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Sauron
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Got an autoclave?
Because 40 C is quite a bit higher than the bp of acetaldehyde. In fact it is just about DOUBLE the bp, which is 21 C.
You'll lose it all through the condenser.
So without a pressure vessel, testing is going to be tough.
[Edited on 17-11-2008 by Sauron]
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ItalianXKem
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heat a aqueous solution of acetic acid and hydrogen sulfate (vitriol , car battery acid , sulfuric acid) H2SO4 , don't try this at home , is very
dangerous , this synthesis can be make only a expert chemister
2 CH3COOH + H2SO4 ---heat---> (CH3CO)2O , evaporates H2O
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Sauron
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Sorry, that will not work. I challenge you to provide supporting chemical literature references that claim it will.
Any aqueous solution will fail, and >100% H2SO4 (oleum, fuming H2SO4, free SO3 dissolved) will chew acetic acid up to CO2 etc under the conditions
you describe.
Try again.
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ItalianXKem
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doh ! 
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Formatik
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Heating a mixture of AcOH with conc H2SO4 causes it to discolor and develop SO2 and CO2 gases in varying amounts. If one uses oleum in excess, then it
heats up by itself and without evolution of gases, heating it stronger develops nearly pure CO2, which has barely 5-10% SO2. And SO3 solubilizes in
AcOH without evolving any gases, and this is destroyed by water; heating this forms sulfoacetic acid. Source: Lehrbuch der organischen Chemie,
Gerhardt, Wagner, p. 805. It was a nice theoretical idea, but in reality is wishful thinking. I believe the idea was discussed a few pages back.
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Sauron
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Quite right, formatik. Full marks. This scheme will not succeed no matter how expert the "chemister" may be.
The lit. on sulfoacetic acid is instructive.
Once again I recommend Roger Adams in JACS circa 1916-1919 regarding dehydration of carboxylic acids to anhydrides using oxalyl chloride. Depending on
ratio of reactants one can cleanly obtain the anhydride or the acyl chloride. The mechanism is elucidated for both cases. Too bad the reagent is so
costly (and nasty) or this would be a productive method. It still can be if you make your own oxalyl chloride (from anhydrous oxalic acid and TCT
(cyanuric chloride) but, the nastiness is still there, and a lot of people seem unable to obtain TCT. Oh well. But there are many viable alternatives.
I mention this one simply because it is one of the few examples of going straight from the acid to the anhydride without proceeding via the acyl
chloride first.
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hector2000
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| Quote: | Originally posted by quarterfinal
i have been trying out the vinyl acetate method mentioneed in earlier threads and have succeeded in getting acetic anhydride . but the yield and
purity are pretty bad. the yield is about 10% and the purity is about 60% or max 70%. there is a lot of acetic acid mixed with the product and its
pretty hard to seperate with even careful fractional distillation. |
may you explain your ratio?
before i try this method and i got nothing
[Edited on 15-12-2008 by hector2000]
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chemrox
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triazine method
There are 21 pages of this thread and so I haven't looked page by page to see if anyone posted the Na2CO3-SOCl2 method> It is simple and
efficient. There is also a hydroxy 1,3,5 triazine method where the solvent ratios of DCM and 3-methyl morpholine have to be 1:1 ..odd.
Attachment: a triazine-e.g. DCMTw-a morpholine.pdf (110kB)
This file has been downloaded 1287 times
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Engager
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Acetic anhydride from thionyl chloride
Round bottom flask (500 ml) is filled with 144 ml of thionyl chloride and 120ml of glacial acetic acid is added with
stirring. Reaction starts immediately, evolving steady stream of sulfur dioxide and hydrogen chloride bubbles. Process is strongly endothermic and
causes strong cooling of reaction mixture, shortly after start reaction mixture separates to 2 layers. Reaction flask is left for 2 hours, allowing
contents to heat slowly to room temperature (#1). Then lower layer of thionyl chloride will completely disappear, reaction flask is attached to reflux
condenser and is heated on 60C water bath for 2 hours, after witch no more gas is evolved from reaction mixture. Mixture is chilled in cold water and
160g of freshly fused sodium acetate is added in portions with intense stirring (#2). After all sodium acetate is added reflux condenser is reattached
and mixture is allowed to sit on hot water bath for 2 more hours. Formed slurry is gently mixed and reaction mixture is distilled on wax bath, to give
130-140 ml of acetic anhydride with 65-70% yield (#3).
