Acetic Acid ------> Acetic Anhydride -archive file

[megalomania]

Detonator
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posted February 17, 2001 02:25 AM
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Can you obtain Acetic Anhydride from Acetic Acid or vice versa??


Anthony
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posted February 17, 2001 12:34 PM
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Yes, you can synthesise acetic anhydride from acetic acid.
Why would you want to make acetic acid from acetic anhydride?


PYRO500
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posted February 17, 2001 04:22 PM
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just add water


ALENGOSVIG1
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posted February 17, 2001 05:11 PM
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Moving to misc.
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Detonator
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posted February 18, 2001 01:19 AM
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How would you synthesis acetic anhydride from acetic acid?


kv21
A new voice
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From: Berlin
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posted February 18, 2001 01:50 PM
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Preparation of acetic anhydride and acetyl chloride
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Acetyl Chloride
===============

Connect a dry 250 ml three neck flask with a distillation adapter,
condenser and addition funnel. Use a 250 ml rb flask for the receiver
connected to the condenser with a vacuum adapter. Use the vacuum adapter
to make a gas trap with rubber tubing to an anhydrous CaCl2 drying tube
exiting to an inverted funnel suspended over a beaker of water. This
important stage is to protect the distillate from water while absorbing HCl
evolved in the reaction.

Place 54 g. (52 ml.) of glacial acetic acid in the three neck flask, close
with a stopper and add slowly through the addition funnel 46 g. (29 ml.)
of phosphorus trichloride. Cool the flask by immersion in a water bath. Mix
the reactants thorougly and, after allowing the mixture to stand for ten
minutes, heat the water bath to 40-50? and maintain it at this temperature
for thirty minutes, with occasional swirling of the flask. During the
heating the liquid usually separates into two layers. Acetyl chloride forms
the upper layer.

Distill the acetyl chloride by heating the water bath to boiling and
maintaining it at that temperature as long as any liquid passes over. Cool
the receiver in an ice bath during the distillation. The syrupy residue in
the distilling flask is phosphorous acid, which is discarded.

--> CAUTION: The reaction mixture must not be overheated since this will
lead to formation of phosphine, which is spontaneously flammable in contact
with air.

To the distillate add two drops of glacial acetic acid, to destroy mixed
phosphorous-acetic anhydrides that would cause turbidity to develop on
standing. Redistill the acetyl chloride from a distillation apparatus
arranged as before except without the addition funnel and with a
thermometer. Collect separately in a dry receiver the portion boiling at
50-56? and transfer it to a dry weighed glass-stoppered bottle. Acetyl
chloride attacks corks and rubber stoppers. The yield is 44-56 g.

Acetic Anhydride
================

The apparatus for this process is similar to that used for the preparation
of acetyl chloride. The same precautions for exclusion of moisture must be
observed but it is unnecessary to provide the inverted funnel arrangement,
since hydrogen chloride is not evolved.

In a 250ml. rb flask fitted as for making acetyl chloride, place 60 g. of
finely pulverized anhydrous sodium acetate.* Arrange in place the
condenser, dry receiving flask and drying tube; the receiver need not be
cooled. Check to insure that all connections are tight. Cool the reaction
flask in a bath of cold water and add dropwise, through the addition
funnel, 40 g. (36 ml.) of acetyl chloride.

After the addition has been completed, remove the water bath and shake the
flask to obtain good mixing of the reactants. Recheck the connections for
tightness.

Dry the outside of the flask with a towel and heat it with a mantle or oil
bath. Continue the heating until no more distillate comes over but do not
overheat the solid residue.

To the distillate add 4-6 g. of finely powdered anhydrous sodium acetate,
to react with a small amount of acetyl chloride that may be present. Add a
boiling chip and redistill the crude acetic anhydride. Collect the product
distilling at 132-138? in a dry flask. The yield is 30-40 g.

* NB: Commercial anhydrous sodium acetate usually contains some moisture.
To remove moisture fuse 70-80 g. in a casserole and stir until no
more water is evolved. Do not overheat! Cool and quickly pulverize.
Store in a tightly sealed container before use.


Detonator
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posted February 19, 2001 01:23 AM
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Thanks guyes, but how to obtain it from Acetic Acid????????????????????????????


