? The reason I think this is because when GAA is distilled at lower temperatures only a small amount of acetic anhydride form, and like they say if it is done at lower temperatures mostly ethanol will distill over. So if you simply heated sulfuric acid hot enough and dripped GAA into it, you may collect acetic anhydride vapor?

Today I distilled a bit more and I cooled the distillate till some of it froze, well till all that was gonna anyways. I then poored off the liquid remaining, put it back and of course it hasnt froze yet at -15deg C. I got about 30mls worth
and it floats of top of a salt solution and sinks in water, I think it is at least 50% acetic anhydride, but thats just a stupid guess. it maybe more?

Any ideas on how to determind the conc. of acetic anydride in the GAA?

Perhaps I should figure the density of it, then titrate it with NaOH and see how much it takes to neutrilize it?

edit2: A way one might be able to extract the AA from GAA, is to react it with Fe powder, I know that acetic acid reacts with iron to produce H2(well atleast in solution), and I am pretty sure that the anhydride wouldnt, correct?

[Edited on 17-4-2006 by kclo4]

[Edited on 17-4-2006 by kclo4]

DeAdFX - 21-5-2006 at 17:56

I have a feeling I am pulling a madncrazy....

But is it possible to make acetic anhydride from acetylsalicylic acid, acetic acid and a strong acid? This is the reverse reaction of making acetylsalicylic acid.

AcetylSalicylic acid + acetic acid ----(acid catalyst)--> Salicylic acid + Acetic Anhydride

Is this possible or is this wishful thinking?

[Edited on 22-5-2006 by DeAdFX]

dobka - 26-5-2006 at 07:10

that would never work :]

flyingbanana - 29-7-2006 at 19:11

hmmm...i tried the search engine but couldn't find the answer to my question, which seems too simple to be real

Could plain glacial acetic acid be used for acetylations of relatively reactive sites if some kind of acid catalyst is used and the formed water is distilled off as the reaction progresses?
It wouldn't really form acetic anhydride, but rather the CH3CO-OH2(+) intermediate...yes? no?

[Edited on 30-7-2006 by flyingbanana]

hell-fire - 10-9-2006 at 15:36

IIRC thermal deomposition of sodium persulfate gives sodium pyrosulfate and oxygen. When done in the presence of H2SO4 sodium sulfate and sulfur trioxide is formed.

2Na2S2O8 -> 2Na2S2O7 + O2
Na2S2O7 + H2SO4 -> Na2SO4 + SO3

SO3 is vented in to GAA to give H2SO4 and acetic anhydride. The acetic anhydride is then distilled off at 139C.

CD-ROM-LAUFWERK - 23-9-2006 at 03:56


GAA and AA are soluble in each other, but GAA isn't in chloroform

GAA is 100% miscible whit CHCl3

SO3 is vented in to GAA to give H2SO4 and acetic anhydride.

SO3 is a liquid
if P2O5* cant make AA out of GAA, how could SO3?

*both cold and hot

hell-fire - 27-9-2006 at 23:36

SO3 is a liquid
if P2O5* cant make AA out of GAA, how could SO3?

*both cold and hot

SO3 follows three states depending on the temp, solid, liquid and gas. SO3 reacts with H2O to form H2SO4. 98% GAA has H2O in it, the idea is to change the H2O in to H2SO4 so you're left with a mix of H2SO4 and AA. The AA is then distilled out.

CD-ROM-LAUFWERK - 30-9-2006 at 12:32

i do understand ur idea, but i tell u (again) something:
P2O5 is stronger dehydrating than SO3 (otherwise could P2O5 not dehydrate H2SO4...could it?)
thus if P2O5 cant dehydrate GAA to AA, how comes SO3 could?
u dont realy mean that

Drunkguy - 14-10-2006 at 18:40

The NaOAc/Br2/S looks promising. However I saw that garage chemist has failed when attempting this proc. I had some bromine at one time. I would have wanted to try this if I still had some bromine. I wonder if the S can be replaced with RP?