Notes:
1. Reaction goes rapidly even at low temperature, and slow heating to room
temperature (for 2 hours) prevents process from becoming to violent. Lower layer of reaction mixture (thionyl chloride) diminishes rapidly during
course of reaction, forming SO2 and HCl bubbles on it’s border. After lower layer completely disappears gas evolution slows down, and mixture
must be heated further to force reaction to complete.
2. This reaction step requires anhydrous sodium acetate to be used, it can be
prepared by gentle heating of commercially available hydrated sodium acetate. This freshly fused sodium acetate is ground to fine powder and used
immediately. Addition of sodium acetate cause heating, because reaction at this step is exothermic addition rate must be adjusted, not allowing
temperature to rise above 45C to prevent boiling and evaporation of highly volatile acetyl chloride (boiling point 51.8C).
3. Practical yield of acetic anhydride then using distillation at normal pressure
is remarkably lower then theoretical (130-140ml), due to high absorption of product in solidified sodium chloride mass. To aid evaporation of residual
acetic anhydride, solid is crushed by glass rod and rest of product is distilled under vacuum. Use of vacuum distillation allows to obtain product in
yield close to theoretical (185-190 ml, 92-95%).
First photo shows pure thionyl cloride, addition of glacial acetic acid start endothermic reaction, resulting in strong cooling of reaction mixture.
Cooling is so remarkable that water condensate on outer surface of reaction vessel freezes into layer of ice.
After ice is remelted it's clearly seen that some thionyl chloride is separated to form new layer at the bottom of the flask. Layer deminishes slowly
entering the reaction, and steady stream of SO2 and HCl bubbles are comming from upper border of this layer. After mixure is allowed to stand at room
temperature, thionyl layer disappears completely and gas evolution slows down, further heating on water bath at 60C is required to force reaction to
complete.
Sodium acetate, used for this synthesis must be completely anhydrous, and can be obtained by gentle heating of commercialy avialable hydrated sodium
acetate. Hydrated sodium acetate is heated on metall dish, shorty after heat applied salt dissolves in it's own crystallization water and forms liqiud
solution, witch loses water on furher heating and dehydrated salt is sollidified, however to ensure full removal of water heating is continued until
salt finaly remelts at ~321C. Anhydrous acetate is grounded on cooling and is used imidately.
Addtion of sodium acetate causes exothermic reaction, so it must be added by portions with gentle mixing, not allowing mixture to heat above 45C.
After adition is complete, reflux condenser is connected and mixture is allowed to sit on hot water bath for an hour or two to ensure complete
reaction. At the end of this period mixture forms hardly stirable slurry, witch is distilled on wax bath to get reaction product - acetic anhydride.
There are also 2 video files avialale:
1. Reaction of thionyl chloride with glacial acetic acid (link).
2. Distillation of acetic anhydrige from reaction mixture (link).
[Edited on 26-3-2009 by Engager]
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Sauron
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You will be better off starting with commercial anhydrous NaOAc rather than the trihydrate. The trihydrate requires a two stage fusion and the second
stage is easy to screw up.
Also there are far far better chlorinating reagents than SOCl2 for this application.
Some details you omitted
SOCl2 FW 118 d 1.63
AcOH FW 60 d 1.04
So you ran this on a 2 mol scale using stoichiometric SOCl2 rather than the usual excess, this gets around Vogel's objection to use of SOCl2 to
chlorinate C2 and C3 acids. And you did not isolate and purify your AcCl. With the nodification you describe you appear to have gotten excellent yield
anyway.
Lots of us still cannot buy SOCl2 and must either mmakes our own or use another reagent.