Jhonbus
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posted February 19, 2001 10:31 AM
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From the KIPE2:
Acetic anhydride is produced by absorption of ketane vapors in
acetic acid. Acetone is injected into a chrome/iron alloy pipe through one
end equipped with a feed valve and assembly. This pipe is previously purged
with argon or nitrogen. The pipe is heated to 650 to 670 degrees C. This
heating can be done by electric heat with a thermostat or by a coal or gas
fired oven. The injection of acetone into the reaction tube is begun when
the proper temperature is reached. The other end of the pipe is attached
to a stainless steel 3/8" tubing. This tubing is placed through a two hole
stopper in a gallon jar placed in a salted ice bath. This is to collect all
unreacted acetone. In the other hole in the stopper on this bottle is
placed a second stainless steel tubing. This goes to another gallon jar
through a two hole stopper. In this jar is placed the acetic acid. The
second hole in this stopper is placed in line for venting purposes. This
line is placed outside or in a safe place for the poisonous fumes to go.
Acetone is injected slowly into the chrome/iron pipe @ 650 to 670
degrees C. This will react approximately 15-25% of the acetone into
ketane. The vapors from the reactor [are] directed into the first bottle. The
unreacted acetone will collect here. The ketane vapor will continue through
the tubing to the next jar. The ketane vapors are absorbed here by the
glacial acetic acid. These vapors are absorbed until the density of the
liquid is 1.08 @ 20 degrees C. This is checked by a hydrometer placed in
the glacial acetic acid. At the time this specific gravity is reached the
material in the second jar is acetic anhydride.

...CAUTION: Acetone is highly flammable. Great care is needed to
ensure total absence of [oxygen] in the reactor prior to injection of acetone.
Failure to do this can result in an explosion. The whole reaction should be
done with very good ventilation. (don't breathe the ketane!)

[This message has been edited by Jhonbus (edited February 19, 2001).]


Scarecrow
A new voice
Posts: 7
From:
Registered: FEB 2001
posted February 19, 2001 11:29 AM
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1) That sounds as a very difficult process to make and one needs some equipemment to make it work!
2) Could you make a diagram for this!!
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Jhonbus
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posted February 19, 2001 11:54 AM
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Here's a lovely picture:
<img src="http://www.geocities.com/jhon_bus/Ethanhyd.jpg" alt=" - " />
You would want to purge the whole apparatus with argon or similar before use.


Detonator
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Registered: NOV 2000
posted February 20, 2001 01:37 AM
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I think it's very hard to be done without a lab!!!!
Don't you think so?


ALENGOSVIG1
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Posts: 766
From: Vancouver, Canada
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posted February 20, 2001 02:21 AM
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No, i dont beleive that would be difficult. Unless you cant get jars tubings ans ome pipe. Otherwise i beleive it is wuitw feasible.
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Anthony
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From: England
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posted February 20, 2001 10:53 AM
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The problem I can see is keeping the pipe heated to within the rather narrow window of 20*C at such high temperatures. Maybe it could be done with a furnance with fine thermostat control, but it's not something you could do with a blow torch (unless you had a good high temerature sensor).
I take it the system is pressurised by the heating of the acetone expanding into ketane gas. This would require an actual one-way valve assembly on the heating pipe, you may find it difficult to find valves that will withstand that kind of temperature.

Shame you can't get bottled ketane

[Marvin]

H2C=C=O is Ketene, not ketane.

Its extremely toxic, comparable to phosgene, you really do not want to make this with leaky aperatus but at least you wont miss the smell of this stuff, so you know if its killing you.

Its very reactive, reacts with itself if left alone, which is doubtless why you cant get it in tanks. There is an acceptable synth in organic synthesis, which now its online is here,

<a href="http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?rxntypeid=292&prep=CV1P0330" target="_blank">http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?rxntypeid=292&prep=CV1P0330</a>

Ive been told there are improvements to the synthesis made after this was put together that involve a copper catalyst instead of porcelain, its worth looking these up if you plan to try this.

[Dave Angel]

I've just done a run of the ketene process with the apparatus used in this (http://www.roguesci.org/theforum/showthread.php?p=61896) thread. The only difference being that a litre flask with 800mL of AcOH and the Dreschel head was placed before a simple gas drying bottle with more AcOH. I'll have to put things on hold for a while though, as one of the ground glass joints I fitted to the copper tube has cracked quite badly and may need to be replaced.

I found that the rate at which the acetone distills over is really quite important. Initially it came over too quickly and some even got beyond the reflux condenser (see below). The heated section of pipe could not be maintained at a red hot temperature and no ketene was formed. The rate at which the acetone came over was lowered and the pipe began to glow red hot. Some suck back occured temporarily until significant ketene began to form.

I had almost finished the run when the crack occured in the glass and I had to stop it. About 800mL of the 1L of acetone had been distilled across, that which had not been pyrolysed had condensed and had a yellow colour to it. The total acetone left over after combining the condensate and that not distilled was 800mL.

