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Author: Subject: Acetic anhydride preparation
clearly_not_atara
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[*] posted on 24-5-2023 at 07:30


P2O5 alone was tried and failed extensively. Using calcium chloride as a cofactor is new, though.



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[*] posted on 24-5-2023 at 07:55


Quote: Originally posted by clearly_not_atara  
P2O5 alone was tried and failed extensively. Using calcium chloride as a cofactor is new, though.


The word cofactor is new to me. I looked up what it means and I think I got the concept (organic chemistry isn't my focus). But to make it clear, do you think the simple use of anhydrous calcium chloride and glacial acetic acid is sufficient to produce acetic anhydride? As well as possible anhydrous sodium acetate?

Because if that is the case, I can probably make it quite easily without the need for difficult to obtain and/or very toxic chemicals.
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[*] posted on 24-5-2023 at 08:13


......this might help...solo


Reference Information

https://www.chegg.com/learn/topic/synthesis-of-acetic-anhydr...




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[*] posted on 24-5-2023 at 08:27


CaCl2 alone will not do it. See:

https://pubs.acs.org/doi/pdf/10.1021/ja01852a002




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[*] posted on 24-5-2023 at 08:47


Quote: Originally posted by clearly_not_atara  
CaCl2 alone will not do it. See:

https://pubs.acs.org/doi/pdf/10.1021/ja01852a002


Yes I forgot, sulfuric acid is involved. But that is something I can easily obtain and have extensive experience with. It is no biggie. I will read that pub and edit this response later.
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[*] posted on 24-5-2023 at 10:59


Quote: Originally posted by BAV Chem  
Quote: Originally posted by dicyanin  


GB299342 looks interesting as sodium metaphosphates are commercially available OTC. Sodium hexametaphosphate is a common food additive (E452i) and water softener, and sodium trimetaphosphate is used in construction. Calgon according to some sources is sodium polymetaphosphate Na2[Na4PO3]6 but polycarboxylate to others. Still I've seen 1lb bags of pure sodium hexametaphosphate offered for under 10 euros as a water softener.

The patent from 1927 claims "the production of acetic anhydride from a mixture of sodium metaphosphate, anhydrous sodium acetate, and infusorial earth moistened with glacial acetic acid, the reaction being effected at 150-180°C". Sounds too good to be true, but it could work, and yield wouldn't really be an issue considering the requirements. I've heard mixed results from a similar low-yielding process, heating sodium pyrosulfate with sodium acetate.



That patent (see attachment) also claims that acetic anhydride can be produced by heating a mixture of glacial acetic acid and sodium hexametaphosphate which doesn't work as far as I can tell.

Here's what I did:
127g of anhydrous sodium acetate and 170g of concentrated (~90%) phosphoric acid were thoroughly mixed and refluxed for some hours. I then distilled off the concentrated acetic acid that was formed in the reaction and heated the remaining sodium dihydrogen phosphate to ~700°C in order to convert it into some nice and glassy sodium hexametaphospate. This was broken up and ground to a more or less fine powder. Next all of the hexametaphosphate and acetic acid was refluxed in a round bottom flask for another several hours. During this time the solid really caked to the bottom of the flask (stirring would've helped). Finally I distilled everything to dryness but the vapour temperature never rose above 110°C. Everything I got was some (nearly) glacial acetic acid with a freezing point of 10°C.

Glacial acetic acid should freeze at 16°C
and it's meant to boil at ~120°C.
Acetic anhydride boils at ~140°C.


That doesn't quite mean it can't work at higher temperatures but simply boiling sodium hexametaphosphate in acetic acid doesn't do it. I'm kinda skeptical about the rest of that patent now.



[Edited on 9-4-2023 by BAV Chem]


BAV, I’m not sure if the hexametaphosphate salts would do the trick as described in that patent but metaphosphoric acid would definitely dehydrate GAA to Ac2O, along with most, if not all carboxylic acids to their anhydrides - I can’t find the patent at the moment but o know of at least two old ones from like the early 1900s that mentioned MPA and GAA with some other acyl anhydrides.