[Edited on 26-3-2009 by Sauron]
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no1uno
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Sauron, have you any ref's on using oxalyl chloride to generate AA? Rhodium has the prep'n of oxalyl chloride from PCl5 (which rather simply avoids
the alpha-chlorination problem encountered using RP on GAA directly if you do).
| Quote: | Preparation of Oxalyl Chloride
126g (1 mole) of anhydrous oxalic acid is ground into a fine powder and mixed slowly and thoroughly with 400g (1.92 moles) of powdered phosphorous
pentachloride (PCl5) with efficient cooling in an ice bath. Chlorine gas is evolved, so it is important to perform the reaction under an efficient
fume hood. The mixture was allowed to return to room temperature slowly, and was left standing for 48-72h until the mixture liquifies completely. The
mixture is now distilled, collecting the fraction boiling between 60-100°C. Repeat the distillation until the phosphorus-free, pure oxalyl chloride,
bp 63-64°C, is obtained. Yeild approximately 45-50% of theoery. Fractional distillation would most likely allow a quicker separation but the author
made no mention of this.
Reference: Staudinger, Ber., v41, p3563 (1908) (taken from: http://designer-drugs.com/pte/12.162.180.114/dcd/chemistry/o...) |
What would be the fate of the phosphorus pentachloride? Phosphoryl chloride perhaps? If so, both could be used directly from that point couldn't they?
On a more practical note, do you still have the reference (mentioned or more properly alluded to, upthread) where the method of Tarbutton, et al, was
elucidated in greater detail? Tarbutton's work was nice to read, but something with more details on the chlorides would be grand.
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Sauron
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First of all forget Rhodium.
If you work out the mass balance you will quickly see that it takes a great deal of PCl5 to chlorinate a little anhydrous oxalic acid, even
theoretically, and since the actual yield is 50% or less, this only gets worse not better. The reaction is a great way to make POCl3 and a crap way to
make oxalyl chloride.
So forget it.
Roget Adams, that is the great Roger Adams, founding editor of Organic Syntheses, and Organic Reactions, etc. published a series of articles in JACS
between 1914 and 1920 on ocalyl chloride and bromide. The reaction of oxalyl chloride with carboxylic acid to give acyl chloride or anhydride
depending on molar ratio of reactants is a general one. It is most efficient with aryl carboxylix acids. With lower aliphatic acids is work better on
the sodium salt. I posted the articles long ago. UTFSE or go to the ACS search engine.
Tarbutton also in JACS in 1940 and no you will not find more details elsewhere. The reaction between P2O5 and NaCl or CaCl2 works, and is probably
the best way to make POCl3 and possibly PCl3 that does not involve elemental P or preformed PCl5.
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benzylchloride1
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Success with acetic anhydride synthesis:
I tried one of the rodium procedures today and I got some acetic anhydride. 3.5 g of sulfur powder was dissolved in 20 mL of bromine prepared from
sodium bromide sulfuric acid and 35% hydrogen peroxide and dried with sulfuric acid. 66.5 g of commercial anhydrous sodium acetate was added to a 500
mL round bottomed flask. A pressure equalizing addition funnel was attached to the flask. The sulfur bromide was poured into the funnel. The sulfur
bromide was added to the mixture in small portions. A reaction ensued and orange colored liquid refluxed. After the addition, the mixture was stirred
with a glass stirring rod until the mixture has turned to a white solid in a clear liquid. A distillation apparatus was assembled and the mixture was
distilled, collecting the fraction between 120 C -125 C @ 580 mm Hg. A clear irritating smelling liquid was obtained. Around 16 g was obtained. Much
acetic anhydride remained in the flask, the distillation was stopped because of charring in the bottom of the flask. O-toluidine was dissolved in
dilute HCl. 0.5ml of the acetic anhydride was added along with 1 g of sodium acetate, the mixture was stirred and a oil formed. The mixture was poured
into cold water and lumps of o-acetyltoluidine formed. The o-acetyltoluidine was dissolved in boiling water, filtered and cooled. Needles of the
product formed. A melting point will be taken once the derivative is isolated. This procedure indeed works; I will try it again on a larger scale. The
acetic anhydride produced smelled like the acetic anhydride I used at the university. I will take my product to the university and get an IR spectrum.
