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Author: Subject: Acetic anhydride preparation
garage chemist
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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]

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kclo4
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"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
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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.

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kclo4
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"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?

edit:
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]

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Mood: @%&$ing hardcore baby 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 Harmless Posts: 3 Registered: 26-5-2006 Member Is Offline Mood: No Mood that would never work :] flyingbanana Harmless Posts: 38 Registered: 1-3-2005 Member Is Offline Mood: No Mood 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 Harmless Posts: 5 Registered: 10-9-2006 Member Is Offline Mood: Unstable. 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 Harmless Posts: 30 Registered: 23-4-2005 Member Is Offline Mood: No Mood  Quote: GAA and AA are soluble in each other, but GAA isn't in chloroform GAA is 100% miscible whit CHCl3  Quote: 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 Harmless Posts: 5 Registered: 10-9-2006 Member Is Offline Mood: Unstable.  Quote: 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 Harmless Posts: 30 Registered: 23-4-2005 Member Is Offline Mood: No Mood 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 Hazard to Others Posts: 172 Registered: 23-12-2005 Member Is Offline Mood: somewhat pissed. 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? hell-volhard-zelinsky-reaction 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 International Hazard Posts: 3873 Registered: 21-7-2006 Member Is Offline Mood: No Mood  Quote: Originally posted by Drunkguy... I wonder if the S can be replaced with RP? hell-volhard-zelinsky-reaction 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 Hazard to Others Posts: 172 Registered: 23-12-2005 Member Is Offline Mood: somewhat pissed. 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 International Hazard Posts: 3873 Registered: 21-7-2006 Member Is Offline Mood: No Mood 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 chemical wizard Posts: 1803 Registered: 16-8-2004 Location: Germany Member Is Offline Mood: No Mood 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. www.versuchschemie.de Das aktivste deutsche Chemieforum! not_important International Hazard Posts: 3873 Registered: 21-7-2006 Member Is Offline Mood: No Mood 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 bibliomaster Posts: 2419 Registered: 7-5-2004 Location: Cornworld, Central USA Member Is Offline Mood: Enhanced  Quote: 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 International Hazard Posts: 847 Registered: 18-8-2005 Member Is Offline Mood: No Mood OK. Here is a translation thrown=up by google- translate (http://www.google.co.in/language_tools?hl=en) “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.” gsd garage chemist chemical wizard Posts: 1803 Registered: 16-8-2004 Location: Germany Member Is Offline Mood: No Mood 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. www.versuchschemie.de Das aktivste deutsche Chemieforum! not_important International Hazard Posts: 3873 Registered: 21-7-2006 Member Is Offline Mood: No Mood 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
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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]

The single most important condition for a successful synthesis is good mixing - Nicodem
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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.
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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.

The single most important condition for a successful synthesis is good mixing - Nicodem
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 Quote: 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.

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