Sciencemadness Discussion Board

keten lamp

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matei - 17-3-2007 at 12:17

You can find all the information you want in Vogel's Textbook of Practical Organic Chemistry 5th Ed.

Sauron - 17-3-2007 at 13:04

If you do your own scientific glassblowing or have access to a glassblower then this is pretty easy. The hard part is figuring out how to clean the wire once if gets covered in carbon.

Also you had better have a fume hood. Ketene is very irritating, and is a known human carcinogen.

Also there are better sources of information than Vogel. Org.Syn. has better instructions for the building of a ketent lamp as well as alternate ketene generating processes. Ace Glass used to sell such a lamp and still has a two page instruction sheet for it. Organic Reactions vol 3 has a chapter on the ketene process and lamp construction details.

If you are only interested in ketene for making Ac2O there are other methods of making the anhydride that do not risk exposure to ketene. But in some parts of the world the required reagents are hard to obtain.

Nicodem - 18-3-2007 at 02:05

A link to Vogel's page? Is this some kind of a joke?

Sauron - 18-3-2007 at 10:19

Do you have a proper fume hood and other protective gear?

Because without those, making ketene is foolhardy and I for one do not wish to help you hurt or kill yourself or others.

This is not a game for the inept.

Start by learning what we mean by VOGEL.

VOGEL is free and it is on this website. I gave you a bunch of other sources, most of them also free, some of them on this website and others elsewhere on the Internet.

Sauron - 18-3-2007 at 14:17

Ketene is a known human carcinogen. Not a suspected one, not a "rasonably anticipatred to be", but one of the few KNOWN human ones. It is also extremely toxic and irritating and is comparable to phosgene in this regard. Merely doing this in open area is not enough.

What is your problem with the acetyl chloride + acetate method?

A ketene lamp at best generates about 0.4 mol ketene (and therefore, Ac2O if you bubble it into AcOH) per hour. You will need to make two or three of the filament assemblies so you can swap one out while you clean the carbon off the other a couple of times per day. I have yet to work out a really efficient way to do that. The literature talks about scraping the carbon off the nichrome wire, which strikes me as laborious and fiddly, likely to result in broken filament.

There are also tube-furnace type ketent generators but these usually run about half as fast as the ketene lamp (if you want to call that fast.)

My advice is: work out your problem with the other method.

Forget about ketene for the sake of your health. Maybe your life.

Sauron - 19-3-2007 at 10:21

A bench scale ketene lamp will make at best 0.45 mol per hour.

A mol is the molecular weight in grams. Ac2O is MW 102 so the lamp will produce about 46 g per hour.

Those wattages are way to high.

Sauron - 19-3-2007 at 16:22

I will prepare a zip file of all the ketene generation material I have. And I will post it here.

The wire is usually a specific nichrome or monel alloy, specified, or else platinum, the latter being obviously expensive.

The wire is a common resistance type for heating elements, and the electricity needed is just enough to heat it to c.700 C. or less as specified in articles.

You will need a competent scientific glassblower to fabricate this. No one makes these commercially any more although they used to. You might be able to induce someone to make one for you custom.

I assembled this file as a pdf in case you don't have a archive file applet.

It contains

Chapter 3, Org.Reactions III
Vogel pp 372-374
Ace Glass instruction sheet for Ketene/Butadiene Lamp
A US patent
Two Org.Syn. articles
A journal article

You know have as much information as I do. Use it wisely, use it well, and don't hurt yourself or anyone else.

Download the file ketene.pdf here:

http://www.4shared.com/dir/2245331/5a78115f/sharing.html

[Edited on 20-3-2007 by Sauron]

[Edited on 20-3-2007 by Sauron]

lamp.jpg - 52kB

Sauron - 20-3-2007 at 02:08

1. For a tube furnace, tube can be Pyrex.

2. The nichrome does not participate in reaction. It's the heaet that does the work. One article recommends Platinum wire not nichrome.

3. The composition and diameter of the wire are important electrically, it is a resistance element.

Redistill your acetic anhydride using a fractionating column and take off product with correct b.p. only.

Sauron - 21-3-2007 at 00:04

Balloon? A balloon has nothing to do with it.

I do not have any information about scaleup of ketene process to pilot plant scale. The various bench scale processes we have detailed for you will at lest produce 500-1000 ml a day based on 24 hrs operation. I frankly do not think running this around the clock is advisable, and you are talking about a scale 20-40X larger than that. That is the realm of chemical engineering my friend, and what do you need 20 L a day of Ac2O for anyway/ That does not sound like amateur science to me.

Perhaps it is fortunate that you do not appear in any danger of success.

leu - 21-3-2007 at 05:50

A balloon flask is an alternative name for a round bottom flask, see this URL which has been mentioned repeatedly and look for balloon flask:

http://www.labxnews.com/labxnews279.htm

:P

Sauron - 21-3-2007 at 07:44

He just said balloon nothing about flask. Had he said balloon flask I would have understood that to mean RB flask.

However my remarks still stand. Anyway flask size is not very germain, the limiting factor is the boilup rate of acetone that the system can handle. Exceed that and all one gets is mostly unaltered acetone in the receiver.

Sauron - 21-3-2007 at 18:46

All right, @hector, sorry if I was a little cross. Are you acetylating wood upulp, or cotton?

I see there are processes for cotton using AcOH + H2SO4; and wood pulp using Acetic acid/Ac2O mixtures with H2SO4 catalyst. I wonder why acetyl chloride can't be used? As you obviously can and must obtain it to make your Ac2O, and just as obviously either can't obtain the anhydride or else it costs too much. And so you are attracted to the ketene process, despite its high risks.

The only document I gave you that describes anything scalable to 20 L/day is that US patent. The Org.Reactions Vol III article contains a lot of references some of which might be to industrial processes. It seems to me that the tube-furnace process might be more easily scaled up than the ketene-lamp. This despite somewhat lower efficiency on bench scale.

See if you can buy where you are, DIKETENE (ketene dimer) because that can be efficiently cracked back to ketene more efficiently than acetone etc. can be pyrolyzed. However I don't know if this will be economical for you.

Can you replace your metal beakers with plastic ones or line the metal ones with teflon or glass to stop the reaction with acetyl chloride? Or you might try decolorizing the anhydride with Norit (activated carbon powder) then filtration.

I will be happy to help (and I'm sure the other members will too) if we can solve your problems for you. The more we know about your process the more chance we have to be of practical assustance. We don't get to advise commercial operations very much.

DMAP is 4-Dimethylaminopyridine. It is available in prilled form which is easier to handle (and safer) than other forms. Maybe DMAP will allow you to eliminate Ac2O from your process, and use AcOH/H2SO4 instead. I don't know, it is only an idea.

------------------

I just read up on celluose acetate in Ullmann's. It seems that all of the bright ideas I listed above have been tried without success, including direct acetylation of cellulose with ketene which I thought of but didn't suggest. Here attached is most of the Ullmann entry on this subject with references (attached as text)

Of particular interest is the Wacker Chemical process for acetic anhydride from ketene and AcOH which is mentioned under recovery of acetic anhydride. I will go look into this now.





[Edited on 22-3-2007 by Sauron]

Attachment: celluloseacetate.txt (32kB)
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not_important - 21-3-2007 at 23:58

It sounds as if your use falls into the hole between what is practicable on lab scale and on industrial scale. This usually is the range where you buy reagents, rather than making them yourself, or buying the end product; the large manufactures can turn stuff out so much more cheaply than you can on a small scale that it's just not economic to try to.

Industrially acetic anhydride is made via a ketene process, cracking acetic acid rather than acetone. Some is made by carbonylation of methyl acetate. Much of the acetic anhydride produce is captive, being used ((often on-site) to make cellulose acetate. This usually uses a mixture of acetic acid and anhydride with sulfuric acid catalyst.

The hot tube routes are the way to go for large scale, but as already been emphasised you are dealing with a rather toxic substance, phrases such as Yokkaichi Asthma and Bhopal come to mind. The life you save is likely your own.

A monograph on acetic anhydride.
http://www.inchem.org/documents/sids/sids/108247.pdf

This may be of interest to you

Attachment: Process Flowsheeting Calculations for Acetic Anhydride Plant.pdf (73kB)
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Sauron - 22-3-2007 at 03:11

According to Ullmann's Encyclopedia of Chem.Technology (2003):


"Two other methods also were used in the past: the cleavage of ethylidene diacetate to form acetaldehyde and acetic anhydride in the presence of [NB Sauron: Lewis] acid catalysts, such as zinc chloride, and the reaction of vinyl acetate with acetic acid on palladium(II) contacts to form acetaldehyde and acetic anhydride [16]. Not one of these processes is now of any industrial importance."

If you can buy vinyl acetate or ethylidene diacetate -- both are acetylenic derivatives -- then these may be worth looking into. Vinyl acetate CH2=CH-OAc Ethylidene diacetate H2C=C(OAc)2

I just looked up prices. Vinyl acetate is cheap and sold in volume (2.5L from Acros $33 US) Ethylidene diacetate is horribly expensive from same source 100 g >$100 US. So I would focus on vinyl acetate. Warning: flash point -8 C.

Let me look at reference 16 and see what this process looks like but this one just might be of use to you.

Well ref 16 is Ullmann's 3rd ed, Vol 6, p.804. Which I do not have. Can ahnyone help?

[------------

I am on the trail of this now. Acetylation of sec. alcohols with vinyl acetate over PdCl2/CuCl2 is a known reaction with acetaldehyde as byproduct so it seems like in absence of an alcohol to acetylate, the actual acetylating agent (Ac2O ?) will be isolable. Therefore the system PdCl2/CuCl2 seems to be the catalyst. I am ferreting out details. This could be a winner, easily scaled to the 20 L/day Ac2O that is desired, and with fillip of acetaldehyde byproduct readily oxidized to AcOH which @hector2000 can utilize as well.