I wish I had my IR spectrophotometer running. I plan on trying the S2Cl2 method in a few weeks.
Amateur NMR spectroscopist
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chemrox
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JACS paper on acid anhydrides
Wallace and Copenhaver, March 1941, JACS, Anhydrides of the Normal Aliphatic Saturated Monobasic Acids.
In the paper the following is stated:
In general the method of Holde and Tacke was used.
The acids were refluxed for six to eight hours in a flask, with
ground-in condenser, with three equivalents of acetic
anhydride. The acetic acid and excess acetic anhydride
were distilled off under vacuum and the resulting anhydrides
purified by vacuum distillation or by recrystallization
from a suitable solvent. The anhydrides from heptylic
through pelargonic were distilled under vacuum and
capric through stearic were recrystallized three or four
times from either diethyl or petroleum ether by cooling in
an ice-salt-bath or with dry-ice. The yields ranged
from 50 to 80%.
The question is, what is unique about acetic anhydride in facilitating the dehydration of other monobasic acids? What is the mechanism? Is there
another anhydride, say with a much higher boiling/melting point that would accomplish the same thing?
Attachment: JACS Wallace & Copenhaver 1941 anhydrides.pdf (218kB)
This file has been downloaded 1258 times
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Sauron
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Ac2O was and for some still is cheap and ubiquitous,
Vogel also describes this reaction.
I doubt that you need reminding that anhydrides are available from their acyl chlorides snd the acids, or sodium salts of the carboxylic acids. or the
acids or salts with oxalyl chloride.
See the Fresh Look thread I started some time back, as benzylchloride had the good sense to bypass the irksome double fusion of sodium acetate
trihydrate which several members got all vexed about. He did what I recommended way back and simply purchased anhydrous NaOAc and he SUCCEEDED in
making Ac2O from either preformed S2Cl2, or from S and Br2. In fact he did not even gibe his NaOAc a simple single fusion, he used it out of the
bottle. (Not recommended.) And he needed a little nudge about vacuum to get his yields up but that has been accomplished.
So follow his lead and you can have all the Ac2O you need and therefore all the other anhydrides through it.
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SYDN
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Engager, could you to downloud video again please
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hector2000
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Another way for making Ac2o is carbonylation of methyl acetate
Accoding to patent number 4556519 we should use Nickel powder, Methyl iodide, Stannous acetate and Lithium acetate as catalyst and we should use 80
bar pressure
80 bar pressure is not huge pressure for example oxygen capsule has 150-180bar(~atm) pressure.
Usng these catalyst is necessary?
This is possible to use just Acetic acid,Methyl acetate+CO with 80-100 bar pressure?
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JohnWW
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Quote: Originally posted by hector2000  | Another way for making Ac2o is carbonylation of methyl acetate
Accoding to patent number 4556519 we should use Nickel powder, Methyl iodide, Stannous acetate and Lithium acetate as catalyst and we should use 80
bar pressure
80 bar pressure is not huge pressure for example oxygen capsule has 150-180bar(~atm) pressure.
Usng these catalyst is necessary?
This is possible to use just Acetic acid,Methyl acetate+CO with 80-100 bar pressure? |
http://www.freepatentsonline.com/4556519.pdf
(Need to log in first)
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not_important
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http://www.pat2pdf.org/
No login needed.
In answer to hector's question, there are a number of articles in the journals on this general reaction and a search will quickly direct you to some
of them. The short summary is "yes, the catalysts are needed, for a variety of reasons."
