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Author: Subject: Acetic anhydride preparation
Drunkguy
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[*] posted on 15-11-2006 at 03:54


The article in the quotation is for the Dreyfus procedure. I too liked the look of this but I would think you want to not add the carb. acid through an addition funnel. Rather have a 2 stage set-up:

Sodium metaphosphate at 150C in a rbf with a still-head and condenser attached. Then i'd want to pass the carb. acid vapors into this via a second rbf that is boiling the acid. That way the mixture stays 'moist' or 'saturated' but does not get drenched.

Sodium metaphosphate is readily available btw.

Edit: Actually that idea is quite foolish since the acid vapors would condense en route to the reaction vessel.

There's got to be a better way though such as packing a column with the metaphosphate and condensing the vapors afterwards [but then the column would not be 150C though]

A mechanical stirrer might be a good idea.

Then ultra-sonification tends to help promote various reactions, I like this idea.

[Edited on 15-11-2006 by Drunkguy]
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[*] posted on 30-11-2006 at 09:56


Anybody know if this reaction is feasible:

S2Cl2 + 2RCO2H -> 2RCOCl + SO2 + H2S

If one has really good clean triple distilled sulfur monochloride I see no reason why the product would need to be distilled since the by-products are all gases. Ofcourse its always a good idea to distill it anyway.

Im only interested in the monochloride btw and not SCl2. Partly because the equations are harder to balance, but mainly because SCl2 is scarcer.


[Edited on 30-11-2006 by Drunkguy]
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[*] posted on 30-11-2006 at 13:41


With S2Cl2 you don't use GAA (the gases evolved will carry away the volatile acetyl chloride), you use an excess of anhydrous sodium acetate. This way, acetic anhydride is directly formed. The procedure is on rhodium and is possibly the easiest method to make acetic anhydride.



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Drunkguy
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[*] posted on 30-11-2006 at 14:40


On wiki though this reaction is possible where they use thionyl chloride although the by-products are gases:

H3C-COO-H + O=SCl2 → H3C-COCl + SO2 + H-Cl

The NaO2CR method is all well and good if you want the anhydride, but supposing somebody wants the chloride. Plus since the boiling point of S2Cl2 is >100C surely the more you heat the mixture on distillnig it the greater the chance of carrying over sulfur rubbish into the receiver?
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[*] posted on 7-12-2006 at 11:28


Hi all

Just dabbling here but what would happen if you reacted peroxyacetic acid and acetaldehyde under presure (to reduce CO2 and Methane production ie if this reaction had to happen at all) Water produced would also have to be removed.

[Edited on 7-12-2006 by freachem]
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[*] posted on 7-12-2006 at 22:35


Momentary laps in concentration, I figure more acetic acid will form.
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[*] posted on 22-12-2006 at 22:50


1. There's an old Russian process from the 40s. Anhydrous sodium acetate (freshly fused and ground) is mixed with sulfuryl bride which itself is made in situ from Br2 and sulfur (maybe I should copy this to the What Can I do with Sulfur? thread.) The mixture is stirred then rotavaped at reduced pressure, the Ac2O is redistilled fractionally at ordinary pressure. The detailed procedure is available online (Rhodium) The snag is that you need liquid bromine.

2. It is well known that Ac2) can be made from acetyl chloride. The problem is that most places where Ac1O is verboten, so is acetyl chloride. Fortunately acetyl chloride is easy to make IF you can get cyanuric chloride (which is cheap) or Oxalyl chloride (which not cheap.) Cyanuric chloride ("CC") is mixed dry with anhydrous sodium acetate and dry-distilled. I believe it is 8 hours at 100C IIRC. Or, simply mix CC with a large excess of acetic acid (glacial of course) and heart to reflux, until no more cyanuric acid precipitates out. That was proposed as a prep method for cyanuric acid a long time ago (c.100 years). Both AcOH and CC are cheap. Acetyl chloride is the side product. Note that 1 mol CC chlorinated three mols AcOH. You must fractionate the Acetyl Chloride from the excess AcOH Then use it to make Ac2O.

A more contemporary procedure uses CC in soln on acetone to chlorinate acetic acid at RT in presence of TEA. Only one Cl on the CC is involved, the hydroxy-CC precipitates out. The yield is about 50% and one is left to work up the acetyl chloride from the TEA and acetone. I'd guess, bubble in some HCl gas, filter off the TEA-hydrochloride solid, then remove the acetone on a rotovap, or fractionate, there's a decent difference in b.p. between acetone and acetyl chloride.