The density of the AcOH in the main flask had gone from 1.05g/mL to 1.04g/mL. I'm concerned that no acetic anhydride was formed and this density change is due to the acetone which got into the acetic acid. Perhaps some Ac2O was formed and the decrease in density caused by the acetone was limited by this. I have also thought that Ac2O, density 1.08g/mL mixed with 1.05g/L AcOH may result in a lowering of density, in a similar way to how some mixed compounds have melting points lower than either alone. I would certainly appreciate any information anyone has on this matter.

There is one ray of hope: I saw a slight fuming effect, characteristic of Ac2O, occur as I poured the 'product' into a measuring cylinder to take a density reading.

[Microtek]

I think the best way of testing the purity of it would be via titration. Pure Ac2O consumes 17.7 % more alkali per gram than AcOH so it would require some accurate equipment or a large sample.

[Dave Angel]

Nice one Microtek, I have a burette so the procedure is not a problem, it's this unknown quantity of acetone contaminant that is. I've repaired the apparatus but it's less than perfect and if it still leaks then I'll have to rethink.

I'll try another run today (providing I have any burner fuel left) and see if I can affect the density again, without further acetone contamination. Anymore Ac2O formed should help overcome the acetone dilution and, if necessary, a subsequent titration compared with acetic acid alone will hopefully give the desired result.

[Marvin]

Is fractionally distilling the products not an option? This would determine the amounts directly, and non destructivly.

Id suggest adding ammonia, but I cant think of a way offhand to seperate ammonium acetate from acetamide.

I have to say also, I like some of the methods apearing at sciencemadness for acetic anhydride. One method uses sodium pyrosulphate which is extremly cunning.

[Dave Angel]

I could try fractional distillation, I built a column out of an old condenser and broken glass which isn't perfect but functions, though I don't have a way of fitting a thermometer to this suitably.

My burners are just about out of fuel so I'm not going to be doing any more runs for the time being. I was thinking that pumping more ketene through the AcOH would be the way to go as I would get more product with my time as well as confirmation of product forming.

Thanks for the reference to sciencemadness. The pyrosulphate process looks interesting and I might give it a try once I have the reagents. I notice it was also suggested there that CO2 could be bubbled through alcoholic sodium acetate solution to yield Ac2O and Na2CO3. It was also noted, however, that the anhydride would go on to react with the alcohol.

Perhaps if acetone is inert towards Ac2O and will dissolve sodium acetate then one could make the acetate from vinegar, and bubble welding CO2 through it. It sounds too good to be true but is certainly worth investigating, as it is the simplest of all the processes I have read about, would save money and make Ac2O a cheap OTC synthesis.

[Edit] I've just done a few tests and sodium acetate is not soluble in acetone. It will dissolve in glacial acetic acid, although this is not OTC and would react with the CO2 to give carbonic acid as a byproduct which would then decompose to water (as noted on the sciencemadness forum), bad for acetic anhydride. One could use pure acetic acid but this would only enhance the amount of carbonic acid produced.

In a closed system I expect some kind of equilibrium would exist as the water from the carbonic acid decomposition would turn the anhydride back into acetic acid, but more CO2 would also be produced and react with the acetic acid...

I wonder if the addition of anhydrous MgSO4, CaCl2 or CuSO4 to the mix would affect the main reaction at all, as these could possibly serve to pick up any water formed and prevent it from destroying the Ac2O. This would force the equilibrium to decompose more carbonic acid but the water would be removed and the extra carbon dioxide formed, without the presence of the water, would force the equilibrium of the main reaction towards the anhydride side

I really don't see an alcohol as an option for the solvent due to the esterification problem. I can't think of any other solvents which would be suitable except for a couple of polar aprotics: DMF and DMSO, and they aren't exactly easily available.

Also, whilst I was thinking of closed systems and dissolved CO2, I thought that perhaps a Soda Stream fizzy drinks maker could be used to add the CO2 to the solution. After all these are designed to dissolve the gas in liquid, rather than just pass it though.

Finally, I sketched out a possible mechanism for the reaction of CO2 with AcOH to form Ac2O, it still needs transferring to the computer, though I expect it's of limited interest to most members, and those who are interested are probably capable of working it out for themselves anyway! It looked reasonable to me, despite the fact that I've never drawn a mechanism detailing the formation of a carbonate anion before :)

[Dave Angel]

Things are not going well so far I'm afraid. I've repeated my ketene experiment with the same acetic acid and there was not the slightest increase in density, tested using a hydrometer accurate to 0.002 g/mL in the range of 1.0 to 1.1g/mL. I wonder if the temperature is too high and all the ketene is decomposing, or perhaps the path after the reflux condenser to the bottle of acetic acid is too long and the ketene is breaking down, (I think it's polypropylene or polyethylene tubing a foot or so long). Something flammable (methane?) is definitely getting beyond the condenser as plenty of gas was burning off at the output.