I’m not sure if someone else in the thread mentioned it before, but MPA (metaphosphoric acic) is a fantastic dehydrating agent. Magpie demonstrated its ability to generate oleum from 98-% H2SO4 even. You will need a quartz glass setup to run the rxns in though.

The SM thread ‘(HPO3)n Dehydrating agent (polyphosphoric or metaphosphoric acid)’ has some more info and Magpie’s write up is very detailed.
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[*] posted on 24-5-2023 at 16:31


I posted this method for acetic anhydride a little while back, while apparently not seeing this stickied thread. It's probably better placed here than in its own thread.
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...




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[*] posted on 15-8-2023 at 09:29


Quote: Originally posted by dettoo456  
Quote: Originally posted by BAV Chem  
Quote: Originally posted by dicyanin  


GB299342 looks interesting as sodium metaphosphates are commercially available OTC. Sodium hexametaphosphate is a common food additive (E452i) and water softener, and sodium trimetaphosphate is used in construction. Calgon according to some sources is sodium polymetaphosphate Na2[Na4PO3]6 but polycarboxylate to others. Still I've seen 1lb bags of pure sodium hexametaphosphate offered for under 10 euros as a water softener.

The patent from 1927 claims "the production of acetic anhydride from a mixture of sodium metaphosphate, anhydrous sodium acetate, and infusorial earth moistened with glacial acetic acid, the reaction being effected at 150-180°C". Sounds too good to be true, but it could work, and yield wouldn't really be an issue considering the requirements. I've heard mixed results from a similar low-yielding process, heating sodium pyrosulfate with sodium acetate.



That patent (see attachment) also claims that acetic anhydride can be produced by heating a mixture of glacial acetic acid and sodium hexametaphosphate which doesn't work as far as I can tell.

Here's what I did:
127g of anhydrous sodium acetate and 170g of concentrated (~90%) phosphoric acid were thoroughly mixed and refluxed for some hours. I then distilled off the concentrated acetic acid that was formed in the reaction and heated the remaining sodium dihydrogen phosphate to ~700°C in order to convert it into some nice and glassy sodium hexametaphospate. This was broken up and ground to a more or less fine powder. Next all of the hexametaphosphate and acetic acid was refluxed in a round bottom flask for another several hours. During this time the solid really caked to the bottom of the flask (stirring would've helped). Finally I distilled everything to dryness but the vapour temperature never rose above 110°C. Everything I got was some (nearly) glacial acetic acid with a freezing point of 10°C.

Glacial acetic acid should freeze at 16°C
and it's meant to boil at ~120°C.
Acetic anhydride boils at ~140°C.


That doesn't quite mean it can't work at higher temperatures but simply boiling sodium hexametaphosphate in acetic acid doesn't do it. I'm kinda skeptical about the rest of that patent now.



[Edited on 9-4-2023 by BAV Chem]


BAV, I’m not sure if the hexametaphosphate salts would do the trick as described in that patent but metaphosphoric acid would definitely dehydrate GAA to Ac2O, along with most, if not all carboxylic acids to their anhydrides - I can’t find the patent at the moment but o know of at least two old ones from like the early 1900s that mentioned MPA and GAA with some other acyl anhydrides.

I’m not sure if someone else in the thread mentioned it before, but MPA (metaphosphoric acic) is a fantastic dehydrating agent. Magpie demonstrated its ability to generate oleum from 98-% H2SO4 even. You will need a quartz glass setup to run the rxns in though.

The SM thread ‘(HPO3)n Dehydrating agent (polyphosphoric or metaphosphoric acid)’ has some more info and Magpie’s write up is very detailed.


