20 replies to this topic

[slow]

I'm looking for suggestions on acetic anhydride productions at home. Maybe a way of making a home made ketene lamp? I don't have an extensive knowledge of chemistry and this makes the most sense to me.

[guitarborist]

I'm looking for suggestions on acetic anhydride productions at home. Maybe a way of making a home made ketene lamp? I don't have an extensive knowledge of chemistry and this makes the most sense to me.

Not practical.

We use this in a paleo lab and much cheaper more practical to purchase it. Especially of producing via glacial acetic acid which is somewhat tedious to produce in a lab without some dedicated resources. (again we purchase our glacial acetic).

I don't get involved in tracking our use of it but I believe it comes under some restrictive regulations.

[slow]

i can purchase the acetic acid with relative ease but purchasing acetic anhydride , well i would rather avoid the unwanted attention from big brother. I've been told that running acetone through a ketene lamp produces acetic anhydride. so Guitar are you saying that the production is minimal and is better done with acetic acid? I've also read that it can be acheived by dehydrating acetic acid at a molecular level by means of heating to a temp of 800 c. If this is correct it would be much easier for me to do. I could do so in an annealing oven to reduce the fire hazard. My question with this method besides the obvious ":does it work?" is what to rehydrate with. Everything Ive read refers to it as a liquid and H2O would put me back at the beginning again and it reacts in alcohol as well.

[Horza2002]

There is a reason why Big Brother watches those who want acetic anhydride...?

Edited by Horza2002, 22 February 2011 - 11:01 PM.

[slow]

Yes there are many reasons for monitoring AA and i have no intention of playing around with any pretty red flowers that stand on a very thin leg. However I am very fond of certain other herbs and the legalization of medical uses for them. That being said i have no need for copious sums of AA simply enough to satisfy my curiosity of forming acetates out of certain c****binoids. I hope this answers your question and you'll help me understand this process a little better.

[Horza2002]

If you were to heat it acetic acid to 800 degrees, you'd have to do it in a sealed enviroment otherwise your acetic anhydride produces would simply evapurate off (it boils at around 140oc)...although that could be way to purifity it...distill it off as any water will come off first...either that or add as dessicant to your glacial acetic acid as you heat it up.

The problem is your trying to make something that is less stable than its starting material so is is very difficult to do wiithout specialiast equipment. If you just want to form some acetates, just using acetic acid itself works...thats how I do it in the lab.

[slow]

i mistakenly used the term acetate where acetyl should have been. would this result from using GAA as well, it was my understanding that i need AA .Thanx for the info on AA but im afraid i dont quite understand.what would be added as a dessicant while heating to 800 c? how would you suggest heating it in a sealed invirament? and would using a ketene lamp be easier? I'm a experienced borosilicate glass blower and can fabricate almost any glass equipment that would be needed. I'm "slow" at initially grasping things and usally need them spelled out, hence the name. Thanx again

Edited by slow, 22 February 2011 - 08:28 PM.

[John Cuthber]

Slow,
do you understand that ketene isn't nice stuff to work with?

[slow]

i'm aware of that, but at least i understand the process and feel comfortable with it. i'm not stupid just "slow" , i have a hard time with picturing something I've never seen before.

[Horza2002]

Techincally acetate is a special type of acetyl. Ive attacked a file that shows the difference between the two for you. Basically, acetyl refers to CH₃CO group whereas acetate is CH₃C(O)O as well. Do you know specifically which functional groups you want to acetlyate? That would let me be able to tell you if acetic acid itself would be good enough.

A dessicant is a molecule that absorbs water into its structure...in the lab, we normally use calcium dichloride (CaCl₂) or heated copper sulphate (CuSO₄). You need to heat the copper sulphate because it often has several water molecules asscoiated with it and can prevent it from taking any further water from your sample. I've just had a quick look, copper sulphate melts at 200oC so won't be much use...however anhydrous calcium chloride melts at 770oC so that might work.

Mhmm...in the lab, we have specialised glass tubes (about 8mm think all the way round and not sure wht type of glass) that can have a lid screwed down when we heat samples under pressure. One of these could be used...i guess you'll know more than me if borosilicate glass would survive being heated to that temperature and under a high pressure.

I must stress, but I'm sure you already know, but having anything that high temperature will be very dangerous, especially an acid. So take care...especially your eyes.

And theres nothign wrong with needing things explained slowly...took me a long time to learn the knowledge that I have now and Im sure I would need things explained to me slowly in your area of expertise.

Attached Files

•  Doc1.pdf   49.41K   315 downloads

Edited by Horza2002, 22 February 2011 - 10:27 PM.