This suggests that its important to stir the reaction well, and only have the right ratios of starting materials present.

Maybe you can prepare the AcBr in-situ from the acid etc, and then add the appropriate amount of freshly fused NaOAc to this to finish the anhydride proc?

[Edited on 15-10-2006 by Drunkguy]

[Edited on 15-10-2006 by Drunkguy]

[Edited on 15-10-2006 by Drunkguy]

not_important - 14-10-2006 at 22:13

Originally posted by Drunkguy... I wonder if the S can be replaced with RP?


This suggests that its important to stir the reaction well, and only have the right ratios of starting materials present.

You want to make alpha-bromoacetic acid? Then react that with sodium acetate to get CH3-O-CH2-CO2H ?

A slight excess of phosphorus and no excess of Br2 will give the acyl bromide, which does react with MaOAc to form the anhydride.

Drunkguy - 15-10-2006 at 00:46

No, I was showing the mechanism of the HVZ reaction requires a second equivalent of bromine for the rearrangement to take place.

Thus if you just use 1 equivalent of bromine (or perhaps a slight excess of acid), then you should be left with the acyl bromide.

This can then be distilled and reacted with fused NaOAc (perhaps it can also be streamlined, I dont know).

Ofcourse if the SCl2/NaOAc works then brilliant, I was just pointing this stuff out FYI.

Infact the boiling point of AcBr is appreciably lower than AcOH so it would be possible to use a 2 x molar excess prior to distillation.

The only trouble with all this is utilization of bromine and RP creates as many problems as it solves.

[Edited on 15-10-2006 by Drunkguy]

not_important - 15-10-2006 at 01:10

Big difference is that HVZ uses a small amount of phosphorus to make a bit of acyl halide to be alpha-halogenated. Stirring makes sure that all of the acid gets run through the acyl halide and a-halo stages. Making just the acyl halide takes a tiny bit over 1 P : 3 acid ration. Stirring will reduce the amount of now-side-product alpha-halogenation by limited the amount of free halogen, but as the phosphorus is more reactive than the acyl halide, most of the halogen will go into making PX3 and thus acyl halide.

Using prefab PX3 or SX2 avoid the local excess of halogen problen, that would seem to make stirring less critical although hot spots might be a problem without stirring when running larger batches. A slight excess of PX3 or SX2 isn't going to be a problem, as they don't directly perform alpha-halogenation at fairly low temperatures.

garage chemist - 15-10-2006 at 04:05

I have made acetyl chloride from PCl3 and acetic acid. It's important that an excess of acetic acid is used, since PCl3 cannot be separated efficiently from acetyl chloride.

PCl3 could be formed and reacted in situ by passing chlorine into a well-cooled and stirred mixture of GAA and red phosphorus. It must be kept cold to avoid alpha-chlorination of the acetic acid and to make sure that only the red P reacts with the chlorine.
The acetyl chloride can then be distilled off with a column.

not_important - 15-10-2006 at 07:32

Ah, but you don't need to separate the PX3 and AcX. After forming, just add a slight excess of NaOAc, any excess PX3 will react with excess NaOAc to give the anhydride.

S.C. Wack - 18-10-2006 at 14:52

Originally posted by hector2000
this method is not true
no anhydrid will be make

Ber. 9, 444 (1876): "Nach Versuchen der HH.H. Gal und A. Etard kann Essigsäure unter günstigen Umständen durch Phosphorsäureanhydrid in Essigsäureanhydrid umgewandelt werden. Man trägt ziemlich rasch 30 Grm. Phosphorsäureanhydrid in 60 Grm. Essigsäure ein, indem man durch beständiges Schütteln dafür Sorge trägt, dass die beiden Substanzen sich möglichst schnell vermischen. Das Gemenge wird bald braun und erhitzt sich etwas, in diesem Momente destillirt man rasch ab und isolirt das gebildete Essigsäureanhydrid durch die fractionirte Destillation. Die Verfasser haben auf diese Weise ungefähr 3 Grm. der letzteren Verbindung erhalten. Benzoësaure auf ähnliche Weise mit Phosphorsäureanhydrid behandelt liefert eine geringe Menge Benzoësaureanhydrid."