Got it! Clement and Selwitz, Tet.Lett.1962, 1081. PdCl2 catalyzes conversion of vinyl acetate into acetaldehyde and acetic anhydride in glacial acetic acid containing sodium acetate. .

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 think we have a ball game here.

[Edited on 23-3-2007 by Sauron]

Attachment: Palladium chloride catalyzed decomposition of vinyl acetate in acetic acid [1].pdf (228kB)
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not_important - 23-3-2007 at 01:10

The palladium is recoverable and reusable. You want to use acetylene, if you're doing that route to the anhydride. Ketene reacts directly with water to give acetic acid and with acetic acid to give acetic anhydride, you don't need any other reagents.

I'm pretty sure ketene and HCl give acetyl chloride, but why? If you want it to react with sodium acetate, ketene plus acetic acid gives the anhydride in fewer steps with higher yield and easier workup.

Again, one industrial process is effectively ketene + acetic acid => anhydride, the ketene being form in the gases by dehydration over an AlPO4 catalyst.

The references I've seen for making cellulose acetate all use a mixture of acetic acid and acetic anhydride, with a bit of sulfuric acid. There doesn't seem to be a great need to isolate the anhydride. The cellulose can even be acetylated by suspended the cellulose in acetic acid and passing in ketene.

Why not just buy the anhydride, or even the cellulose acetate? The manufactures of it have spend decades optimizing their acetic anhydride production, and do it on a huge scale. There's no way you can make acetic anhydride as cheaply, efficiently, and as pure as they can. Likewise they've got their reagent recovery down to a 'T', they waste as little of the raw materials as possible so their cellulose acetate is likely to be cheaper than you can make it.

Sauron - 23-3-2007 at 01:29

After the reaction, you will have a mixture of acetaldehyde, acetic anhydride, unreacted vinyl acetate (to recover and recycle), acetic acid (recover and recycle) sodium acetate (recover and recycle) and PdCl2 catalyst (recover and recycle)

The PdCl2 is a heterogenous catalyst, it is insoluble in that mixture so first thing you do is filter the mixture to remove the PdCl2 (or perhaps it is Pd metal by then, I am not sure.) In any case you should be able to recover it quantitatively. That means you only have to buy it once. If it remains as PdCl2 then you just wash it and reuse it. If it has become Pd metal you must digest it in HCl and recover it as PdCl2.

So now you have AcOH, Ac2O, acetaldehyde and vinyl acetate and some sodium acetate. The acetaldehyde is quite low boiling (21 C) and will distill off first. My advice would be to oxidize it to acetic acid which you can use anyway as you have no use for the aldehyde that I know of.

For the rest let's look at boiling points.

Vinyl acetate 72-73 C
Acetic anhydride 140 C
Acetic acid (glacial) 117-118 C

So the unreacted vinyl acetate will come over second, now all you have left is AcOH and Ac2) and sodium acetate.

Now you don't want to have to distill off all that acetic acid and you would rather remove the anhydride instead. Sounds like a job for liquid-liquid extraction. Let's look for a solvent that will extract the relatively small amount of anhydride from the larger amount of acid without dissolving the acid. If you can do this you don't need to distill the acetic acid at all, or seperate the sodium acetate, you can just use them in the next run.

@n_i, we are onto a completely different process here. The ketene process is too dangerous and in fact is obsolescent since the mid 70s because of the high energy costs (truer now than then!) but lingers on because of the high cap.investment in those plants. The Halcon process and catalytic oxidation of acetaldehyde through peracetic acid is not downsizable. So we are looking at catalytic hydrolysis of vinyl acetate w/PdCl2 in AcOH instead. This liquid phase, at atmospheric pressure, decent yield and so we are looking at the workup.

If you go look at the acetic anhydride thread I found another prep, dry reaction of sodium acetate with N2O4 gives Ac2O and NaNO2 and N2O3 (Balanced eq is there not here.) However I don't think our friend @hector2000 wants to get up close and personal with enough N2O4 to make 20 L a day anhydride, he might as well be breathing ketene or phosgene. Also I have few details on this 1930s Russian process.

[Edited on 23-3-2007 by Sauron]

Sauron - 23-3-2007 at 02:48

Acetaldehyde is far far LESS irritating than acetic anhydride and even less than ketene which is deadly. Ketene if it doesn't kill you now will kill you later (carcinogen) and there just isn't any getting away from this simple fact. So unless your factory is in the middle of nowhere this will be a danger not only to you and your staff but also your neighbors (remember Bhopal? Ketene is a lot worse than methyl isocyanate.)

Vinyl acetate is higher boiling than acetaldehyde but has a much lower flash point. For that matter acetic anhydride is also very flammable.

Since the vinyl acetate hydrolysis is run at 40-80 C and acetaldehyde boils at 21 C obviously you can cimply take off and condense acetaldehyde as it is formed which will be easier than refluxing it which would require recirculating chillers at <0 C or maybe Dewar condensers with freezing mixtures.

Maybe you can reduce the amount of acetic acid solvent and you can determine this by smaller scale trial and error.

I think you will find that you can achieve certain economies with the PdCl2 because you can reuse it from batch to batch with essentially no losses. Let me make some calculations. I will work backwards from 20 L a day anhydride and see what batch sizes, reactor sizes and number of batches/day pop out.

----

Meanwhile you have a working process (AcCl + Na acetate) but it is giving you problems, let's look at your problems. Supplier of acetyl chloride is an idiot using improper container and contaminating reagent with FeCl2, correct? Is changing to another supplier an option? Or can you convince present supplier to package the acetyl chloride properly so to eliminate the iron salt problem?

Can you purchase cyanuric chloride? This is cheap. Reflux 1 part of CC with large excess of AcOH and you get 3 parts acetyl chloride in there which you can strip off the acetic acid easily as it boils low. (By product cyanuric acid ppts out, filer it off, resuse acetic acid with more CC.) This way you make your own acetyl chloride and reduce costs while eliminating FeCl2 problem.

A little more expensive, you can buy oxalyl chloride and make acetic anhydride from acetic acid directly with it.

Or you can make the oxalyl chloride from oxalic acid and CC then use the oxalyl chloride to make acetic anhydride. In these last two methods you bypass acetyl chloride completely.

You haven't told us why you can't just buy acetic anhydride, but I assume you can't. In this country I can't buy either anhydride or acetyl chloride so I must make my own but I don't need 20 L a day! Maybe 5 L a year.

Sauron - 23-3-2007 at 04:23

Of course acetic anhydride is highly restricted here for same stupid reason. But I am sure they make cellulose acetate here and so they get a license to import from the Defense Ministry who control this. Acetyl chloride also. And many other things.

CC is solid, it smells but it is not dangerous to handle it, I have many Kg in my home. In EU they consider it toxic but they consider lots of things toxic because of the Green politics. There's a difference between pretend toxic and TOXIC. Ketene is REALLY TOXIC. So my advice is to stear clear of that process.

We will find you a way to get this done that won't kill you and won't bankrupt you.

I understand your problem.

The acetyl chloride, is it already contaminated before you open the bottles or does it only become contaminated (yellow) later?

Have you tried decolorizing it with powdered activated carbon like Norit? Just put in a few grams per liter, stir, filter, color should go away (trapped in the carbon). You would want to do this in closed flasks otherwise the acetyl chloride will fume badly and stink up the place. It is more irritating than acetaldehyde.

If we solve this problem with acetyl chloride then you will at least have a good process till you can find a better/cheaper methed with or without our help.

Another member has suggested a US patent that says you can make Ac2) from vinyl acetate without PdCl2, I am investigating.

And I am still looking into how to get the Ac2O out of the acetic acid without distillation.

The other name for CC is TCT and it is used to make agrticultural chemicals, it is cheap. In fact I have seen articles about it by chemists at universities in Iran so it ought to be available in your country maybe manufactured there. I will get the full name for you and the CAS number. The name is trichloro-s-triazine, or cyanuric chloride.

Eclectic - 23-3-2007 at 05:04

You can't use cellulose acetate molding powder from the plastics industry?

:o

Sauron - 23-3-2007 at 05:29

@hector 2000 already explained that in his country cellulose acetate is $30/Kg, and he is making his own to save cost. If he cannot solve problem of better way to make his own Ac2O he will have to close his company. He needs to make 20 L a day anhydride to produce 50 Kg/day cellulose acetate. He is presently making Ac2O from acetyl chloride and sodium acetate but the acetyl chloride he can buy (locally made apparently) is packeged badly and contaminated with FeCl2 so is yellow. The good news is, it is cheap.

@hector, are you fusing the sodium acetate prior to reaction? It needs to be totally anhydrous, so you need to melt it in a drying oven at 125 C then break it up and powder it, all this just before using it, or you will get less acetic anhydride because part of the acetyl chloride will be used up reacting with the water of crystallization. This also true of sodium acetate in the vinyl acetate method.

Sauron - 23-3-2007 at 06:33

I suspect your supplier is making acetyl chloride by POCl3 or PCl3 and not purifying so still contains some phosphorus compounds. Or could be sulfur compounds from SOCl2. If I were you I would distill the acetyl chloride before using and bottle it in amber (brown) glass bottles only with corrosion resistant caps and store it away from light in a cool place. Obviously the acetyl chloride is passing the P or S contamination along to the acetic anhydride and this is source of your problems.

CC (TCT) is CAS registry number 108-77-0. Name 2,4,6-trichloro-s-triazine. If you make acetyl chloride from this it will never turn yellow or red. But store it properly cool and dark in brown glass and don't use a cap it will attack.

not_important - 23-3-2007 at 09:03

Quote:
Originally posted by Sauron..,

@n_i, we are onto a completely different process here. The ketene process is too dangerous and in fact is obsolescent since the mid 70s because of the high energy costs (truer now than then!) but lingers on because of the high cap.investment in those plants. The Halcon process and catalytic oxidation of acetaldehyde through peracetic acid is not downsizable. So we are looking at catalytic hydrolysis of vinyl acetate w/PdCl2 in AcOH instead. This liquid phase, at atmospheric pressure, decent yield and so we are looking at the workup.
...
[Edited on 23-3-2007 by Sauron]


At the time I replied you'd moved on, but
Quote:
Originally posted by hector2000
what is carbonylation of methyl acetate method?
is method better than keten method?
and may i replace the acetylen gas with keten?
and another question:
HCL+KETEN->ACETYLE CHLORIDE
this reaction may be true?
[Edited on 22-3-2007 by hector2000]


which meant he was still thinking about ketene for one reason or another.

