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Author: Subject: keten lamp
chemicalpower
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[*] posted on 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
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Sauron
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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]
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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]
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[*] posted on 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
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[*] posted on 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 .
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[*] posted on 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]
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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]
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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
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[*] posted on 4-4-2007 at 21:47


how do i re equiblibrate the column
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[*] posted on 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.
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[*] posted on 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!
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[*] posted on 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.
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