OK so the yield is a little low if true. This is not the same as "no". IIRC Étard killed himself, but not over cries of bullshit on this.

gsd - 19-10-2006 at 09:05

OK. Here is a translation thrown=up by google- translate :((

“After attempts of the HH.H. Gal and A. Etard can be converted acetic acid under favorable circumstances by phosphoric acid anhydride into acetic anhydrid. One carries rather rapidly 30 Grm. Phosphoric acid anhydride in 60 Grm. Acetic acid, by carrying ensuring by steady vibrating that the two substances mix themselves as fast as possible. The mixture soon brown and heats up somewhat, into this moments destillirt one rapidly off and isolirt formed acetic anhydrid by fractionirte distillation. The authors have in this way approximately 3 Grm. receive to the latter connection. Benzoësaure in a similar way treated with phosphoric acid anhydride supplies a small quantity of Benzoësaureanhydrid.”


garage chemist - 19-10-2006 at 15:45

GAA and P2O5 does not make any useable quantities of acetic anhydride. I have tried this several times.
If it is rapidly distilled, nearly pure GAA is the result. If it is boiled for a while before the distillation, a smaller amount of GAA is obtained and the residue is black tar.
I would advise to stop following this route. It is leading nowhere.

The method with bromine + sulfur + sodium acetate (anhydrous) is much more worthwhile to research. I obtained a liquid with higher boiling point than GAA and which dissolved only slowly in cold water. It definately contained some acetic anhydride, judging by its smell (I have pure AA as a reference now).
If you can avoid the runaway that occurs on adding bromine rapidly to a mixture of NaOAc and S, I am sure that you can isolate a useable amount of acetic anhydride.

not_important - 20-10-2006 at 02:51

Bromine is easy to make from a soluble bromide, manganese dioxide, and sulfuric acid; easy to make but does take some care in the handling of. Not a poison so much as a corrosive and thus lung irritant; gas tight systems with absorbent traps at the vents. Working with PCl3 takes similar care. If you are smart in using it, you can recover most of the bromine as bromide from the residue of the reaction, which reduces the effective cost. Just going with spa or pool sodium bromide should give you a quarter Kg of bromine for less than US $20, going by a quick Web search.

There is the ketene route, starting with acetone. Again you're dealing with a unpleasent chemical, well sealed connections and absorbtion traps and good ventilation. It's been discussed here before, the search engine should find the threads. Ketene has the advantage that you don't need acetic acid or acetates, reacting water with ketene generates acetic acid and then acetic anhydride. Plus you can skip the acetic anhydride and just directly acetylate many compounds, aspirin has been made this way. Somewhat wasteful of acetone, glass or metal-working skills are useful.

Magpie - 20-10-2006 at 09:17

Solo has provided us with the Claude Wintner organic chemistry lecture videos. I've watched a few of them, and will watch more. In his lecture on carboxylic acids Claude says that acetic anyhdride can be made from acetic acid, calcium oxide, and heat. This seems too easy to be true. Has anyone else heard of this method?

[Edited on 20-10-2006 by Magpie]

S.C. Wack - 20-10-2006 at 15:16

Of course it is just that easy...with the minor detail of added phosgene or thermal cracking of the acid to ketene and water, etc.

Magpie - 20-10-2006 at 16:13

Claude never mentioned those little details.... I'll have to give this a try once I get my phosgene utility back on line. Thanks for looking into this.

S.C. Wack - 30-10-2006 at 00:40

Originally posted by IPN
Has anyone tested the method in US1926087?

Sort of. A Turkish professor unaware of it was studying the heating of metaphosphate with various salts in the 50's. Halogens were produced in an earlier article by heating the alkali halide salts with metaphosphate; and in this article the good doctor uses the theoretical amounts on a small scale with the halates, nitrite, nitrate, acetate, carbonate, sulfite, oxalate, and chlorides of Al, Mn, Cd, and Ni.