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unome2
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Sauron, I don't recall the article by Tarbutton, et al, requiring a pressure vessel... The reaction between P2O5 and NaCl does, according to that
paper, commence @ around 250C:
| Quote: | The Reaction of Phosphorus Pentoxide with Metal Chlorides.*-The reaction of phosphorus pentoxide with calcium chloride and with
sodium chloride in an iron or stainless steel vessel produced a mixture of phosphoryl trichloride, phosphorus trichloride and hydrogen chloride. The
weight of the first compound was from three to ten times that of the second and the weight of hydrogen chloride formed was proportional to the water
in the charge. The phosphorus trichloride could have resulted from the reduction of phosphoryl trichloride by the metal reaction vessel. A trace of
elemental chlorine was detected among the volatile products, but no phosphorus pentachloride was obtained. The reaction between phosphorus pentoxide
and sodium chloride began at about 250C and the analogous reaction between phosphorus pentoxide and calcium chloride at about 400 C.
* Taken from Tarbutton, et al, 'Phosphorus Halogen Compounds from Phosphorus Pentoxide and Halides: Properties of Phosphorus Trifluoride and
Phosphorus Oxyfluoride' (1941) 63(7) JACS 1782, 1785} |
There would appear to be NO need for a pressure vessel, merely condense the product of the destructive distillation (although a steel vessel probably
would be sane). Nonetheless, by using a basic design - solvent can and steel condenser - it should be thereotically possible to produce enough POCl3
to make a serious quantity of Acetic anhydride at home.
In fact, this could be remarkably OTC IF we can work out a decent route to P2O5 @ home... I wasn't answered before, but would a lime-kiln (propane
flame) design with a fine spray of phosphoric acid coming in from the top work? (ie. spray drying the acid - H3PO4 - to the anhydride - P2O5)
As to the production of SO2Cl2 you cited before using Camphor/Activated charcoal, here's a present
Attachment: SO2Cl2.InorganicPreparations.Henderson.Fernelius.140.3.pdf (92kB)
This file has been downloaded 1079 times
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pHzero
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How about heating zinc acetate in a vacuum? Wiki says that makes acetic anhydride. http://en.wikipedia.org/wiki/Zinc_acetate
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hissingnoise
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It's certainly tantalising at first glance---but vacuum may mean vacuum in this case rather than reduced pressure. . .
Some investigation would seem to be in order, anyway.
If it worked at all that salt will be popular!
On second thoughts, it's way too good to be true. . .
[Edited on 8-6-2009 by hissingnoise]
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497
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I think it's true. According to the attached paper 250*C at 0.2mm for 6 hours does the trick. The yields of the "basic acetate" are around 50%, so I
would imagine the yields of acetic anhydride would be similar, although they did not say.
They give the equation:
4(RCO2)2Zn --> (RCO2)6Zn4 + (RCO)2O
I wonder if a 0.2mm vacuum is necessary for yielding acetic anhydride. It may be that the acetic anhydride and basic zinc acetate are formed at lower
vacuums, but the acetate decomposes making it useless to prepare the acetate (which is all the researchers are intersted in)
Unfortunately, it would probably take over 1000g of zinc acetate to yield 100g acetic anhydride..
Attachment: BasicZincAcetate.pdf (250kB)
This file has been downloaded 2608 times
[Edited on 8-6-2009 by 497]
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hissingnoise
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Thanks for that 497, it's interesting but for me pyrolysis of acetone still seems to be the least unattractive method so far. . .
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pHzero
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I just heated some dry ASA (acetylsalicylic acid, aka aspirin) with a tiny bit of water and it smelt strongly of vinegar. I'm guessing that smell came
from acetic anhydride since i only added a tiny bit of water.
This formula seemss to suggest so (note only 1 mole of water for every 2 moles of aspirin):
2C6H4COOHOAc (aspirin) + H2O --> 2C6H5COOH (salicylic acid) + Ac2O
Whereas with an excess of water, presumably you'd make acetic acid:
C6H4COOHOAc (aspirin) + H2O --> C6H5COOH (salicylic acid) + AcOH
I used up all my aspirin trying that though, but I'm going to head off to the supermarket to get something to eat, so i'll get another 32 tablets
(9.6g of ASA) while i'm there, then I might try it again with a proper still setup to condense the vinegary vapours
[Edited on 16-6-2009 by pHzero]
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