I've also tried the proposed CO2 method, although I'm rather sceptical about it, I can't find any reference to it in patents or web searches. Approx. 800mL of GAA was placed in a Soda Stream bottle with 200g of anhydrous MgSO4. CO2 was added multiple times over a period of 2 hours, and the bottle was disconnected several times and gently shaken to mix the contents. After about 2 hours the GAA began to freeze so it was clear that no transformation was taking place, at least not on a large enough scale to alter the freezing point. After filtration, density had remained at 1.05g/mL. Perhaps (if this works at all), it must be done with sodium acetate in aqueous solution. Maybe the formation of large amounts of carbonic acid is critical to the reaction. I may attempt this at a later date. Nothing much wasted though as both the AcOH and MgSO4 were recovered.

I've kept most of the potassium hydrogen sulphate from nitric acid distillations as I thought it may be useful one day. Conversion of this to the pyrosulphate is also on my to do list, though I've seen some interesting, however more complex ways of making it on sciencemadness too.

I believe there is also a route involving acetaldehyde, which I have not looked into fully yet. I hope to make significant quantities of acetaldehyde soon which should open up this experimental path.

[nbk2000]

Anything madscientist says over at the sciencemadness forum must be taken with a bucket of salt, as his chemistry skills are...how to say this politely...erm...LAME?!

Yes, indeed, very lame.

[Sarevok]

Instead of using ketene + acetic acid method, or acetic acid + phosphorus trichloride (PCl3) method, one can use POCl3 (I already said how to make it, search - that method probably works) and sodium acetate (buy it or make it from vinegar and lye) to make acetyl chloride (see A text-book of practical organic chemistry, on polverone's site), and then use acetyl chloride and sodium acetate to make acetic anhydride (see the same book, or kv21's post). Only a distillation apparatus and some simple stuff would be required.

[Dave Angel]

Heh, speaking of buckets of salt, I made plenty of sodium acetate yesterday with the intention of using it for the CO2 and the sodium pyrosulphate processes. If anyone else makes some, I recommend crushing it up and washing with acetone in a Buchner funnel as this makes much of the sodium acetate into fine, dry sugar-like crystals which can be sieved out.

I've also done a few experiments in trying to make the pyrosulphate and temperature control is certainly an issue. Fortunately, in the first bit of luck I've had this week, my hotplate set to max seems to produce the perfect temperature for conversion of the potassium hydrogen sulphate to pyrosulphate without a great deal of decomposition. The hydrogen sulphate melts and takes on a yellow appearance, and water begins to come off. I hope the same goes for the sodium hydrogen sulphate as this is more readily available. Despite the potassium salt being a by-product, I don't make quite enough of it on a regular basis to facilitate a decent scale of acetic anhydride production, should the whole process be a success.

Now that you mention it Sarevok, I remember my organic lecturers speaking of POCl3 or 'poccle three' as they said it. Vogel looks a very interesting read, I've just skimmed through it so far, and I particularly like his ketene apparatus. Making and using POCl3 for acetyl chloride, and then making acetic anhydride looks useful too, however the route is a rather long one in comparison to the pyrosulphate one. Still, knowing how to make acetyl chloride from easy to obtain reagents is handy, so thanks.

[Sarevok]

For those who are concerned, the sodium pyrosulphate method, mentioned by dave, is described here (http://l2.espacenet.com/espacenet/bnsviewer?CY=gb&LG=en&DB=EPD&PN=GB424573&ID=GB++++424573A++I+).

[Dave Angel]

I've just finished an experiment with potassium pyrosulphate. 130g of crude K2S2O7 was crushed into a fine powder and mixed intimately with 60g of the fine sodium acetate I made the other day. Such a large molar excess of the pyrosulphate was used as I am unsure of the actual percentage composition of the mix of sulphates, bound to have been formed.

The mixture, already beginning to cake due to moisture and perhaps some Ac2O formation, was placed in a round bottomed flask and wetted with a small quantity of glacial acetic acid. This was refluxed for approximately 2 hours and the resulting liquid was distilled with the recieving flask being a quick-fit separating funnel. 8 fractions of between 14mL and 25mL were tapped off and rough calculations of density made using their volumes and masses, indicating densities of around 1.07g/mL.