The dry acetate was heated with alkali metaphosphate to 280-370C.
2 CH3COONa + Na2P2O6 --> Na4P2O7 + (CH3CO)2O, or so the author thinks.
The patent used lower heat and GAA mixed in.
The author's name gives no inventor hits at espacenet.
There is nothing in the article that I can see (not speaking cheese-eating surrender monkey is a slight handicap) which suggests that the vapors were condensed and analyzed, which is not surprising given the small scale.

At the end of the article, she seems optimistic that this can be used as a preparative method for acetic anhydride and promises to publish an investigation of this. Later. She died in 1992.

So someone is going to have to try this, and I don't have metaphosphate on hand.

It should be mentioned that except for this and the Pb acetate article that I mentioned earlier, there isn't a whole lot out there on heating acetates and not getting acetone or methane. There are some German patents and some Russian articles on heating Cu, Fe, Ni, Co, Ag, and basic Al acetates alone and getting the anhydride, but AFAIK these all use vacuum.

Attachment: bull_soc_chim_fr_1259_1956.djvu (426kB)
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Drunkguy - 15-11-2006 at 03:54

The article in the quotation is for the Dreyfus procedure. I too liked the look of this but I would think you want to not add the carb. acid through an addition funnel. Rather have a 2 stage set-up:

Sodium metaphosphate at 150C in a rbf with a still-head and condenser attached. Then i'd want to pass the carb. acid vapors into this via a second rbf that is boiling the acid. That way the mixture stays 'moist' or 'saturated' but does not get drenched.

Sodium metaphosphate is readily available btw.

Edit: Actually that idea is quite foolish since the acid vapors would condense en route to the reaction vessel.

There's got to be a better way though such as packing a column with the metaphosphate and condensing the vapors afterwards [but then the column would not be 150C though]

A mechanical stirrer might be a good idea.

Then ultra-sonification tends to help promote various reactions, I like this idea.

[Edited on 15-11-2006 by Drunkguy]

Drunkguy - 30-11-2006 at 09:56

Anybody know if this reaction is feasible:

S2Cl2 + 2RCO2H -> 2RCOCl + SO2 + H2S

If one has really good clean triple distilled sulfur monochloride I see no reason why the product would need to be distilled since the by-products are all gases. Ofcourse its always a good idea to distill it anyway.

Im only interested in the monochloride btw and not SCl2. Partly because the equations are harder to balance, but mainly because SCl2 is scarcer.

[Edited on 30-11-2006 by Drunkguy]

garage chemist - 30-11-2006 at 13:41

With S2Cl2 you don't use GAA (the gases evolved will carry away the volatile acetyl chloride), you use an excess of anhydrous sodium acetate. This way, acetic anhydride is directly formed. The procedure is on rhodium and is possibly the easiest method to make acetic anhydride.

Drunkguy - 30-11-2006 at 14:40

On wiki though this reaction is possible where they use thionyl chloride although the by-products are gases:

H3C-COO-H + O=SCl2 → H3C-COCl + SO2 + H-Cl

The NaO2CR method is all well and good if you want the anhydride, but supposing somebody wants the chloride. Plus since the boiling point of S2Cl2 is >100C surely the more you heat the mixture on distillnig it the greater the chance of carrying over sulfur rubbish into the receiver?

freachem - 7-12-2006 at 11:28

Hi all

Just dabbling here but what would happen if you reacted peroxyacetic acid and acetaldehyde under presure (to reduce CO2 and Methane production ie if this reaction had to happen at all) Water produced would also have to be removed.

[Edited on 7-12-2006 by freachem]

freachem - 7-12-2006 at 22:35

Momentary laps in concentration, I figure more acetic acid will form.