The vinyl acetate method is related to the older acetylene + acetic acid => ethylidene diacetate => acetic acid & acetaldehyde. As vinyl acetate can be (& was) made by adding acetic acid to acetylene, all that process you found does is effect put an extra step in. This could be handy as you point out vinyl acetate is a commodity and easier to fling about than acetylene; on the other hand vinyl acetate will contain polymerisation inhibitors that might cause problems (distill the VA into the reaction mix?).

The point here is that process goes back to somewhere in the 1920s, it's mentioned in J.B. Conant's Chemistry of Organic Compounds, a textbook published in 1934. Finding some industrial references from that period could help with the workup. Same book has anhydride being made with S2Cl2 and sodium acetate. Alas, no references for either method, it's just a textbook.

BTW - ethylidene diacetate can be split into vinyl acetate and acetic acid, and it can be made from acetaldehyde and acetic anhydride; the reverse of the reaction you've been researching, and used in the US around mid-century.

Could hector transfer the acetyl chloride into all glass temporary storage immediately upon opening the container? If the color problem is iron introduced by corrosion this might help.

Sauron - 23-3-2007 at 10:51

@n_i, if you look carefully I mentioned ethylidene diacetate -> acetaldehyde + acetic anhydride but I also checked the price and ethylidene diacetate is about 100 times more expensive than vinyl acetate so I dropped it like a hot rock. Vinyl acetate is cheap. Acros sells 2.5 L for $30. Largest vottle of ethylidene diacetate is 100 g # $122. Furthermore, although anyone who has googled the subject would know that in essence this is a reversible reaction, and acetaldehyde + acetic anhydride is catalyzed by Pd(II) to vinyl acetate, if you read the article from JOC by the two chaps from Gulf (the Seven Sisters) you will see that the particular reaction conditions at hand do not proceed through ethylidene diacetate and that in fact that substance is entirely unreactive under those conditions. Therefore ethylidene diacetate merely muddies the water.

Thanks for your suggestion regarding rebottling the acetyl chloride but, again, read what I already posted and you will see I did think of that and already suggested it as a remedy. According to @hector2000's latest, the acetyl chloride is Merck product. This is really odd, Merck ought to know better than to package something in such a fashion, wouldn't you think? Also while yellow sounds like FeCl2, red does not and this stuff goes red, and the Ac2) made from it also goes first yellow then red. This is most odd.

@hector2000, I have in the past used Russian method which is anhydrous sodium acetate plus sulfur and bromine to make acetic anhydride. Presently I have purchased CC so I can make oxalyl chloride and with that make either acetyl chloride or acetic anhydride as needed. Also I am buying oxalyl chloride as well but it is not cheap. Better to make it from cheap CC.

I have no experience with the persulfate reaction but I know that some European members are looking at it because they cannot easily buy CC. I don't have this handicap, so I have not examined this reaction carefully. For me CC is easy and cheap and versatile. I can make with it acid chlorides, acid bromides and iodides, alkyl chlorides, and particularly oxalyl chloride. With that I can make anhydrides directly. Also inorganic acid chlorides that are hard to buy here. CC is also useful for a number of other transformations.

So far I have found only one solvent that acetic acid is insoluble in, carbon disulfide. I am not yet certain whether or not it dissolves acetic anhydride. The main difference between the acid and the anhydride is that the former is protic and the latter is not. We can exploit that. I am still investigating. CS2 is a little too flammable for my liking, you will already have enough problems with vinyl acetate. I will report as soon as I have news.

Sauron - 23-3-2007 at 12:06

I am first to concede I am not a chemical engineer. On the other hand, making 20 L or 50 L a day is NOT industrial scale. On industrial scale things are usually done on a continuous basis not on batch scale (whenever possible) and generally are automated. You don't want or need any of that to make 50 L a day or 20 L a day, you are not working round the clock and you are working in batches not continuous processes. So you are working in a large bench scale.

I'm a retired guy not a student. It has been a long time since I was a student. When I was a student Reza Pahlavi was still running your country, if that puts things in perspective. However I never stopped studying...


Here's a tip. If you have to filter something unpleasant like acetyl chloride and you don't want to have to deal with the fumes from a open top Buchner funnel, you set up a pressure filtration appartatus and you use air or inert gas (as appropriate) to move the liquid through tubing to a closed fritted disk funnel. You must make sure your gas pressure does not exceed the mechanical strength of the fritted disk.

This is similar to moving air sensitive reagents from bottle to reactors.

leu - 23-3-2007 at 14:30

The separation of acetic anhydride from acetic acid is rather simple if one has the proper equipment :P

Attachment: US5264087A1.pdf (197kB)
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Sauron - 23-3-2007 at 21:08

Thanks, @leu. Unfortunately this while interesting is not helpful. @Hector has all but totally discarded (on my advice) the ketene process. The patent you attached involves vac.disitllation of 83-85% Ac2O with AcOH for rest plus traces of diketene.

The recommended prep, vinyl acetate over PdCl2 -> acetic anhydride + acetaldehyde, is conducted in AcOH as solvent. Therefore unlike the system above, in this process and after removal of acetaldehyde and unreacted vinyl acetate, which are lower boiling, the mixture is predominantly AcOH containing a relatively small amount of Ac2O. Since AcOH boils 23 deg C lower than the anhydride, distillation would be lengthy and tedious.

Therefore we are looking at liquid-liquid extraction of the Ac2O from the AcOH with a solvent that is immiscible with the acid but that will dissolve the anhydride.

@hector2000 needs to produce 20 L/day anhydride and this scale is too large for bench and way too small for an industrial process. He is presently using Merck acetyl chloride and anhydr. sodium acetate to make 50 L/day Ac2O but is having problems with the Merck acid chloride turning ywllow then red and passing that contaminant on to the anhydride.

Magpie - 23-3-2007 at 22:30

I don't think of Merck as an industrial supplier of something like acetyl chloride. I think of them more as a supplier to research and educational institutions. Am I wrong here?

If I'm correct in the above it seems like 20L/day would be a large acetyl chloride customer for Merck. On that basis Hector ought to be able to work with Merck to work out Merck's apparent quality problem for Hector. Has that been tried Hector?

It just doesn't seem right that Merck grade acetyl chloride would be of poor quality. Merck is a pharmaceutical manufacturer and maker of fine chemicals. They ought to have quality down to a gnat's ass.

Hector: What is the grade anyway? Technical? lab grade?, or what?

Sauron - 23-3-2007 at 22:50

I think you will find that Merck sells lots of chemicals in bulk just as Aldrich does, Acros does, Eastman does, Carlo Erba does, Panreac does, and so on. A cursory look at the websites or print catalogs will reveal request cards for bulk quotes and/or lists of bulk products from all of these companies. None of these companies could survive on just the research and educational markets.

Magpie - 23-3-2007 at 22:58

OK, so maybe Hector's 20L/day order is no big deal to Merck. It still seems strange that Merck would have a quality problem with their acetyl chloride, unless, of course it is due to something unique in Hector's process, and no other customers complain.

Sauron - 23-3-2007 at 23:13

@Hector's process is to add AcCl to NaOAc anhydr. Perhaps the (stainless?) steel vessels are being attacked by the acid chloride. That's what he thinks. I am not so sure. FeCl2 is not red. He is getting first yellow then red.

UnintentionalChaos - 23-3-2007 at 23:27

That sounds right. Note the discussion on this page relating to color. http://jchemed.chem.wisc.edu/jcesoft/cca/CCA3/MAIN/CLFE/PAGE...
There is probably water in the reaction vessel somewhere, although that isn't the only problem since the steel vessels are not inert.

Sauron - 24-3-2007 at 00:22

@Hector, please take note. Try avoiding any contact between the acetyl chloride and the acetic anhydride with iron, steel or stainless steel. The red color may be FeCl3, the yellow color FeCl2.

When you open fresh bottles acetyl chloride transfer the liquid out of the bottle without pouring it over the metal part. Use a siphon system of something intert like glass or PTFE. Store the acetyl chloride like I told you in brown glass with inert plastic caps away from light and heat. Do not use metal vessels for reaction with NaOAc. Do not stir with metal. If you do this you should not have color problem, anhydride should be water white.

Sauron - 24-3-2007 at 01:52

You are buying reagent grade acetyl chloride from Merck in a 200 L drun. This is PE lined steel. I think we all assumed you were buying many many 1 L or 2.5 L bottles. How silly of us! Anyhow the "for synthesis" grade of Merck is as good as it gets.

Magpie - 24-3-2007 at 09:27

I think that is a very good experiment you are trying, ie, conducting the process on a lab scale using no metal vessels or equipment. That should help in isolating the cause of the discoloration.

In fact, why not do it on a small scale with just glassware. See if the color remains or disappears.

not_important - 24-3-2007 at 10:09

The CO2 + acetate routes, one gives Na2CO3 and the other NaHCO3, basically treat a solution or suspension of sodium acetate with high pressure CO2 at slightly elevated temperatures 30 - 60 C, then cooling to 0 C or below, letting it sit for awhile, and separating the carbonate/bicarbonate from the liquid containing acetic acid and acetic anhydride. At that point the anhydride must quickly be separated from the aqueous materials, solvent extraction being the best.