The following fractions were combined such that the volumes were large enough to make the associated hydrometer readings:

3+4 - 1.068g/mL
5+6 - 1.066g/mL
7+8 - 1.062g/mL

Quite pleasing results for such a simple process. What is interesting is that the density actually decreases as the distillation proceeds, the opposite of which would be expected, due to the lower bp. of the acetic acid. I wonder if any unconverted KHSO4 may have decomposed releasing water as the distillation proceeded and the temperature increased, thus lowering the density of later fractions.

A simple oxidation of methylated spirits should provide a decent amount of acetic acid. NaOH and NaHSO4 being the other reagents necessary, makes this process totally OTC as well as simple.

One can recycle the mix of acetic anhydride and acetic acid produced in the first run to wet the reagents in subsequent runs gradually diluting the acetic acid in the newly forming acetic anhydride. Fractional distillation should also help to purify the product, once a quantity worth processing is made, the acetic acid being recycled into sodium acetate.

[Hinckleyforpresident]

I read that it MIGHT be possible to make acetic anhydride with sulfuric acid and anhydrous magnesium sulfate. Has anybody tried this? Or is this method completely wrong?

[nbk2000]

Do you mean using vinegar or glacial acetic acid as a starting base?

Because if all you have to work with is sulphuric acid and magnesium sulfate, no acetic acid (of any concentration), than you're not going to get acetic anything out of that.

[Hinckleyforpresident]

Sorry for the lack of information.

I meant distilling glacial acetic acid with sulfuric acid and anhydrous magnesium sulfate.

Here is the reaction: 2CH3COOH + H2SO4 + MgSO4 -> CH3(CO)O(CO)CH3 + H2SO4 + MgSO4.H2O

[Enkidu]

I couldn't tell you for sure whether or not it will work; that being said, I seriously doubt that you will have any success with that method. Anhydrides are much more difficult to synthesize than ethers or esters, and, IIRC, no one has had much success trying to dehydrate acetic acid to acetic anhydride.

Where did you see this process? A patent? A post somewhere else? Do tell.

[Hinckleyforpresident]

It's from sciencemadness. They also doubted it work well. I figured it's worth asking and maybe trying because if it did in fact work then we would have OTC acetic anhydride.

[nbk2000]

Sulphuric would carbonize the organic acetic molecule, making it non-acetic. ;)

The only reasonably effective way of making acetic anhydride is a ketene lamp.

[Hinckleyforpresident]

Any hope of that generator drawing nbk?

[nbk2000]

Vogel has a rather descriptive diagram of the setup and explanation on page 373.

http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p0679

[Hinckleyforpresident]

I'm getting a 403 denial message when I click the link.

[megalomania]

That method may work, but the yield would be dreadfully poor I would think. If that method was at all feasible, then the good people at the Hive would have stocked up on salad dressing and epsom salts years ago.

EDIT:
The ? in the link is causing the redirector to throw fits. You can't copy and paste the link either... Copy and paste within the code tags now.

[nbk2000]

I had it in code tags to start with, but it parsed as a link, but the code tags were still there when I went to edit it, and now it's showing in code? :confused:

Anyways, it's working now.

[tranquillity]

From wikipedia and the reference: "Eastman Chemical Company Acetic Anhydride Process" Catalysis Today (1992), volume 13, pp.73-91
***
Acetic anhydride is produced by carbonylation of methyl acetate:

CH3CO2CH3 + CO → (CH3CO)2O

This process involves the conversion of methyl acetate to methyl iodide and an acetate salt. Carbonylation of the methyl iodide in turn affords acetyl iodide, which reacts with acetate salts or acetic acid to give the product. Rhodium and lithium iodides are employed as catalysts. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions. In contrast, the Monsanto acetic acid synthesis, which also involves a rhodium catalyzed carbonylation of methyl iodide, is at least partially aqueous.
***

I suppose there would be a substitute for the rhodium salt that is more easily accessible. Everything else is quite easy from a decent lab setup.

The reactions as I see it:
CH3OH + CH3COOH + H2SO4 --> CH3COOCH3 + H2SO4.H2O

CH3COOCH3 + NaI --> CH3I + NaCOCH3 (CH3I Distills off at 42.43 °C)

CH3I + CO --> CH3COI (I assume this is where the catalyst is needed)
Not too sure about the specific reaction conditions someone could fill in the blanks if they have the article.

CH3COI + NaCOCH3 --> NaI + (CH3CO)2O