Sauron - 22-12-2006 at 22:50

1. There's an old Russian process from the 40s. Anhydrous sodium acetate (freshly fused and ground) is mixed with sulfuryl bride which itself is made in situ from Br2 and sulfur (maybe I should copy this to the What Can I do with Sulfur? thread.) The mixture is stirred then rotavaped at reduced pressure, the Ac2O is redistilled fractionally at ordinary pressure. The detailed procedure is available online (Rhodium) The snag is that you need liquid bromine.

2. It is well known that Ac2) can be made from acetyl chloride. The problem is that most places where Ac1O is verboten, so is acetyl chloride. Fortunately acetyl chloride is easy to make IF you can get cyanuric chloride (which is cheap) or Oxalyl chloride (which not cheap.) Cyanuric chloride ("CC") is mixed dry with anhydrous sodium acetate and dry-distilled. I believe it is 8 hours at 100C IIRC. Or, simply mix CC with a large excess of acetic acid (glacial of course) and heart to reflux, until no more cyanuric acid precipitates out. That was proposed as a prep method for cyanuric acid a long time ago (c.100 years). Both AcOH and CC are cheap. Acetyl chloride is the side product. Note that 1 mol CC chlorinated three mols AcOH. You must fractionate the Acetyl Chloride from the excess AcOH Then use it to make Ac2O.

A more contemporary procedure uses CC in soln on acetone to chlorinate acetic acid at RT in presence of TEA. Only one Cl on the CC is involved, the hydroxy-CC precipitates out. The yield is about 50% and one is left to work up the acetyl chloride from the TEA and acetone. I'd guess, bubble in some HCl gas, filter off the TEA-hydrochloride solid, then remove the acetone on a rotovap, or fractionate, there's a decent difference in b.p. between acetone and acetyl chloride.

The other procedures are more attractive on a larger scale. The third procedure is good for making acetyl chloride to react in situ to produce an amide or ester for characterization purposes. This procedure was from Tet.Lett and I believe used to be up on the defunct old Hive (pre-Rhodium) board.

Roger Adams in JACS c.1916-1920 wrote up general procedures for making acid anhydrides and alkyl chlorides from the corresponding acids with oxalyl chloride. This is very efficient but costlier than the CC methods because of the molar ratios and the cost of the oxalyl chloride.

I hope this is helpful.

Sauron - 28-12-2006 at 14:01

Here's the article citation for the TCT prep of acetyl chloride from acetic acid in 87% yield, at room temp, 3 hours stirring.

Tetrahedron Letters 40, 4395 (1999)

Same procedure, oxalic acid (anhydrous) to oxalyl chloride 52%

So you can make acetyl chloride and use it to make acetic anhydride by well known methods. (like reacting with anhydrous sodium acetate.)

Or you can make oxalyl chloride and use it to make acetic anhydride directly from acetic acid - the acetyl chloride is formed first then reacts with more oxalyl chloride to give the anhydride.

Best route that I know of.

Sauron - 29-12-2006 at 07:48

Here's the Merck tech data sheet on CC which used to be on their site, they no longer give these away online. There are a number of citations of interest including the one above.

Also the Acros tech data sheet (current) with prices. More citations.

And the Aldrich tech bulletin on oxalyl chloride illustrating numerous reactions and with citations to the literature.

Hope these are useful to some of you.

[Edited on 29-12-2006 by Sauron]

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acetic anhydride peparation

chemrox - 18-1-2007 at 09:43

set up appartus for adding and distilling with a gas capture tube (inverted funnel over water) (hood!)

27 g glacial acetic in the flask; 23 g PCl3 in an addition funnel
keep reaction mixture cool while adding PCl3 slowly
after standing for about 10 min heat gently distilling acetyl chloride as the product add two drops of glacial acetic to product get rid of any PCL3.

Same setup as above, put 30 g of ahydrous NaAc in the flask add 18 ml acetyl chloride in the addition funnel. Add AcCl dropwise to the cooled flask (ice bath). After addition is complete, remove ice bath and heat until no more distillate comes over. Add 2-3 g finely powdered NaAc to the distillate.

yield should be 15-20 g

obviously this can be ramped up as needed.