It works, I've tried it, but it does not seem to have made it commercially. I suspect loses of anhydride were too high for the quality of the product. A version using up-to-date methods might be practical, but you'de be doing full blown R&D.

leu - 24-3-2007 at 12:22

This patent mentions the use of toluene :P

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leu - 24-3-2007 at 12:25

Toluene is also within the specified class of aromatic hydrocarbons mentioned in this patent :P

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Sauron - 24-3-2007 at 16:42

I am very dubious of the CO2/acetate method, as the extraction of anhydride has to be done fast enough to preclude hydrolysis. So mostly it's a good way to make acetic acid, because that's what most of the Ac2O formed will turn into. You've got seconds to minutes of half life to seperate solids and extract the anhydride and dry it. The key parameter is the temperature dependent half life of Ac2O in water. To give yourself half a chance of recovering even part of the anhydride, you need to use only near-freezing water.

@hector2000, I gave you CAS number of cyanuric chloride. You want the Merck number? They sell it, and you buy from Merck in bulk. Yes it is a common chemical particularly in agro-chemical industry for making triazine pesticides.

[Edited on 25-3-2007 by Sauron]

leu - 24-3-2007 at 17:38

There are a variety of methods that have been patented for the production of acetic anhydride that have never been commercialized for one reason or another that may be most suitable for a cellulose acetate manufacturer in a restrictive country such as Iran :( The procedure that makes the most sense would be to hire a chemical engineer to evaluate the various processes in terms of the cost of what materials and equipment are available and compare that to the profits that can be gained to see if any such process is economically feasible and then decide what to do at that point :P For example, there's a little known process that uses acetic acid in a copper still that may be perfectly suited for your purposes since acetic acid can be produced by the destructive distillation of wood along with methanol, this way you could reduce your dependence on Merck :cool:

[Edited on 25-3-2007 by leu]

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Sauron - 24-3-2007 at 18:19

@leu, please don't overlook the simple fact that @hector's requirement is barely larger than large bench scale. He is talking 20 L a day. He is not looking to invest millions in a giant industrial operation. Heb has two tasks:

1. Find a suitable less costly and less problematic alt. to his present acetyl chloride-sodium acetate process. Note that lab grade AcCl Merck costs him only $6 US/Kg (or maybe L) as he buys it in 200 L drums. I am sure that we all wish we could get it for that price. In my case I can't buy it at any price.

2. He has a wee problem with contamination (we think Fe(II)/Fe(III) chlorides in present process. If we can help him eliminate this problem then he can at least stick with what he has if we can't find him a cheaper route.

He is cool to my suggestion of vinyl acetate route because of cost of PdCl2 catalyst, He would need about 4 Kg PdCl2 and that isn't cheap. However, it is a one time capital cost as it is reusable, it's heterogeous catalyst and is not consumed.

If he prepares his own PdCl2 from say 2 Kg Pd metal what is spot market price for Pd? This would be a lot cheaper than buying PdCl2 commercially. PdCl2 is c.59% Pd. The spot market price for a troy oz is about $350. So $23 a gram roughly. $46,000 for 2 Kg. So something less than $10 per L catalyst cost first year. What is catalyst life cycle? Other than mechanical losses it will not go away. If this was a hydrogenation we would talk about poisoning of catalyst but, it isn't. Is it reasonable to anticipate a catalyst life of more than a year? If so then amortized catalyst cost/L plummets rapidly. $5/L 2 years $2.50/L 4 years.

(If he makes 100 L (Ac2O) a week that is 4800 L/year (we must deduct Ramadan when he cannot work.) So he has all that product over which to amortize his catalyst cost.)

Hmmm, I guess it is easy to see why this Pd(II) process can't compete economically. Oh well. too bad, it looked good otherwise.

------------------------

Acros sells cyanuric chloride for $34/Kg for 1 Kg pack. Now @hector you can probably improve considerably on that by buying in bulk just as you do with acetyl chloride. Acros price for acetyl chloride $45/L in 2.5 L pack. So I would not be surprised if you can get CC for $5/Kg in 200 Kg pack. Get a quote from Merck and find out.

One Kg CC makes about 1.4 Kg acetyl chloride. That's about 1.25 L as the density of AcCl is 1.1

Therefore, making acetyl chloride from cyanuric chloride is competitive with your cost of the Merck product, assuming your cost for AcOH is low.

I did not calculate in the cost of energy to distill the acetyl chloride from the AcOH, but, AcCl boils at 51 C compared to 117 C for the acid, a 66 degree spread, so this is an easy seperation. A simple distillation will suffice, maybe two at most.

Merck's product number for cyanuric chloride is 802815.



[Edited on 25-3-2007 by Sauron]

Sauron - 24-3-2007 at 22:36

I believe both acetic acid and acetic anhydride are totally miscible with benzene and toluene. So you can't extract anhydride from acetic acid with those.

So far the only solvent we have found that will do this job is CS2.

Acetic acid is practically insoluble in CS2.

Acetic anhydride is miscible with CS2 in certain proportions.

There may be other solvents that will work, but we haven't identified them as yet. I would think that sulfur containing hydrocarbons like thiophene, sulfolane etc are strong candidates. Someone else suggested monochloropentanes. But unless we can find examples in the literature you will have to experiment, or someone will have to experiment, to find this out. So far the standard texts on laboratory and industrial solvents have been useless. I will keep on looking.

By the way benzene is a bad carcinogen.

Sauron - 24-3-2007 at 23:19

That Daicell patent is concerning treatment off offgases from ketene process.

Look at data sheets for AcOH and Ac2O and you will see both are miscible with benzene. That means they dissolve in all proportions. Benzene is useless for you in liquid phase seperation of AcOH and Ac2O. Do not be confused by that patent.

The CO2 acetate process involves treatment of aqueous sodium acetate solution with CO2. It appears to me that solid CO2 in snowflake form would be best, as you want the water as cold as possible to slow the hydrolysis of Ac2O formed. You have very blittle time to extract Ac2O into organic phase (chloroform is best) before the Ac2O will react with water forming AcOH. And the AcOH will react with sodium carbonate or bicarbonate formed to produce more sodium acetate so this process goes in a circle. If and only if you can efficiently extract Ac2O into a hydrophobic organic phase will this be productive of Ac2O for you. To me it sounds like a Chinese fire drill. It's like a dog chasing his own tail.

[Edited on 25-3-2007 by Sauron]

[Edited on 25-3-2007 by Sauron]

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Sauron - 25-3-2007 at 01:01

Put that question aside for the moment.

Here are two US patents from 1930s.

First one says vinyl acetate + acetic acid over conc sulfuric acid as catalyst, gives acetaldehyde and acetic anhydride. Claims 77% conversion and 95% recovery of the anhydride formed. No PdCl2 required.

Other catalysts suggested include phosphoric acid, sulfonic acids like p-toluenesulfonic acid (the example they give is benzenesulfonic acid), etc. as I know you have a problem with sulfuric acid.

This would be very cheap and easy. No acetyl chloride needed. No PdCl2 needed. You should try this. No sodium acetate needed. So no more 3 day drying oven.

Don't thank me, thank @S.C.Wack who pointed these out in another thread.

The second patent says that heating trichloroethylene (which they call methyl chloroform) and water in an autoclave (pressure reactor) to 75-150 C for 10 hours gives excellent yields of AcOH, AcCl, or Ac2O depending on ratio of trichloroethylene:water.

1 part trichloroethylene to 1 part water -> acetic acid

2 parts trichloroethylene to 3 parts water -> acetic anhydride

1 part trichloroethylene to 2 parts water -> acetyl chloride

When I say parts read mols.

Catalyst: H2SO4 (AcOH only), FeCl2 anhydrous, ZnCl2, CoCl2, etc.

Hydrochloric acid by product.

This patent was to Dow Chemical.

If you can still get 1,1,1-trichloroethylene in Iran you may want to try this

[Edited on 25-3-2007 by Sauron]

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Sauron - 25-3-2007 at 02:22

In the first reaction you start with vinyl acetate and acetic acid. Supposedly 77% of the VA reacts so that means 77% of the acetic acid does. Therefore 23% of AcOH is left. So you have a mixture of acetaldehyde (but you take that off during the reaction), VA (distill it off), a lot of Ac2) and a little acetic acid. Much easier to seperate by distillation than in the PdCl2 catalyzed process.

In the second reaction we are told that the conversions are very high percentages, so in case of acetic anhydride you will have minor amounts of trichloroethylene, water, and a lot of HCl. The HCl is gasous rather than aqueous. You offgas it from the liquid product with vacuum. Once again this purification by distillation is easy.

Am I sure of this reaction? I haven't tried it yet. But you can read the patents for yourself. Just try them. They look simple.

2 CH3-CCl3 + 2 H2O -> (CH3-C=O)2O + 6 HCl

Sauron - 25-3-2007 at 04:28

I named that a little wrong, it is 1,1,1-trichloroethane.

Industrially making Ac2O out of vinyl acetate makes little sense because vinyl acetate is made from Ac2O.

However, if this patent is geuine and reaction works, this is a good way to make Ac2O on a scale from lab bench to your 50 L/day as the VA is cheap, the catalysts are cheap (various transition metal chlorides) and the conditions are not harsh.

The acetaldehyde you condense and oxidize to AcOH

The byproduct ethylidene diacetate you add to the pot for next batcg as it behaves just like VA + AcOH

The Ac2O yield is higher than in the Gulf Research PdCl2 cat. process.

And the product is more easily worked up.

This really looks good if it works. Easy enough to find ut. We are all hoping it does because if so we can use it too. For many of us both acetaldehyde and Ac2O are highly desirable.

Good luck!

[Edited on 25-3-2007 by Sauron]

evil_lurker - 25-3-2007 at 09:28

I noticed that it was mentioned by using CC or TCT acetyl chloride could be formed... I was under the impression that this would form chloroacetic acid instead of the acetyl chloride.

Sauron - 25-3-2007 at 19:09

I think you are confusing TCT with TCCA. And then misremembering what TCCA does.

TCT (CC) chlorinates carboxylic acids to acid chlorides; and it chlorinates alcohols to alkyl chlorides. It is 2,4,6-trichloro-s-triazine. Its three chlorines are on carbon.

