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chemicalpower
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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
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Sauron
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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.
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not_important
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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..
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Sauron
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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.
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Sauron
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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]
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chemicalpower
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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
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Sauron
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@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]
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Sauron
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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.
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Sauron
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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?
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chemicalpower
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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
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Sauron
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Try reading them AGAIN.
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chemicalpower
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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
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Sauron
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@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.
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not_important
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| 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?
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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]
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Sauron
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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.
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Sauron
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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.
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chemicalpower
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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.
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not_important
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| Quote: | Originally posted by chemicalpower
...
1) why is the colour of aldehyde greenish
2) why is the colour of acetic anhydride yellow brown.
...
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You are using the copper tube column? If so expect copper salts to be formed in the presence of acids and oxygen/air.
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Sauron
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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.
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chemicalpower
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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
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Sauron
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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.
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chemicalpower
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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
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chemicalpower
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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.
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chemicalpower
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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.
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Sauron
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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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