When I read the patent, it seemed to indicate working under pressure to achieve higher temperatures when using the metaphosphate salts and only GAA (middle of page 9). And. In examples 1 and 2, where sodium metaphosphate, sodium acetate, and GAA is used, GAA is "added to the mixture at such speed that [it] appears just moist". Presumably gradual addition of the GAA, as stated in the latter case, would allow for higher reaction temperatures to be achieved at ambient pressure.

It might be worth giving this another shot. I may make an attempt when I have some free time again.
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[*] posted on 15-8-2023 at 12:52


Quote:
BAV, I’m not sure if the hexametaphosphate salts would do the trick as described in that patent but metaphosphoric acid would definitely dehydrate GAA to Ac2O, along with most, if not all carboxylic acids to their anhydrides - I can’t find the patent at the moment but o know of at least two old ones from like the early 1900s that mentioned MPA and GAA with some other acyl anhydrides.

Previous tests reported in this thread by multiple users show that metaphosphoric acid does not produce any isolable AA under any conditions.

Trimetaphosphoric acid H3P3O9 is a superacid at the first deprotonation (pKa < -10) which catalyzes uncontrolled aldol condensation of carboxylic anhydrides. Whether it could be used for benzoic or pivalic anhydrides might be an interesting question; whether it works for AA has been answered with a resounding "no" and also a "why don't people read the thread before posting this crap?".




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[*] posted on 15-8-2023 at 16:54


clearly_not_atara - Apologies for resurrecting a previously disproven route. I've read through this thread casually a few times, but it's a considerable amount of information to retain.

I feel like it would be useful to have a table or some such which lists discussed routes along with whatever conclusions have been drawn for massive threads like this. Problem is, it would take a fair bit of effort, and I'm not sure how much it would help in the end. Adding a section in the wiki, a Google spreadsheet... etc. Aside from the maintenance of such a document, the key would be to have a good way of raising visibility in all parts of the thread in order to prevent cyclical comments.

I'd be interested in any thoughts you might have on this.
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[*] posted on 9-12-2023 at 21:15


Hi.
Just wondering. This online synthesis of Ac2O doesn´t work?
Anhydrous sodium acetate, dropping acetyl chloride, kept protected from moisture with calcium chloride tube.. than distilled 2x. of course there is more to do, this but this is the base.
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[*] posted on 9-2-2024 at 08:18


I just don't think it's considered interesting. Mostly we're interested in preparing acetic anhydride without the use of the strong dehydrating reagents that require hazmat shipping and attract regulatory scrutiny.

But like the bromine thread, this one has mostly been "solved" by the acetonitrile + HCl method and/or the benzoic acid thermal dehydration (260 C) with catalytic phthalic acid (to benzoic anhydride, therefrom to Ac2O). The remaining interest is further simplifying those methods, like maybe you can use TsOH + NaCl in MeCN + AcOH instead of gassing. Maybe diglycolic acid or adipic acid is easier to use than phthalic. Etc.

EDIT: not adipic, unfortunately: https://pubs.rsc.org/en/content/articlelanding/1927/jr/jr927...

[Edited on 9-2-2024 by clearly_not_atara]




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[*] posted on 9-2-2024 at 10:17


Quote: Originally posted by clearly_not_atara  
I just don't think it's considered interesting. Mostly we're interested in preparing acetic anhydride without the use of the strong dehydrating reagents that require hazmat shipping and attract regulatory scrutiny.


I’m not sure why the SCl route isn't more used. Sure it needs synthesising SCl, but that’s not such a hassle.
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[*] posted on 9-2-2024 at 14:22


S2Cl2 is not so bad itself, but it's infamous for ruining any container you keep it in. So you probably want to use it all quickly after you make it. But that's difficult for the on-again, off-again work most of us do.



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[*] posted on 10-2-2024 at 09:06


Quote: Originally posted by clearly_not_atara  
I just don't think it's considered interesting. Mostly we're interested in preparing acetic anhydride without the use of the strong dehydrating reagents that require hazmat shipping and attract regulatory scrutiny.