The other procedures are more attractive on a larger scale. The third procedure is good for making acetyl chloride to react in situ to produce an amide or ester for characterization purposes. This procedure was from Tet.Lett and I believe used to be up on the defunct old Hive (pre-Rhodium) board.

Roger Adams in JACS c.1916-1920 wrote up general procedures for making acid anhydrides and alkyl chlorides from the corresponding acids with oxalyl chloride. This is very efficient but costlier than the CC methods because of the molar ratios and the cost of the oxalyl chloride.

I hope this is helpful.
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[*] posted on 28-12-2006 at 14:01


Here's the article citation for the TCT prep of acetyl chloride from acetic acid in 87% yield, at room temp, 3 hours stirring.

Tetrahedron Letters 40, 4395 (1999)

Same procedure, oxalic acid (anhydrous) to oxalyl chloride 52%

So you can make acetyl chloride and use it to make acetic anhydride by well known methods. (like reacting with anhydrous sodium acetate.)

Or you can make oxalyl chloride and use it to make acetic anhydride directly from acetic acid - the acetyl chloride is formed first then reacts with more oxalyl chloride to give the anhydride.

Best route that I know of.
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[*] posted on 29-12-2006 at 07:48


Here's the Merck tech data sheet on CC which used to be on their site, they no longer give these away online. There are a number of citations of interest including the one above.

Also the Acros tech data sheet (current) with prices. More citations.

And the Aldrich tech bulletin on oxalyl chloride illustrating numerous reactions and with citations to the literature.

Hope these are useful to some of you.

[Edited on 29-12-2006 by Sauron]

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[*] posted on 18-1-2007 at 09:43
acetic anhydride peparation


set up appartus for adding and distilling with a gas capture tube (inverted funnel over water) (hood!)

27 g glacial acetic in the flask; 23 g PCl3 in an addition funnel
keep reaction mixture cool while adding PCl3 slowly
after standing for about 10 min heat gently distilling acetyl chloride as the product add two drops of glacial acetic to product get rid of any PCL3.

Same setup as above, put 30 g of ahydrous NaAc in the flask add 18 ml acetyl chloride in the addition funnel. Add AcCl dropwise to the cooled flask (ice bath). After addition is complete, remove ice bath and heat until no more distillate comes over. Add 2-3 g finely powdered NaAc to the distillate.

yield should be 15-20 g

obviously this can be ramped up as needed.

Notes: NaAc has some water. Fuse in a porcelain dish until no more vapor evolves but avoid overheating


Source: Adams, Johnson & Wilcox, 1963, Lab Exp Org Chem, 5th edition, Macmillan Co.

[Edited on 18-1-2007 by chemrox]
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[*] posted on 18-1-2007 at 17:05


Cool if and only if you have an abundant cheap source r PCl3 which most everywhere due to Chem Warfare Convention is no longer the case.

Therefore, you must make Acetyl Chloride another way.

See posts above. You can make acetyl chloride (1) from AcOH and CC or (2) you can make either acetyl chloride or Ac2O directly from AcOH and uxalyl chloride.

First reagent is far cheaper, second is more convenient.

Oxalyl chloride you can make from oxalic acid and CC or anhydrous sodium oxalate and CC. CC = cyanuric chloride.

You can buy CC and/or oxalyl chloride in most places without any special restrictions.

Use of a hood is STRONGLY advised.
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[*] posted on 19-1-2007 at 16:05


Why use PCl3 if SOCl2 can get the job done?



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[*] posted on 19-1-2007 at 22:41


In many places SOCl2 is now simply unavailable.

In Thailand it is flatly prohibited. See Merck Thailand website where they flatly state WE DO NOT IMPORT THIONYL CHLORIDE.

Although possible to make, it is hardly worth the bother when other routes to acid chlorides are at hand. The main utility of SOCl2 is that the byproducts of chlorinating an acid are both gases and this simplifies workup. The same is true of oxalyl chloride. Gases only (CO and CO2).

The most convenient way to make SOCl2 is to pass a mixture of PCl3 and SO2Cl2 through activated carbon under specific conditions. This mixtures disproportionates to POCl3 and SOCl2, which can be fractionated. As SO2Cl2 is readily made by reacting SO2 and Cl2 gases over AC or camphor, effectively this is a facile route to both SOCl2 and POCl3 both of which are useful and now politically incorrect.