Notes: NaAc has some water. Fuse in a porcelain dish until no more vapor evolves but avoid overheating

Source: Adams, Johnson & Wilcox, 1963, Lab Exp Org Chem, 5th edition, Macmillan Co.

[Edited on 18-1-2007 by chemrox]

Sauron - 18-1-2007 at 17:05

Cool if and only if you have an abundant cheap source r PCl3 which most everywhere due to Chem Warfare Convention is no longer the case.

Therefore, you must make Acetyl Chloride another way.

See posts above. You can make acetyl chloride (1) from AcOH and CC or (2) you can make either acetyl chloride or Ac2O directly from AcOH and uxalyl chloride.

First reagent is far cheaper, second is more convenient.

Oxalyl chloride you can make from oxalic acid and CC or anhydrous sodium oxalate and CC. CC = cyanuric chloride.

You can buy CC and/or oxalyl chloride in most places without any special restrictions.

Use of a hood is STRONGLY advised.

vulture - 19-1-2007 at 16:05

Why use PCl3 if SOCl2 can get the job done?

Sauron - 19-1-2007 at 22:41

In many places SOCl2 is now simply unavailable.

In Thailand it is flatly prohibited. See Merck Thailand website where they flatly state WE DO NOT IMPORT THIONYL CHLORIDE.

Although possible to make, it is hardly worth the bother when other routes to acid chlorides are at hand. The main utility of SOCl2 is that the byproducts of chlorinating an acid are both gases and this simplifies workup. The same is true of oxalyl chloride. Gases only (CO and CO2).

The most convenient way to make SOCl2 is to pass a mixture of PCl3 and SO2Cl2 through activated carbon under specific conditions. This mixtures disproportionates to POCl3 and SOCl2, which can be fractionated. As SO2Cl2 is readily made by reacting SO2 and Cl2 gases over AC or camphor, effectively this is a facile route to both SOCl2 and POCl3 both of which are useful and now politically incorrect.

The only tricky part is obtaining the required PCl3.

A recent improvement in the catalyst which extends the life of the bed, has the CWC people rather upset.

The prior method of making SOCl2 was oxidation of SCl2, S2Cl2 or a mixture of the two with SO3, or high % oleum, in a pressure reactor, while introducing Cl2 to control side reactions. This would not be such a simple lab scale prep. The sulfur chlorides are available by direct rxn of the elements or more usually on industrial scale as byproduct of manufacture of CCl4 via chlorination of CS2. Again over AC.

The intermediate formed, trichloromethyl sulfenyl chloride, or perchloromethyl mercaptan, is a taxic compound. It is quantitatively reduced by iron filings to CCl4. This is whi CCL4 plants are usually sited alongside CS2 plants.

The perchloromethyl mercaptan can be utilized differently, to produce thiophosgene instead, which is useful in medicinal chemistry. The old method using SnCl2 sucks, and has been supplanted by a catalytic bed to silica gel at about 140 C. By products are molten sulfur and a whole lot of hot angry H2S. The thiophosgene, a toxic liquid, is condensed out by a series of condensers and the H2S ends up in a large caustic scrubber. I believe Akso holds the patents.

learner - 27-1-2007 at 02:32

Could someone clear up for me what the distilation of heating dry asprin is. The asprin turns into a brown liquid that hardens after cooling and a clear strongly acetic smelling liquid that doesn't freeze in a home freezer distills off.
Thank you.

Sauron - 27-1-2007 at 04:49

@CD-ROM LAUFWERK, how did you distill your product? Did you fractionate it?

You haven't reported the bp. That would tell the tale.

The bp of acetic anhydride is quite different from that of acetic acid.

Also if your reaction went as you say you would have some phsphoric acid left in the pot. It is very high boiling.

Acetic anhydride is flammable, acetic acid is not. Try igniting a small sample.

DeAdFX - 16-2-2007 at 09:47

Most interesting.... Methyl Acetate can be converted into acetic anhydride via....