But like the bromine thread, this one has mostly been "solved" by the acetonitrile + HCl method and/or the benzoic acid thermal dehydration (260 C) with catalytic phthalic acid (to benzoic anhydride, therefrom to Ac2O). The remaining interest is further simplifying those methods, like maybe you can use TsOH + NaCl in MeCN + AcOH instead of gassing. Maybe diglycolic acid or adipic acid is easier to use than phthalic. Etc.

EDIT: not adipic, unfortunately: https://pubs.rsc.org/en/content/articlelanding/1927/jr/jr927...

[Edited on 9-2-2024 by clearly_not_atara]


clearlynotatara,

Has the benzoic acid dehydration with phthalic anhydride been discussed on this forum before? I tried to find it using Google to no avail.

That would be interesting because you can recycle the phthalic acid.

[Edited on 10-2-2024 by Loptr]




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[*] posted on 10-2-2024 at 17:30


Loptr: It was discussed on the previous page. In order to better keep track of the enormous amount of information in this thread, I have updated the Wiki articles:

http://www.sciencemadness.org/smwiki/index.php/Organic_acid_...

http://www.sciencemadness.org/smwiki/index.php/Acyl_chloride

Perhaps the article "organic acid anhydride" should be moved to "carboxylic anhydride" in order to distinguish it from other anhydrides such as the sulfonic anhydrides, which are prepared differently.

Attached is the reference describing the preparation of acetic anhydride in excellent yields by pyrolysis of silver acetate at 380-400 C in an argon atmosphere. This reaction is widely discussed but poorly understood.

Attachment: kirshenbaum1953.pdf (667kB)
This file has been downloaded 132 times





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[*] posted on 11-2-2024 at 22:21


I can't edit that post anymore, but I wanted to add that in the absence of phthalic acid, a high-boiling dicarboxylic acid can probably be obtained by the Diels-Alder cyclocondensation of itaconic anhydride, formed by pyrolysis of citric acid, with alpha-phellandrene, found in dill essential oil. I think this is a simpler than trying to oxidize naphthalene or naproxen. Dill oil is surprisingly popular among the hippies and is about 1/3 alpha-phellandrene; the other components probably won't interfere with the cyclization.



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[*] posted on 15-2-2024 at 11:02


Reference Information



Base-Mediated Synthesis of Anhydrides from Activated Amides
Iliyasu Aliyu Bashir and Sunwoo Lee
J. Org. Chem.
2023, 88, 9, 6159–6167
doi:10.1021/acs.joc.2c03098




ABSTRACT:
Symmetrical anhydrides were synthesized from activated amides such as N-benzoylsaccharins and N-Boc-protected benzamides. The activated amides reacted with H2O in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) at 25 °C to produce the corresponding symmetrical anhydrides in high yields through C−N bond cleavage. In addition, N-benzoylsaccharins reacted with benzoic acid derivatives to generate unsymmetrical anhydrides in high yields.

...posted by fcttc from hyperlab


Attachment: Base-Mediated Synthesis of Anhydrides from Activated Amides.pdf (1.7MB)
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[*] posted on 22-5-2024 at 10:11


Has anyone on here had any success with the reaction of phosphorus pentoxide and glacial acetic acid?
I know its rare in some countries but I have some phosphorus pentoxide and I gave it a go using that one suspicious paper that everyone refers to where they also make it from calcium chloride "apparently".

Handling the phosphorous pentoxide is a pain, even just transferring it straight from a sealed jar as quickly as possible with a spatula in small portions to the reaction mix was a whole ordeal. Water is so in l9ve with it that it jumps onto it faster then you spell tar.. And indeed tar was the result even with an ice bath under the round-bottom with stirring and the fastest spatula transfer skills which I am sure made a world record.

Regardless, the mixture was refluxed and attempted distillation which just yield unreacted acetic acid and this time tar with some added foaming bubbles.

Does this whole setup have to be run in a dry box and then refluxed with a drying tube on top the of the condenser?