TCCA is trichloroisocyanuric acid. Its three chlorines are on nitrogen.

Both of them form cyanuric acid upon hydrolysis, TCCA by rearrangement.

TCCA can be regenerated with chlorine. TCT cannot.

TCCA is swimming pool chlorinator.

TCT is trimer of cyanogen chloride and is feedstock for triazine pesticides.

TCCA selectively chlorinates secondary alcohols only.

TCT chlorinates primary and secondary alcohols.

The structures of both have been posted here previously. So don't let the similar acronyms fool you.

jimmyboy - 26-3-2007 at 00:17

interesting patent -- vinyl acetate is available everywhere ... should be nice if it works out..

Sauron - 26-3-2007 at 00:39

I'm not too thrilled with a -8 C flash point though. On the other hand it's not as bad as ether (-30 C) or CS2 (-45 C)

Through the kindness of another member I obtained the following abstract for ref. 4 of the Gulf Research 1962 paper (see above) on PdCl2 catalyzed hydrolysis of vinyl acetate

"Acetylation of isopropenyl acetate catalyzed by mineral acids.
Jeffery, E. A.; Satchell, D. P. N..
Chemistry & Industry (London, United Kingdom) (1960), 1444.

Abstract

The HCl- and HBr-catalyzed acetylation of HOAc to Ac2O was examd. kinetically, the HOAc acting as the solvent so that the deficit of isopropenyl acetate (I) reacted completely. Use of AcOT resulted in negligible labeling of the Me group of the HOAc. Thus the following reaction scheme was preferred: (a) I + HCl -> AcCl + Me2CO (rate-detg. step), (b) AcCl + AcOH .->. Ac2O + HCl (fast), rather than (a) I + HCl -> CH2:CO (II) + Me2O + HCl (rate-detg. step), (b) II + AcOH -> Ac2O (fast), (c) Ac2O + HCl .->. AcCl + AcOH (fast). The AcCl was the real acetylating agent rather than II. Other tracer expts. with H2SO4 catalyst showed that II was not involved in this case either. "



[Edited on 28-3-2007 by Sauron]

Sauron - 27-3-2007 at 19:37

As we are using some unfamiliar terms I thought it would be useful to insert a sketch

Only vinyl acetate is inexpensive.

From structure you can see why isopropenyl acetate produces acetone along with acetic anhydride, rather than acetaldehyde.

[Edited on 28-3-2007 by Sauron]

acetates.jpg - 4kB

chemicalpower - 29-3-2007 at 11:55

i would like to know if someone has tried the vinyl acetate acetic acid sulphuric acid method yet. and if it worked or not

Sauron - 31-3-2007 at 18:03

How did you remove the inhibitor from the VA monomer?

(Did you distill the VA monomer or not?)

And which catalyst did you use? The patent listed many different catalysts. You already told us you can't get good sulfuric acid.

evil_lurker - 31-3-2007 at 19:40

I suppose if one had the balls and could get cylinders of carbon monoxide and chlorine, pass the gasses over a charcoal bed and into acetic acid to form the acyl chloride then proceed from there.

Sauron - 31-3-2007 at 23:54

There has been considerable discussion here about the likelihood that all these industrial processes e,ploying vinyl acetate (VA) were using locally made VA, and that today's commercial VA (which is the monomer) contasins some polymerization inhibitor to keep the VA from turning into PVA polyvinylacetate.

The usual inhibitor is 30-20 ppm hydroquinone. That's 3 to 20 mg per Kg. Not very much. We were not sure if this would be a problem, but it was suggested that a preliminary fractionation would get rid of it.

Also, you want to reflux everything, except the very low boiling acetaldehyde, that you can let distill. Try refluxing at 75-80 C (bp of VA) for 12-24 hrs. If you get no acetaldehyde off, rxn did not go. Also try using 2X the acid catalyst.

This is a famous raction, not just in one patent, but in many articles.

Sauron - 1-4-2007 at 06:10

40-50 C is not reflux, VA boils at 77-78 C. If I were you I'd heat it harder (80 C) and I would increase the catalyst to 10 cc.

Did you get any acetaldehyde or not? Because if you got acetaldehyde you also would have Ac2O. The anhydride would have been last thoing in the pot along with ethylidene diacetate.

What sort of fractionating column are you using?

344 g VA and 240 g AcOH is 4 mols each. Correct ratio.

You should set your column for 100% reflux. If you have any acetaldehyde forming it will flash over, collect it in a colt trap.

If you are making acetaldehyde you are also making Ac2).

[Edited on 1-4-2007 by Sauron]

Sauron - 1-4-2007 at 18:24

Ac2O is acetic anhydride

flash over means distill off rapidly

Acetic acid boils 117

If product boils at 140 is is acetic anhydride

What is left behind is ethylidene diacetate

If you do not use a fractionating coluimn you cannot seperate products.

not_important - 2-4-2007 at 02:40

You need to go to fractional distillation when trying to separate 2 liquids boiling fairly close together, where 'close' means between differing by less than 25 to 50 degrees C., depending.

quick overview
http://www.chemhelper.com/distillation.html

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

bit of theory
http://lorien.ncl.ac.uk/ming/distil/distildes.htm
http://lorien.ncl.ac.uk/ming/distil/distil0.htm

http://www.chemguide.co.uk/physical/phaseeqia/idealfract.htm...

lab scale glassware for 10s of ml to 100s of ml range. Look at entries beginning with 'column' and 'head'
http://www.kimble-kontes.com/html/Distillation_and_Reactors....

commercial equipment
http://www.popeinc.com/fractional_distillation.htm


A nearly 500 page book on the subject, as might be read by a student in chemical engineering who is concerned with the manufacture of products

http://www.archive.org/details/elementsoffracti031055mbp

download the book to read it, don't try to read it in your browser.

You may not need a lot of fractionation, because every cellulose acetylation description I've read uses a mixture of acetic acid and anhydride, so I suspect that some acid in the anhydride you use will cause no problems.

not_important - 2-4-2007 at 06:38

Quote:
Originally posted by hector2000
anybody know NO2 + CH3COONa method?
i think this is easy and cheap.


It's an old patent that doesn't ever seem to have been commercially used. Elsewhere there's been comments that there may be some danger of explosion, if sufficient care isn't taken. And I'd worry about the toxicity of NO2.

The vinyl acetate one is at least related to methods used commercially in the past.

Sauron - 2-4-2007 at 07:00

N2O4 is very toxic just like phosgene and ketene.

Someone else is experimenting with this no, wait and see what he finds out. If it works, calculate how many cylinders of NO2/N2O4 you will need to buy every day to produce the acetic anhydride you need.

For VA method, did you try distilling the VA first to free it of the inhibitor hydroquinone?

No, not that you told us so far.

Did you follow patent instructions and interpose a fractionating column so that acetaldehyde could come off during the 10 hr reflux while all other reactants and products returned to pot?

No, not that you told us.

You said you refluxed at 40-50 C, or was it 50-60 C? Anyway VA boils at 77-78 C so you were not heating enough.

You tried one and only one catalyst out of maybe two dozen possibilities. And you are ready to give up?

You say only VA and acetic acid distill over at end but, you also say temp goes to 140 C and acetic acid boils at 117, so you must have acetic anhydride in the distillate if boiling at 140 C, after all.

But you are ready to give up.

Did you increase catalyst as I suggested? Not that you reported here.

It seems like you do not understand how to fractionally distill, only how to do a simple distillation, and that is not adequate to seperates this mixture.

acetaldehyde bo <30 C will be all gone
unreacted VA bp 77 C
acetic acid bo 117
acetic anhydride bo 140
ethylidene diacetate left in pot

This is not really hard but you do need to know what you are doing to get it right.

Done right, you will see a sharp change in b.p. at top of column

Not a slow gradual climb.

Fractionation is quite slow becausereflux ratio makes it slow.

Sauron - 2-4-2007 at 16:15

I already gave you my advice.

1. Do distill the VA in an attempt to free it from inhibitor.

2. You must allow acetaldehyde to distill during the reaction, you need a cold trap after condenser to catch it.

3. The patent calls for mixture to be rectified, that means fractionated. A simple distillation no matter how slowly you perform it, is insufficient to seperate bp's only 23 C apart.

Sauron - 3-4-2007 at 18:55

This is not directed at hector2000

Please do not email me regarding advice about making Ac2O

Post your questions here so others may respond as well.

There is a vast pool of experience here to be tapped.

My constribution is minor.

@hector, are you measuring the pot temperature (liquid) or the vapor temperature?

It is vapor temperature that is important.

You changed source of VA but, have you distilled the VA or not?

You doubled scale of reaction, but only very slightly increased amount of catalyst, and you haven't tried any other catalyst yet. Try conc HCl. Try conc HBr. Try increasing amount of catalyst 5X or 10X. Mineral acids are cheap.

If you are having trouble getting results but you don't try these things then you are not giving yourself a chance.

[Edited on 4-4-2007 by Sauron]

chemicalpower - 3-4-2007 at 21:17

i am going to try the vinyl acetate method now
i will reflux the mixture at 80 deg c for two hours
and remove the distilled liquid
then i increase the heat to 117 degrees and remove the liquid again
then i increase the heat to 140 degrees and collect the liquid distilled , which should be acetic anhydride.
i am using a fractional distillation column.
and i correct if i am not please correct me
sorry for the email though

chemicalpower - 3-4-2007 at 21:24

i tried the ketene lamp method yesterday. i have built a ketene lamp using copper tubing which is heated from the outside to 750deg c.
but when i pass the gas formed after condensing it through the acetic acid i only get acetic acid and probably acetone liquid which form two layers in the receiving flask.
the two layers are not mixable.
the temperature of the condenser i used is -5 degrees.
the acetone is boiled by putting the flask in boiling water and the copper tube coming from the flask is heated from outside to 750 degrees and then the tube passed through a cold water reservoir where the temperature is -5 degrees. then the tube goes into a receiving flask which has acetic acid in it, the gas is bubbled through the acetic acid .