Carbonylation of Methyl Acetate to Acetic Anhydride
The reaction conditions used were similar to those reported for the Eastman Chemical acetic
anhydride process. Into a 300-cc autoclave were added [Rh(dppe)2]+ Cl- (0.46 g), MeOAc (0.695
mol), CH3CHI (0.074 mol), and HOAc (0.29 mol). The contents were pressurized with a 95/5
CO/H2 mix, reacted at 190°C and 750 psi for 4 hours and then analyzed by gas chromatography.
The results are compared with other catalytic runs in Table 3.2.1.

S.C. Wack - 7-3-2007 at 04:33

Someone else looked into the reaction of silver acetate with CS2, but gave a yield figure this time, 45%. Looks like those dudes in 1865 had their shit together, and were smart enough to try the slightly less expensive Pb acetate, too.

From Proc. Chem. Soc. 20, 1957.

A New Synthesis of Carboxylic Acid Anhydrides
By D. Bryce-Smith
(Chemistry Department, The University, Reading, Berks.)

Reactions between silver carboxylates and carbon disulphide appear not to have been described in the literature. Very little reaction occurs when a silver carboxylate, e.g., silver benzoate, is heated under prolonged reflux (46°) with carbon disulphide; but it has been found that at 100—150° reaction is complete within 6—20 hours. The acid anhydride is produced. The overall equation may be written as follows: 2RCO2Ag + CS2 -» (RCO)2O + CO2 + Ag2S. The pure anhydride has been obtained in yields of 98.0, 98.5, 100, and 45% with R = Ph, m-NO2C6H4, p-BrC6H4, and Me, respectively. These reactions are very clean, and the only other organic product in each case has been the free carboxylic acid, probably produced by fortuitous hydrolysis. Since silver carboxylates can be made almost quantitatively from the free adds, the method makes possible a virtually quantitative conversion of acids into anhydrides under neutral conditions. Sodium salts appear to be unsuitable for this reaction.

The following preparation illustrates the method. Silver benzoate (2.90 g.) was heated with dry carbon disulphide (8 ml.) in a sealed tube at 100° for 8 hr. After cooling in solid carbon dioxide-alcohol, the tube was opened. On warming, carbon dioxide (0.18 g.) was evolved. The tube was washed out with dry ether, and the washings were evaporated to give pure benzoic anhydride (1.40 g., 98%), m.p. and mixed m.p. 42—43° without recrystallisation.

It is suggested that the reaction steps in the annexed scheme are involved. This is supported by the observation that carbon tetrahalides also react with silver benzoate, to give benzoic anhydride.

garage chemist - 7-3-2007 at 13:05

I think that the pyrolysis of silver acetate would be a way more attractive route for most members here, which are not able to prepare CS2.
As the pyrolysis of silver acetate yields oxygen besides acetic anhydride, there will also be no need for inert atmosphere.
I think the admin of the german forum got this info from Gmelin, the giant german inorganic chemistry lexicon.

Sauron - 7-3-2007 at 16:51

That's a rather pricey route to Ac2O. Check out the yield per Kg of silver acetate and then go price the silver acetate..

I suppose you can obtain silver metal on the spot market and make your own acetate, the prep doesn't require AR grade. That will get you "some" economy. But the overwhelming % Ag by weight in silver acetate makes this unfavorable.

But I don't see this route being economically competitive with other routes that are available even to chemically challenged EU residents. Setting aside TCT and oxalyl chloride, you ca make acetyl chloride from benzoyl chloride and then react the acetyl chloride with sodium acetate.

S.C. Wack - 8-3-2007 at 00:30

Yeah, silver salts are notoriously unrecoverable and unreducable; and scrap silver has no resale value, certainly not twice as much as it cost as .999 bars 3 years ago. Might as well just pour it down the drain.

I'll take a look in Gmelin's unless someone beats me to it, but I suspect that the statement may deal with this JACS article. Or maybe it's from an article where a 4% yield was obtained under high vacuum, in combination with some exotic catalyst; which is what these quotes always fail to mention. I have a feeling that putting a pile of silver acetate in a flask and distilling will not go well, but who knows.