I have an exotic synthesis I've been wanting to attempt for a long time now and have acquired 11 out of 12 reagents with the only thing standing in my way being acetic anhydride:mad:

Any help greatly appreciated :)

[Edited on 22-5-2024 by greenlight]




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[*] posted on 23-5-2024 at 05:48


Quote: Originally posted by greenlight  
Has anyone on here had any success with the reaction of phosphorus pentoxide and glacial acetic acid?

No, but around three million people (including you) have failed. My interpretation is that phosphoric anhydride polymerizes Ac2O faster than it dehydrates AcOH.

There is a paper out there about the rxn of P2O5 with CaCl2 giving POCl3 under some conditions: you could just do that and then use POCl3 as normal.




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[*] posted on 23-5-2024 at 06:27


If someone needs the Ac2O for a simple friedel crafts (or some other carboxylic anhydride for that purpose), then PPA + GAA (or PPA + dry propionic, butyric, etc) should work fine on its own. Or, if the Ac2O is to be used for nitrations, just dehydrate WFNA with PPA to N2O5.

I have not seen any instance of amine protection with GAA + PPA though.

Other than that, you will need at least POCl3 like atara said.
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[*] posted on 23-5-2024 at 11:42


Quote: Originally posted by clearly_not_atara  

No, but around three million people (including you) have failed. My interpretation is that phosphoric anhydride polymerizes Ac2O faster than it dehydrates AcOH.


I’ll try that using DMSO as a solvent. Maybe it can work?
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[*] posted on 23-5-2024 at 14:01


Quote: Originally posted by Keras  
Quote: Originally posted by clearly_not_atara  

No, but around three million people (including you) have failed. My interpretation is that phosphoric anhydride polymerizes Ac2O faster than it dehydrates AcOH.


I’ll try that using DMSO as a solvent. Maybe it can work?

Did you mean to quote the other part of the post? I have attached the paper. It appears that the reaction with NaCl actually begins at a lower temperature (250 C) than with CaCl2 (400 C). This is the opposite of what I would have expected. I think I only read the abstract when I found it the first time. But CaCl2 will have a better solubility in organic solvents. LiCl may be worth considering.

I think P2O5 might form an adduct with DMSO similar to the SO3 adduct. Possibly a less nucleophilic solvent would be good. The bp of propylene carbonate (240 C) is close to the rxn temperature for P2O5 + NaCl found by Tarbutton et al, though I have no idea if the solvent would be stable under reflux with these reagents present.

Attachment: tarbutton1941.pdf (799kB)
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[*] posted on 26-5-2024 at 09:58


Thankyou for the replies,
Would it be possible to run the reaction by slowly dripping glacial acetic acid into phosphorus pentoxide which is suspended in dry dichloromethane with stirring?
Phosphorus pentoxide is not soluble in DCM and the glacial acetic acid is miscible as well as acetic anhydride and if it ran successfully the AA could be distilled off afterwards.
The only problem is the maximum temperature that can be achieved is low due to DCM's boiling point ~38°C.

Maybe hexane could work otherwise?

As long as the solvent is not an alcohol and doesn't react with the P2O5 or acetic acid would this be viable as it also keeps the P2O5 from reacting with moisture in the air in the flask and during addition like in the original method.

I am probably overlooking something crucial here as it is late at night but the idea just came to me.


[Edited on 26-5-2024 by greenlight]




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[*] posted on 26-5-2024 at 13:51


Quote: Originally posted by greenlight  
Thankyou for the replies,
Would it be possible to run the reaction by slowly dripping glacial acetic acid into phosphorus pentoxide which is suspended in dry dichloromethane with stirring?
Phosphorus pentoxide is not soluble in DCM and the glacial acetic acid is miscible as well as acetic anhydride and if it ran successfully the AA could be distilled off afterwards.

I was contemplating trying something like that until I realised that the theoretical maximum yield from all 100g of the P2O5 I had on-hand, was approximately frig-all squared.
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