Sauron - 3-4-2007 at 22:18

I just searched Org.Syn. for reactions involving vinyl acetate, there are 12.

I studied two of them, the first a transesterification and the second formation of vinyl ethers.

It is very noteworthy that in both cases the submitters and checkers purified their VA. In the first case:

2. An Eastman Kodak Company practical grade of vinyl acetate is satisfactory. It was distilled immediately before use through a 48 by in. column packed with 3/32-in. single-turn Pyrex glass helices. The checkers employed material obtained from the Niacet Chemicals Division, Niagara Falls, New York, distilled once through a 12-in. Vigreux column, b.p. 73°/746 mm."

And in the second, the VA was dried over 4A molecular sieves and then distilled in an Argon atmosphere.

I am not suggesting that you must distill under Ar. I am strongly suggesting that you should distill, preferably through a column as described above, and you should seriously consider pretreating with molecular sieves as well.

In a closely related paper regarding the reaction of isopropylidene acetate with acetic acid catalyzed by HCl or HBr the authors identified AcCl (or AcBr) as the active acylating agent in formation of Ac2O.

@hector, given (a) that you have Acetyl chloride and that the contamination with FeCl2 or FeCl3 will not be a problem in the reaction with vinyl acetate, since FeCl2 is named in the patent as a catalyst -- why don't you utizie some of your "contaminated" acetyl chloride and see whether or not it reacts with VA (with or without additional catalyst such as HCl, H2SO4) to produce acetaldehyde and Ac2O?

You probably should mix these slowly and heat cautiously as the reaction may be aggressive. Try on a small scale.


@chemicalpower, you indicated that you would like to obtain 3-4 litera a day Ac2O, but, you sim,ply can't get there via a ketene lamp. A ketene lamp, as I know them, is good for at best half a mol ketene per hour, that means if you run 12 hours a day you might obtainb half a liter Ac2O. So my advice is drop the ketene method, which you are having trouble with anyway.

If you read this thread and several others on acetic anhydride you will find numerous procedures far more productive for the scale you are after.

The vinyl acetate method at present remains unproven in the hands of our members.

Other methods are well proven.

[Edited on 4-4-2007 by Sauron]

not_important - 3-4-2007 at 23:26

I've been searching for my notes from long ago, but with no avail. They may be in storage nearby, or in another country. So what I am saying is from memory decades ago.

There was a time when I needed some acetic anhydride and could not purchase it. I'm not sure why, at that time if I had wanted I could have bought 1-phenyl-2-propanone, go figure.

I research and tried a number of the methods listed in the journals and patents as ways to produce acetic anhydride. Many didn't work that well, the industrial methods of acetic acid pyrolysis (actually a ketene route) and a number in the acetylene pathway including ethylene diacetate base ones and others based around vinyl acetate (but not the one Sauron has recently described) all tended to have a few percent of coloured condensation products formed, a bother to clean up; some had poor yields on the scale I could do. The various methods based around halogens and sulfur were more trouble than I wanted to deal with, some were tricky if you wanted to avoid an impure and difficult to cleanup product, some were tough to get consistent yields with.

I ended up going with the hot tube route, the classic ketene lamp was too much glassblowing and a bit lower capacity than I wanted. I picked it partly because acetone was cheap and easy to get, partly because it could do other useful reactions besides making acetic anhydride.

I knew someone who did plant wielding and would do wielding and brazing for me. All the of the hot joints in my system were brazed; the system was checked to hold 3 atmospheres of pressure for several days, through repeated heating and cooling cycles. I pressure checked the unit before each use. As I was doing noting illegal, I had no worries about authorities coming around checking up on this pile of tubing I was assembling.

Unreacted acetone was condensed and returned to the boiler. The unit would process a liter or two of acetone an hour, with an estimated 1/4 converted to ketene (measured by formation of sodium acetate, acetamide, ethyl acetate, acetic anhydride, and acetanilide.) The higher feed rates took more babysitting so I tended to stick with 1 to 1.25 liters/hr.

I ran t he hot tube at 600 to 650 C. It is important to have the proper flow rate of acetone vapour through the tube. Too fast means little conversion to ketene, too slow means too much of the ketene decomposes to carbon monoxide and ethylene. It is important that the gases inside the tube are well mixed, experiencing turbulent flow, otherwise less acetone is converted and the ketene formed near the walls may excessively break down. Unevenheating of the tube has the same effect, hot spots must be avoided. The gases exiting the tube must be cooled quickly, otherwise ketene will decompose.

It took awhile to get it all to work correctly. I had to redo the condensers when it turned out they were failing to condense too much of the acetone.
Quote:
i only get acetic acid and probably acetone liquid which form two layers in the receiving flask. the two layers are not mixable.


Did you check to see if acetone and acetic acid are miscible? What is the apparent boiling point of each of those layers? What are their densities? Try treating a little of each layer with dilute permanganate and see what happens.

Sauron - 4-4-2007 at 01:49

OK @hector, now what reaction was this?

VA and AcOH?

or VA and AcCl?

And which proportions, catalyst and time?

See if you can measure boiling point. You say density < 1.0 and immiscible with water?

By the way, acetic acid and acetone are 100% miscible. However, there should not be any acetone around, only acetaldehyde possible and it would have flashed off at the start.

Sauron - 4-4-2007 at 09:06

All right, @hector, so this was VA and acetic acid with H2SO4 (Merck) as catalyst.

It will be some time (weeks) before I can try this reaction myself as I must order in VA from outside Thailand. Maybe another member can try it.

In any case I advise:

1. Use freshly distilled vinyl acetate only, by one of the procedures described above taken from Org.Syn.

I found another Org.Syn pre where they did rxn with and without distilling their VA. Without distilling the product was contaminated with poly(vinyl acetate) as a yellow gunk. With distillation they got a better yield and higher purity of product.

2. Follow patent procedure, particularly in regard to stripping acetaldehyde during 10 hr reaction through fractionating column, then fractionating the reaction mixture. The reaction mixture should include 77% Ac2O, balance unreaccted AcOH and VA, and a little high boiling ethylidene diacetate.

VA bp 77-78 C
AcOH bp 117-118 C
Ac2O 140 C
ethylidene diacetate will remain in pot.

@hector, after reading your second post:

Your VA should distill at 77-78 C.

I think if it distills at 105 it is polymerized already.

Therefore use only the VA from first source (this is from second source right?)

And check bp of that one as well.

Distill your VA before using it (only as much as you will use.)

If possible, distill it in vacuum or, under N2 or Ar inert atmosphere.

Only possible source of sulfur is H2SO4, hydroquinone inhibitor is reducing agent but I am not familiar with it reducing sulfuric acid which is quite a trick!



[Edited on 5-4-2007 by Sauron]

Endo - 4-4-2007 at 09:28

Quote:
Originally posted by hector2000
i am confuse :o
when i test my vinyl boiling point it was 105 deg.
and another interesting matter is red color of reaction.
in this reaction when i add vinyl to acetic and sulfuric the color of mixture begin to change and first turn to yellow and then red.
there is unknow componet in my balloon(after distil) that has h2s favour.
therefore there is question in my mind:why my vinyl acetate boiling point isnt true?
you think this is inhibitor effect?


Was your balloon Latex?

If you have ever sprayed an acidic solution onto latex you typically smell some H2S like scent from the acid releasing the vulcanizing agent from the rubber.

chemicalpower - 4-4-2007 at 11:53

i tried the vinyl acetate method and got somewhat similar results as hector.i first distilled the vinyl acetate.
i mixed the correct proportion in acetic acid , vinyl acetate and sulphuric acid.the colour of the solution turns red.thenfirst i heated untill the temperature at the top of the fractionating column was 40degrees. i did get some clear liquid after the condenser, i assume it was aldehyde.
the smell was sweet and like rotting fruits.
then i increased the heat to 80degrees and another clear liquid came out after the condenser, i assume it was vinyl acetate. a little blueish in colour.
then i increase the heat to 105 degrees and another clear liquid came out which was supposedly acetic acid.
then when i increased the heat to 120degrees a little liquid came out but the smell and action in a water glass was not like acetic anhydride, it was more like acetic acid.
so where am i wrong.

Sauron - 4-4-2007 at 19:43

The patent calls for refluxing the mixture for ten hours, and using the fractionating column during that period to strip off ONLY the acetaldehyde formed. Everything else refluxes, that is, whatever boils up is condensed in a vertical condenser of high efficiency and returns to pot.

ONLY AFTER ten hours of relux, at whatever temperature is required to maintain boiling, and no more, do you shift setup for downward distillation, still through fract. column, and SLOWLY fractionate the mixture.

That means you first take a few hours to allow column to equilibrate at 100% reflux, collecting NO product.

Then you set reflux ratio to about 10:1 which means 10 drops reflux for every 1 drop that you collect, and start collecting product, noting temperature at still head. You should first get unreacted VA 77-78 C.

Then temperature should rise (OF ITS OWN ACCORD) to 117 C and acetic acid should come over. IF you need to increase heat to get this to happen you must return to 100% reflux till system re-equilibrates (several hours) before you can start collecting again.

Once all AcOH is off, what remains should be mostly Ac2O and will distill at 140 C.

Once again, if you need to up your heat, re-equilibrate.

Fractionating is SLOW, you guys are forcing distillation and guaranteeing a poor seperation.

Read the book on fractionation PLEASE.

Also, before you do anything else, distill your VA and if it does not distill at 77-78 C you know you have a problem. Stop and fix that problem -- get good VA -- before you do anything else.

chemicalpower - 4-4-2007 at 21:41

i have read the paper on fractional distillation. the problem is i have made my own column from copper tubing 25mm dia and placed glass bead in it . fitted a ditial temperature sensor at the top
you are right i didnt wait 10 hours for reflux and condensing the aldehyde just maybe 30 min
but please tell me . i am heating the mix on an electric heater and the temperature i can keep at 80 to 90 deg but how will it rise to 140 then.i

chemicalpower - 4-4-2007 at 21:47

how do i re equiblibrate the column

not_important - 4-4-2007 at 22:07

Quote:
Originally posted by chemicalpower
how do i re equiblibrate the column


Just as you do the first time, quoting Sauron
Quote:
That means you first take a few hours to allow column to equilibrate at 100% reflux, collecting NO product.