[slow]

horza,
thank you for taking the time to assist me and explain this in greater detail i really appreciate the help. I'll get the detail of wich groups im trying to acetyllate to you as soon as possible , some time tomorrow most likely.
As for the glass I'm guessing you use Durex rather than Pirex in applications involving that much pressure. I can order durex though through my distributor, once the GAA has reached 800 c does it need to remain at that temp for a specific amount of time ? Or is the process complete once the temp. is achieved evenly throughout the solution?
Thank you again for the info and for the link!!!

[Horza2002]

Not to worry, once you've found out it'l be much easier to try and suggest something that might work before trying to use acetic anhydride. In the lab, when trying to acetlyate something, we either use acetyl chloride (which is even more reactive than acetic anhydride) or acetic acid with a coupling agent (like DCC, EDCI); see links below. But again that depends on what your trying to do.

Im not sure this is going to work at all....its just an idea that might work; at that high a temperature everything will be a gas and I have no experience with gaseous reactions. You said that you'd found somewhere else that heating to that high a temperature could work and then I suggested adding a dessicant to make sure that any water that is relased or contaminated won't destroy your product again. Seeing as this reaction will be energetically unfavourable, it might take a while even at such a high temperature and being a gaseous reactiong will also slow it down.

Acetly chloride: http://en.wikipedia....Acetyl_chloride

EDCI: http://en.wikipedia....thylaminopropyl)carbodiimide

DCC: http://en.wikipedia....xylcarbodiimide

[slow]

ok , its taken some time for me to get back to this. i attached a file for you horza so hopefully you can let me know what you think. that is if AA in necessary.

I came across another post in a different forum that stated .


"55% of vinyl acetate is catalytically hydrolyzed to equal amounts of acetaldehyde and acetic anhydride under mild conditions and rapidly. The experimental conditions employed 2% molar ratio of PdCl2 (0.005 mol) for vinyl acetate (0.1 mol) in 60 ml glacial acetic acid stirred 1 hr at 40-80 C. producing 0.048 mol acetaldehyde and 0.05 mol acetic anhydride. "

i was wandering if you could verify this, it seems much safer and all that would be left to do after the reaction would be to filter out the PdCl2 then distill off the vinyl acetate and the acetic acid. What do you think?

Edited by slow, 26 February 2011 - 12:32 AM.

[John Cuthber]

I'm guessing you use Durex rather than Pirex

http://en.wikipedia.org/wiki/Durex


WTF?!!

[Horza2002]

To acetylate that hydroxyl group, you could treat it with potassium carbonate and acetic anhydride reasonably easily yes.

As for those other reaction conditions you found, I'm not enitrely sure about that. While I can come up with a mechanism for this transformation to give ethanal and acetic anhydride, im not sure what the palladium chloride is doing there. See my file attached for my proposed mechanism. Basically, you are doing an ester hydrolysis but in the absence of water. Once you've pronotated the vinyl acetate, water would normally attack (red arrows)...however as there is none in your reaction, the less nucleophilic acetate anion could act react instead (black arrows). The tetrahedral intermediate would then collapse to give acetic anhydride and the enol tautomer of ethanal. Seeing as ethanal boils at 20^oC, doing this reaction at 30^oC should help drive the reaction forward. I have missed out the second hydrogen transfer step in the mechanism as well to save time.

Like I said, I'm not sure why the palladium chloride is there. I know that palladium chloride is used in the synthesis of vinyl acetate as the catalyst to react ethene with acetate. So if anything, the palladium acetate will actually catalyse the decomposition of vinyl acetate back to its starting materials. There will be other ligands coordinated to the palladium during this process but I have left them off for clarity. The final step is a beta-hydride elimination, a very useful and interesting reaction...id recommend reading about its use in modern catalysis if your interested chemistry.

Attached Files

•  acet.pdf   99.21K   191 downloads

[slow]

horza,
cool , thanx for the insight. I attached the the paper on" Palladium Chloride Catalyzed Decomposition of Vinyl Acetate in Acetic Acid" in full. I'm interested to see if this answers your question on PdCl2 roll in the reaction.

Attached Files

•  Palladium chloride catalyzed decomposition of vinyl acetate in acetic acid 1-1.pdf   228.2K   173 downloads

Edited by slow, 26 February 2011 - 03:52 AM.

[mississippichem]

I wonder if the Monsanto Process might be altered to produce acetic anhydride rather than acetic acid.

[Horza2002]

Slow, the mechanism they give in that paper is the same as the on I proposed in the file I attatched (black arrows). The only differrence is that I didn't have the palladium coordinating to the alkene, which makes perfect sence actually. So I would say that might be a good way of making acetic anhydride. The key will be doing it with no water present. And like I said, if you warm the reaction up to 30-40^oC, you will boil off the ethanal byproduct and help drive the reaction to completion.