Edit: Not only is Ag, Pb, Al, Fe etc. acetate heating on the record as possible in some way, mostly impossible as tried, or vaguely possible; the patent numbers have been given, and the journal references have been given. Look them up, present them, translate them, do them, tell us how it goes, or just keep blah blah blah blah blah blah blah blah blah blah blah blah blah. Whatever you do, don't stop blah blah blah blah blah blah blah.

[Edited on 8-3-2007 by S.C. Wack]

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Sauron - 8-3-2007 at 01:07

I used to casually know some people who recovered Ag from photographic emulsions and solutions, mostly from labs that processed medical radiographs (maybe industrial ones too.) I did not pay much attention to their technology.

I did by a large PE tabletop Buchner funnel from them about two feet across and maybe 10" deep (to the frit). Still have it.

Silver cyanide used to be standard for making isonitriles but has been superceded by better methods. Likewise silver fluoride is mostly obsolete for fluorination reactions. And last month when I priced some silver nitrite the price scared me out of that procedure. I have a few hundred g of silver nitrate around here, which I guess I will hoard. Ag salts are to be worked with with OPM (Other People's Money.)

not_important - 8-3-2007 at 01:23

It has been reported that distilling hydrated cupric acetate gives acetic acid and a small percentage of the anhydride with a residue of CuO ( Bamdas & Shemyakin, Zhur. Obshchei Khim. 18, 324-326 1948)

It might prove interesting to try this with the anhydrous acetate. If decent yields of Ac2O were obtained it could be a useful small scale route

CuO + 2 AcOH => Cu(OAc)2 . H2O (OK, actually Cu2(AcO)4 . 2 H2O )

Cu(AcO)2 . H2O ==(100 C, vac)==> Cu(AcO)2 + H2O (g)

Cu(AcO)2 ==(heat)==> CuO + Ac2O

but right now I'm attempting to repair a malfunctioning room heater.

GhostofUnintentionalChaos - 8-3-2007 at 01:41

If you are going to try the copper acetate route, I suggest that you precipitate a Cu(II) salt with an alkali carbonate or an alkali hydroxide. I recommend the first because any significant sized version of the second reaction is exothermic enough to decompose the Cu(OH)2 on the spot to CuO. The (basic) copper carbonate you obtain this way settles out of the reaction mix more nicely than the cupric hydroxide. Either of these dissolve very readily into acetic acid forming a characteristically blue solution (I have a water bottle full of it made with 5% vinegar sitting in front of me now). From personal experience, the extremely weak nature of acetic acid makes the reaction with CuO mind numbingly slow. Some granules I had thrown in vinegar once took several days to dissolve, whereas the basic carbonate will finish up in a few minutes. Just my two cents here. If I had vacuum to dehydrate the acetate, since it is simple enough to make, I would definetly give it a shot.

Sauron - 8-3-2007 at 02:13

Destructively distilling copper acetate is likely a good way to make AcOH with a trace of anhydride. But there's no shortage of AcOH is there?

I understand TCT is hard to buy in Germany or all of Europe. Oxalyl chloride is a little pricey, and for all I know may also be regarded as toxic (perhaps with better justification than in case of TCT.) But, what about benzoyl chloride?

Because that's a prep that can be run on a decent scale, the reagent is cheap, and it works well. The report on this in JACS was by Herbert C.Brown, in his youth. H.C. Brown would later achieve fame worldwide as "Boron" Brown and I doubt there's an organiker anywhere who does not know his story.

not_important - 8-3-2007 at 02:59

Ah, but while distillation of hydrated cupric acetate gives mostly acetic acid, I was speculating on the extension of this to the anhydrous acetate, for which I am unable to prepare a balanced equation that leads to acetic acid.

I would not fell at easy purchasing benzoyl chloride, and have lived in areas where I could not purchase it.

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