Then you set reflux ratio to about 10:1 which means 10 drops reflux for every 1 drop that you collect, and start collecting product, noting temperature at still head.


Fractional distillation without automatic controls is rather tiresome.

By the way, you will likely need to insulate your column to reduce heat loss.

Sauron - 4-4-2007 at 22:15

Assuming that boilup rate is correct and stable so that the column does not flood, and that the column is well lagged (insulated, vac.jacketed, or temp.controlled) then all you do is kick back and wait and the column will equilibrate itself.

At that point the lowest boiling component will be at the top of column and the highest boiling component at bottom (or still in pot) and you can slowly ease off the 100% reflux and start collecting product, SLOWLY so as not to disturb that equilibrium, upon which the good seperation depends. Watch your themometer at the still head, cut your fractions accordingly.

Remember this is a slow tedious process. If you rush it you mess it up. When you distill with ten theoretical plates you are effectively doing 10 simple distillations but the price you pay is it takes about 10X as long!

not_important - 4-4-2007 at 23:40

If your column is very long it is worthwhile making sure that it is truly vertical, so that the reflux flows equally over all the packing. If the column is slanted so that most of the reflux flows down one side you are reducing the interaction between reflux and ascending vapour which reduces the effectivity of the column.

chemicalpower - 5-4-2007 at 04:54

wow now how do i get a fractional distillation column with automatic controls
where i am they hardly know about the fractional distillation . that is why i had to make one of my own from copper tube one inch dia., filled it with glass beads upto 3/4 length and placed a thermometer at the top end

Sauron - 5-4-2007 at 05:38

I fear that you will find that acetic acid will eat your copper tube column very very happily.

No one was talking about automatic controls.

The suggestions were to insulate column, or vacuum jacket it, or regulate the temperature along the outside oif the column. Only in the final case (in which the column is rather like a jacketed condenser but with a support for the packing) you may or may not employ temperature regulating electronics and thermocouples. The first two methods are more typical.

not_important - 5-4-2007 at 05:48

I'd mentioned automatic controls, just in passing as a warning that fractional distillation takes a lot of attention and time; especially true for new hardware and set of compounds being distilled.

I struggle through distillations on my own, as most people do. More automatic gear is worthwhile in production environments..

Sauron - 5-4-2007 at 06:04

Yes I wish I wish I could afford a nice PC-controlled, fully instrumented Teflon spinning band still with 200 tp's but, so far at least I have resisted all temptation to invest $5000 in such a system, even though that price (second hand) is not soo bad for what it is.

You must appreciate that a still like that has a throughput of only a few ml's an hour.

Most fract. stills clunk along at 5-30 tp's but have somewhat more real world throughputs.

I instead put most of my mad money into HPLC, which gives me thousands of tp's and (with prep systems like mine) can handle multiple gram samples (or 10-20 g samples with slightly larger systems) and can seperate liqids and solids. And if you want to talk state of the art, can seperate enantiomers and diastereomers if you can stand the price of a chiral column! Try that with a still.

Sauron - 5-4-2007 at 06:56

You are right, the patent teaches merely to fractionate off the acetaldehyde formed while refluxing all else, until no more acetaldehyde is obtained (signalling completion of reaction.)

However, so far, you have not recovered ANY acetaldehyde at all, as far as you have said. Until you do, which will require a fract.column and a cold trap (not just a condenser) I think you can conclude you haven't gotten this reaction to work at all.

No acetaldehyde = no acetic anhydride.

---------------------

If you read the patent carefully you will note that the inventor prominently mentions the alternative method of conducting the reaction in vapor phase, by passing the vaports of VA and acetic acid over the heated catalyst (hint: solid catalyst selected from his long list of catalysts) then condensing. This is usually done in a horizontal combustion tube with catalyst in a "boat" but other arrangements are possible. In processes of this type, you play with the dwell time of the vapors over the catalyst as they progress through the tube as well as the catalyst temperature (which should be higher than the bp of Ac2O, let's say 150-200 C).

You could do this with a liquid catalyst by bubbling the vapors through a wash bottle containing the catalyst (say H2SO4) held at >150 C so that all reactants and products stay in vapor phase.

Solid catalysts mentioned are zinc chloride, mercuric sulfate, and sodium bisulfate. Liquid catalysts: sulfuric acid, phosphoric acid, sulfoacetic acid, benzenesulfuric acid, and sulfur chloride. The only gaseous catalyst mentioned is Cl2.

"Benzenesulfuric acid" is benzenesulfolic acid, and I would assume that p-toluenesulfonic acid would do as well. Sulfoacetic acid is unfamiliar, I will have to look it up. Okay, it is HSO3CH2COOH.

Sulfur chloride is ambiguous and could be SCl2 or S2Cl2 both liquid and nasty.

[Edited on 6-4-2007 by Sauron]

[Edited on 6-4-2007 by Sauron]

chemicalpower - 5-4-2007 at 09:39

i am going to put a heat insulation around the column tomorow and try again , by the way the aldehyde form with conc HCl and not with sulphuric acid. i hope this method works
meanwhile i am still confused as why didnt my ketene method work
i heated the acetone and then passed it through a copper tube which was heated from outside to 700 degrees , i got some liquid after distillation and milky white gas formed in the receiving flask. but at the end i had two layers of non mixable liquids , one smelled and behaved like acetic acid and the other i think was acetone maybe . but if acetone and acetic acid are mixable then what did i get and how

Sauron - 5-4-2007 at 09:59

@hector, take heed. Try conc hydrochloric acid instead of sulfuric acid. @chemicalpower said that this got him acetaldehyde, and that should mean he also made Ac2O

The patent does not mention hydrochloric or hydrobromic acids but, other sources about this reaction do. And they are strong mineral acids which the patent does mention.

--------------

Way back two pages of this thread ago I posted the following:
Through the kindness of another member I obtained the following abstract for ref. 4 of the Gulf Research 1962 paper (see above) on PdCl2 catalyzed hydrolysis of vinyl acetate

"Acetylation of isopropenyl acetate catalyzed by mineral acids.
Jeffery, E. A.; Satchell, D. P. N..
Chemistry & Industry (London, United Kingdom) (1960), 1444.

Abstract

The HCl- and HBr-catalyzed acetylation of HOAc to Ac2O was examd. kinetically, the HOAc acting as the solvent so that the deficit of isopropenyl acetate (I) reacted completely. Use of AcOT resulted in negligible labeling of the Me group of the HOAc. Thus the following reaction scheme was preferred: (a) I + HCl -> AcCl + Me2CO (rate-detg. step), (b) AcCl + AcOH .->. Ac2O + HCl (fast), rather than (a) I + HCl -> CH2:CO (II) + Me2O + HCl (rate-detg. step), (b) II + AcOH -> Ac2O (fast), (c) Ac2O + HCl .->. AcCl + AcOH (fast). The AcCl was the real acetylating agent rather than II. Other tracer expts. with H2SO4 catalyst showed that II was not involved in this case either. "

Now, you can ignore the difference between vinyl acetate and isopropenyl acetate, which is only a Me group and the result that byproduct is acetone not acetaldehyde. The reaction is the same. The main product is Ac2O, and the catalyst is conc HCl or conc HBr. The mechanism is explained above. Ignore the stuff about II (ketene) because they proved it is NOT involved.

So, this paper supports @chemicalpower's result.

The rate determining step is formation of AcCl. That results from chlorination of the ester, in this case by HCl itself. The second step is formation of Ac2O from AcOH and AcCl, with regeneration of catalyst HCl.

CONCLUSIONS

1. DROP H2SO4 and instead use HCl or HBr

2. AcCl (which you buy from Merck) will react with VA to give you Ac2O and acetaldehyde.

You can do that catalytically (AcCl as catalyst) or directly.

3. Other catalysts that efficiently make AcCl from AcOH will work great in this reaction. SCl2 or S2Cl2 mentioned by patent. PCl3, PCl5, POCl3, SOCl2. SO2Cl2.

4. I bet anhydrous solutions of HCl or HBr gas in AcOH will work well.

5. PBr3 should work very well. Red P and a little Br2 same.

NaBr and H2SO4 to make HBr in situ, ought to work well.

The key is making AcCl in situ and then the AcCl replenishes the reagent that made it. Hence catalysis.

As the rate determining step is reversible it helps to efficiently remove the aldehyde as it is formed, fortunately its low bp facilitates this.

[Edited on 6-4-2007 by Sauron]

VA.jpg - 8kB

Sauron - 6-4-2007 at 01:13

I advise that you use conc hydrochloric acid in place of H2SO4

I advise you to distill your VA first, and to use a cold trap with a freezing mixture (like ice/salt) to trap the acetaldehyde formed, because the amount of acetaldehyde formed will tell you how much anhydride was also formed.

I am considering the possibility that AcCl will react with AcOH (instead of NaOAc) to give Ac2O, I am just wondering if an acid trap like TEA pr pyridine is needed to snap up the Hcl as it if formed.

Perfect your VA reaction first and don't worry about the other till later.

Sauron - 6-4-2007 at 02:55

Try reading the posts and you might understand.

I even drew you a diagram.

The reaction is in TWO STEPS

In the first step, VA is cleaved by HCl into aldehyde and acetyl chloride.

In the second step, acetyl chloride and AcOH react to form anhydride.

THEREFORE...do I have to spell it out for you?

You already know, AcCl and NaOAc works because you have done it. Where does the HCl go? Into NaCl.