At this point I should point out that ethanal is rather a nasty compound to ingest. It has been shown that it binds irreversibly to several essential protiens that often lead to organ damage and is also a carcinogen.

Mississippichem, if you were to replace one of the iodide ligands on the rhdoium, then you might be able to eliminate acetic anhydride instead of the acid iodide. However, if you did that, then the cent.ral catalytic scheme would then stop so you would need a stoichiometric amount of methyl iodide in the reaction (warning methyl iodide is a carcinogenic).

If you were to use a different start material, methyl acetate and lithium ioidide, I wonder if this might work (see attached file). Halides are known to very mild methyl ester hydrolsis agents..although typically you use chloride in this reaction I've done this many times (by accident and on purpose). This would then give lithium acetate and mehtyl iodide that in the prescene of the rhodium catalyst would then undergo the Monstanto process to generate acetyl iodide. This would be EXTREMELY reactive and so then react with the lithium acetate to regernate the lithium iodide and acetic anhydride. So I guess the changes would be that you don't add water or methanol and then change your starting material; what you think Mississippichem?

However, if slow wants to actually do these reactions, then I think the palladium chlroide one is going to me more practial. From the experimental procedure I read in that paper, you simply add them all together and then stirr them..and if you Dean-Stark the ethanal off as it forms you should drive the reaction forward. Slow, you could make yourself a Dean-Srark apparatus to help in that reaction. Getting hold of the thr rhodium catalyst for this Montstanto-analagoude mechanism would, I imagine, prove very difficult.

http://en.wikipedia....Stark_apparatus

Attached Files

•  new.pdf   59.78K   134 downloads

[mississippichem]

Mississippichem, if you were to replace one of the iodide ligands on the rhdoium, then you might be able to eliminate acetic anhydride instead of the acid iodide. However, if you did that, then the cent.ral catalytic scheme would then stop so you would need a stoichiometric amount of methyl iodide in the reaction (warning methyl iodide is a carcinogenic).

If you were to use a different start material, methyl acetate and lithium ioidide, I wonder if this might work (see attached file). Halides are known to very mild methyl ester hydrolsis agents..although typically you use chloride in this reaction I've done this many times (by accident and on purpose). This would then give lithium acetate and mehtyl iodide that in the prescene of the rhodium catalyst would then undergo the Monstanto process to generate acetyl iodide. This would be EXTREMELY reactive and so then react with the lithium acetate to regernate the lithium iodide and acetic anhydride. So I guess the changes would be that you don't add water or methanol and then change your starting material; what you think Mississippichem?

However, if slow wants to actually do these reactions, then I think the palladium chlroide one is going to me more practial. From the experimental procedure I read in that paper, you simply add them all together and then stirr them..and if you Dean-Stark the ethanal off as it forms you should drive the reaction forward. Slow, you could make yourself a Dean-Srark apparatus to help in that reaction. Getting hold of the thr rhodium catalyst for this Montstanto-analagoude mechanism would, I imagine, prove very difficult.

http://en.wikipedia....Stark_apparatus

Oh, sorry! Didn't realize someone was trying to conduct this reaction at home! I should have read the thread more thoroughly. I would certainly never endorse the use of methyl iodide in the home [please irreversibly alkyate my DNA! ], and this would make the Monsanto process a terrible idea for the "garage chemist"; not even to mention the cost and instablility of the Rh(I) catalyst. I thought we were just speaking theoretically here. Sorry again.

However, in the name of futile speculation. I imagine that acetic anhydride could be produced industrially via the Monsanto process in the manner that you mentioned [which might I add is quite creative], or some of the acetic acid produced normally could be distilled off, reacted with thionyl chloride to give the acyl chloride and recombined with the outflow of acetic acid to give the anhydride in almost quantitative yield. Especially if the temperature was set to where the produced acetic anhydride was leaving the liquid phase as it was formed, driving the equilibrium in the spirit of the Dean-Stark trap.

I would like to hear a chemical engineer's comments on this though...insane alien, care to weigh in?

[Horza2002]

Lol yer...I was a little concerned for a minute when you suggested using large amounts of methyl iodidie in a garage...there are sooo many problems that could arise! In terms of the methods we've discussed so far, the palladium chloride is probably the best for a grage chemist (although palladium us still reasonably toxic) but is relatively stable too. I'm not sure if the route I proposed is used or not, but I just thought it might be a new method to do it...it keeps the catalytic cycle going simply by changing the conditions...and thanks, I thought it was quiet creative

The best way I would have said is to remove some some acetic acid, react it with oxalyl chloride with catalytic DMF or thionyl chloride to give the acid chrloide. That would be the best way I think industrially.

Edited by Horza2002, 26 February 2011 - 04:43 PM.