The only tricky part is obtaining the required PCl3.

A recent improvement in the catalyst which extends the life of the bed, has the CWC people rather upset.

The prior method of making SOCl2 was oxidation of SCl2, S2Cl2 or a mixture of the two with SO3, or high % oleum, in a pressure reactor, while introducing Cl2 to control side reactions. This would not be such a simple lab scale prep. The sulfur chlorides are available by direct rxn of the elements or more usually on industrial scale as byproduct of manufacture of CCl4 via chlorination of CS2. Again over AC.

The intermediate formed, trichloromethyl sulfenyl chloride, or perchloromethyl mercaptan, is a taxic compound. It is quantitatively reduced by iron filings to CCl4. This is whi CCL4 plants are usually sited alongside CS2 plants.

The perchloromethyl mercaptan can be utilized differently, to produce thiophosgene instead, which is useful in medicinal chemistry. The old method using SnCl2 sucks, and has been supplanted by a catalytic bed to silica gel at about 140 C. By products are molten sulfur and a whole lot of hot angry H2S. The thiophosgene, a toxic liquid, is condensed out by a series of condensers and the H2S ends up in a large caustic scrubber. I believe Akso holds the patents.
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[*] posted on 27-1-2007 at 02:32


Could someone clear up for me what the distilation of heating dry asprin is. The asprin turns into a brown liquid that hardens after cooling and a clear strongly acetic smelling liquid that doesn't freeze in a home freezer distills off.
Thank you.
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[*] posted on 27-1-2007 at 04:49


@CD-ROM LAUFWERK, how did you distill your product? Did you fractionate it?

You haven't reported the bp. That would tell the tale.

The bp of acetic anhydride is quite different from that of acetic acid.

Also if your reaction went as you say you would have some phsphoric acid left in the pot. It is very high boiling.

Acetic anhydride is flammable, acetic acid is not. Try igniting a small sample.
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[*] posted on 16-2-2007 at 09:47


Most interesting.... Methyl Acetate can be converted into acetic anhydride via....

Carbonylation of Methyl Acetate to Acetic Anhydride
The reaction conditions used were similar to those reported for the Eastman Chemical acetic
anhydride process. Into a 300-cc autoclave were added [Rh(dppe)2]+ Cl- (0.46 g), MeOAc (0.695
mol), CH3CHI (0.074 mol), and HOAc (0.29 mol). The contents were pressurized with a 95/5
CO/H2 mix, reacted at 190°C and 750 psi for 4 hours and then analyzed by gas chromatography.
The results are compared with other catalytic runs in Table 3.2.1.
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[*] posted on 7-3-2007 at 04:33


Someone else looked into the reaction of silver acetate with CS2, but gave a yield figure this time, 45%. Looks like those dudes in 1865 had their shit together, and were smart enough to try the slightly less expensive Pb acetate, too.

From Proc. Chem. Soc. 20, 1957.

A New Synthesis of Carboxylic Acid Anhydrides
By D. Bryce-Smith
(Chemistry Department, The University, Reading, Berks.)

Reactions between silver carboxylates and carbon disulphide appear not to have been described in the literature. Very little reaction occurs when a silver carboxylate, e.g., silver benzoate, is heated under prolonged reflux (46°) with carbon disulphide; but it has been found that at 100—150° reaction is complete within 6—20 hours. The acid anhydride is produced. The overall equation may be written as follows: 2RCO2Ag + CS2 -» (RCO)2O + CO2 + Ag2S. The pure anhydride has been obtained in yields of 98.0, 98.5, 100, and 45% with R = Ph, m-NO2C6H4, p-BrC6H4, and Me, respectively. These reactions are very clean, and the only other organic product in each case has been the free carboxylic acid, probably produced by fortuitous hydrolysis. Since silver carboxylates can be made almost quantitatively from the free adds, the method makes possible a virtually quantitative conversion of acids into anhydrides under neutral conditions. Sodium salts appear to be unsuitable for this reaction.

The following preparation illustrates the method. Silver benzoate (2.90 g.) was heated with dry carbon disulphide (8 ml.) in a sealed tube at 100° for 8 hr. After cooling in solid carbon dioxide-alcohol, the tube was opened. On warming, carbon dioxide (0.18 g.) was evolved. The tube was washed out with dry ether, and the washings were evaporated to give pure benzoic anhydride (1.40 g., 98%), m.p. and mixed m.p. 42—43° without recrystallisation.