So all I am considering is, in rxn of AcCl and AcOH, in absence of catalyst, what is fate of HCl? Need we bind it up in a scavanger or not?

chemicalpower - 6-4-2007 at 05:40

ok lets suppose we seperate the aldehyde from the vinyl hcl mixture. and we are left with acetyl chloride. then how much acetic acid do we put in , and then how do we seperate the hcl formed from the acetic anhydride

Sauron - 6-4-2007 at 08:06

Try reading them AGAIN.

chemicalpower - 6-4-2007 at 08:16

ok can i just use the acetyl chloride formed with sodium acetate anhydrous to make acetic anhydride
i tried reading again and again
what are the scavenger named for hcl

Sauron - 6-4-2007 at 21:17

@chemicalpower:

The two stage reaction scheme is a MECHNISM for the overall reaction, not a PROCEDURE.

The PROCEDURE is done as a single step.

When you see language like "rate limiting step" you know (if you are a chemist) you are looking at a MECHNISM. Understanding the mechanism helps you understand the procedure.

If as you say you obtained acetaldehyde when you used HCl with VA and AcOH then you also obtained Ac2O

If you tell us how MUCH acetaldehyde you obtained (by coldtrapping it and weighing it or measuring it) then you will know how much Ac2O you have in your pot and then you just have to fractionate it.

@hecor, how many years of research do you want to invest in the two untried methods you proposed?

If you are unhappy with vinyl acetate after a miniscule amount of time and effort, go back to the sodium acetate and acetyl chloride and solve your contamination problem with the acetyl chloride which really ought to be as simple as rebottling the stuff into glass without letting it touch the steel drum. You have a nonmetallic drum pump I assume. Get some 10L or larger lab bottles and use them. Or compatible plastic carboys. Suppliers: Schott/Duran, Nalgene.

not_important - 6-4-2007 at 21:58

Quote:
Originally posted by hector2000
i have two question
1-may anhydrid make if we electrolysis the acoh?
(before i read the patent that the electrolysis of sulfuric acid will make oleum.i think this will be true for acetic acid)


No. Many reactions occur, see Kolbe Electrolysis for one important one. In most cases decarboxylation of the acid occurs .
Quote:

2-may anhydrid make if we react methyl acetate with acetyl chloride?


One way to make methyl acetate is to react methyl alcohol with acetyl chloride, what does this suggest to you? You can make your proposed reaction work, I believe, but it requires somewhat extreme conditions and precious metal catalyst.

[Edited on 7-4-2007 by not_important]

Sauron - 7-4-2007 at 01:21

When the man says extreme conditions he means thousands of atmspheres pressure and high temperatures, meaning millions of dollars (probably tens of millions) investment and you aren't going to do that for 50 liters a day. @hector, you framed your problem as 30-50 L a day required. That isn't even pilot scale, that is large bench scale.

You have a workable process with acetyl chloride you buy cheap in volume and sodium acetate you dry in bulk.

You have a small essentially mechanical problem (materials handling problem) with the AcCl reacting with steel drun once the PE liner seal is broken, I told you how to deal with that (repack in glass or HDPE)

You are looking for a cheaper process to replace AcCl/NaOCl.

The only process that has come up that offers you any hope is VA/AcOH/catalyst.

Someone (me or someone else) who is properly equipped needs to procure and distill some VA and carry out this reaction properly to determine the conditions that work. @chemicalpower says conc HCl works for him while conc H2SO4 does not. I think conc HBr is a very good bet as is PBr3, red P/Bromine, S/bromine and so on. I have requested quote for VA and hope to find some locally so I can get this done soon.

The patent is rather broad, as it encompasses reduced pressure, positive pressure, as well as normal pressure conditions as well as vapor phase and mixed-catalyst possibilities. It also mentions lots of catalysts you have not tried. But at present, based on the literature and on what @chempower says, halogen mineral acids look loikely as do related substances that give rise to AcCl/AcBr.

Sauron - 8-4-2007 at 10:30

A ketene lamp will never get you more than half a mol ketene per hour and probably less.

That means if you run it 12 hours a day you make 6 mols or about 500 g Ac2). But you don't want half a liter a day you want 100 times that much. Do you propose to operate 100 ketene lamps? Because you cannot scale up a ketene lamp.

24 gauge wire is #24 on the Brown and Sharpe wire gauge.

There are more than one ketene lamp article and patent, some describe nichrome wire some platinum wire.

But it does not matter because for your purpose ketene lamp is only a toy and you need a larger scale process.

You need to make 50 mols ketent an hour not 0.5 mol. That is a LOT of ketene and ketene is DANGEROUS. In short this is a very bad idea. I have told you this before, and others have told you this before. You are going to hurt yourself badly making such a qty ketene. Forget it. I cannot help you in this.

chemicalpower - 8-4-2007 at 11:13

ok now i tried the vinyl acetate hcl method. about three times with my home made apparatus
i got acetic anhydride twice and failed once.
but some observations.
1) the acetaldehyde i got has a slight greenish colour.
2) the acetic anhydride that i got has a yellow brownish colour and the quantity is pretty less
i used 370cc of vinyl acetate and distilled about 210cc of aldehyde in 3 hours time.
then i mixed the acetylchloride obtained with sodium acetate, as i didnt know the exact quantity to put in i used about 150grams of sodium acetate for the approx 150cc acetyl chloride. i started distilling the contents to extract acetic anhydride
but then again i got some acetaldehyde and a very little quantity of acetic anhydride.
i need some help here like
1) why is the colour of aldehyde greenish
2) why is the colour of acetic anhydride yellow brown.
3) how much sodium acetate do i use and do i need to heat it prior.
4) how do i extract the anhydride from the mixture, as it forms sort of a past.

not_important - 8-4-2007 at 11:48

Quote:
Originally posted by chemicalpower
...
1) why is the colour of aldehyde greenish
2) why is the colour of acetic anhydride yellow brown.
...


You are using the copper tube column? If so expect copper salts to be formed in the presence of acids and oxygen/air.

Sauron - 8-4-2007 at 19:09

That is correct, you are making some copper acetate and soon you will have holes in your column.

Replace with pyrex column. Green color will go away.

Quantity of aldehyde produced is correct per patent.

However, you say you took the acetyl chloride formed and then reacted it with NaOAc.

Two points: you never should have been able to isolate acetyl chloride because as soon as it forms is reacts with AcOH (fast) and produces Ac2O

You should have (once no more aldehyde came off) fractionated the mixture, obtaining first a little unreacted VA, then unreatced AcOH again not much, then your Ac2O. pot residue would have been a little ethylidene diacetate and some polyVA and tars.

Other point is that if you obtain or make acetyl chloride and want to react it with sod.acetate, the acetate must be rigorously anhydrous, if not the water of hydration reacts with AcCl/Ac2O and produces only AcOH.

You can buy superdry grade of the acetate salt, or you can fuse your ordinary acetate salt, or you can go belt & suspenders and do both. But if you don't your yield will be low.

If you have succeeded with VA reaction congratulations, because if you collected 210 ml acetaldehyde you would have about 400 ml Ac2O in your pot and no AcCl. You just need to seperate it from VA, AcOH, etc.

chemicalpower - 8-4-2007 at 21:13

yes you are correct. but i modified the stuff a bit and didnt use acetic acid at all
i just distilled the VA first then put in the acid , then distilled the aldehyde off and what was left was acetylchloride. is that correct .
then i took the acetyl chloride and mixed with sodium acetate to give acetic anhydride

Sauron - 8-4-2007 at 21:38

Well, no, that is NOT correct.

You are trying to use the MECHANISM I posted as if it is a PROCEDURE but it is now seperable into two discrete procedural steps.

Under conditions you describe you will obtain very little acetyl chloride because in absence of AcOH the regeneration of HCl can't take place and therefore the amount acetyl chloride will be same as amount of HCl you put in. Catalysis wll not occur.

If you want to react acetyl chloride with NaOAc, fine and dandy, that works (as long as the acetate is anhydrous).

You prepare acetyl chloride from acetic acid and TCT (CC) cyanuric chloride.

Much has been posted here about this. There are other ways to make acetyl chloride but they are harder and require reagents harder to buy.

chemicalpower - 9-4-2007 at 09:56

ok i suppose i misunderstood the mechanism .
i will try it out again tommorow.
i will this time do the complete reactions and use acetic acid. lets see how it works

chemicalpower - 9-4-2007 at 10:20

i will try out the whole process tomorow but just for the sake of understanding it, i want to ask what if i use a lot of hcl with the vinyl acetate, since you said i will get the same amount of anhydride as the acid i put in . lets suppose i put 200cc of hcl in 370cc of vinyl acetate , how much acetylchloride will form.

chemicalpower - 9-4-2007 at 10:22

i will try out the whole process tomorow but just for the sake of understanding it, i want to ask what if i use a lot of hcl with the vinyl acetate, since you said i will get the same amount of anhydride as the acid i put in . lets suppose i put 200cc of hcl in 370cc of vinyl acetate , how much acetylchloride will form.

Sauron - 9-4-2007 at 11:53

It's purely speculative. Do you see any examples from the literature of preparation of acid chlorides this way?

No.

I told you already, you can't take half a mechanism and turn it into a preparative procedure with much expectation of success.

The reaction you propose would be reversible and would be as likely as not to go nowhere. If you think otherwise, try it and see for yourself.

The literature says you can make acetic anhydride and acetaldehyde from VA and acetic acid with certain catalysts.

The literature also says you can make vinyl acetate from acetaldehyde and acetic anhydride with certain catalysts.

What you are talking about is terra incognita.

My advice, once again, is that if you want to prepare acetyl chloride, do so one of the well proven ways and be done with it.

I was under the impression that you only want it to make Ac2O 3-5 L/day for whatever your real purpose is, so wgy should you spin your wheels trying untested undocumented and MISUNDERSTOOD methods instead of reliable and proven ones?

Because clearly you misunderstood what I posted and that does not speak well for your abilities.

I don't mean to be rude but, I am getting tired of having to repeat myself.

[Edited on 10-4-2007 by Sauron]
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