It is suggested that the reaction steps in the annexed scheme are involved. This is supported by the observation that carbon tetrahalides also react with silver benzoate, to give benzoic anhydride.
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[*] posted on 7-3-2007 at 13:05


I think that the pyrolysis of silver acetate would be a way more attractive route for most members here, which are not able to prepare CS2.
As the pyrolysis of silver acetate yields oxygen besides acetic anhydride, there will also be no need for inert atmosphere.
I think the admin of the german forum got this info from Gmelin, the giant german inorganic chemistry lexicon.




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[*] posted on 7-3-2007 at 16:51


That's a rather pricey route to Ac2O. Check out the yield per Kg of silver acetate and then go price the silver acetate..

I suppose you can obtain silver metal on the spot market and make your own acetate, the prep doesn't require AR grade. That will get you "some" economy. But the overwhelming % Ag by weight in silver acetate makes this unfavorable.

But I don't see this route being economically competitive with other routes that are available even to chemically challenged EU residents. Setting aside TCT and oxalyl chloride, you ca make acetyl chloride from benzoyl chloride and then react the acetyl chloride with sodium acetate.
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[*] posted on 8-3-2007 at 00:30


Yeah, silver salts are notoriously unrecoverable and unreducable; and scrap silver has no resale value, certainly not twice as much as it cost as .999 bars 3 years ago. Might as well just pour it down the drain.

I'll take a look in Gmelin's unless someone beats me to it, but I suspect that the statement may deal with this JACS article. Or maybe it's from an article where a 4% yield was obtained under high vacuum, in combination with some exotic catalyst; which is what these quotes always fail to mention. I have a feeling that putting a pile of silver acetate in a flask and distilling will not go well, but who knows.

Edit: Not only is Ag, Pb, Al, Fe etc. acetate heating on the record as possible in some way, mostly impossible as tried, or vaguely possible; the patent numbers have been given, and the journal references have been given. Look them up, present them, translate them, do them, tell us how it goes, or just keep blah blah blah blah blah blah blah blah blah blah blah blah blah. Whatever you do, don't stop blah blah blah blah blah blah blah.

[Edited on 8-3-2007 by S.C. Wack]

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Sauron
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[*] posted on 8-3-2007 at 01:07


I used to casually know some people who recovered Ag from photographic emulsions and solutions, mostly from labs that processed medical radiographs (maybe industrial ones too.) I did not pay much attention to their technology.

I did by a large PE tabletop Buchner funnel from them about two feet across and maybe 10" deep (to the frit). Still have it.

Silver cyanide used to be standard for making isonitriles but has been superceded by better methods. Likewise silver fluoride is mostly obsolete for fluorination reactions. And last month when I priced some silver nitrite the price scared me out of that procedure. I have a few hundred g of silver nitrate around here, which I guess I will hoard. Ag salts are to be worked with with OPM (Other People's Money.)
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[*] posted on 8-3-2007 at 01:23


It has been reported that distilling hydrated cupric acetate gives acetic acid and a small percentage of the anhydride with a residue of CuO ( Bamdas & Shemyakin, Zhur. Obshchei Khim. 18, 324-326 1948)

It might prove interesting to try this with the anhydrous acetate. If decent yields of Ac2O were obtained it could be a useful small scale route

CuO + 2 AcOH => Cu(OAc)2 . H2O (OK, actually Cu2(AcO)4 . 2 H2O )

Cu(AcO)2 . H2O ==(100 C, vac)==> Cu(AcO)2 + H2O (g)

Cu(AcO)2 ==(heat)==> CuO + Ac2O

but right now I'm attempting to repair a malfunctioning room heater.
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[*] posted on 8-3-2007 at 01:41


If you are going to try the copper acetate route, I suggest that you precipitate a Cu(II) salt with an alkali carbonate or an alkali hydroxide. I recommend the first because any significant sized version of the second reaction is exothermic enough to decompose the Cu(OH)2 on the spot to CuO. The (basic) copper carbonate you obtain this way settles out of the reaction mix more nicely than the cupric hydroxide. Either of these dissolve very readily into acetic acid forming a characteristically blue solution (I have a water bottle full of it made with 5% vinegar sitting in front of me now). From personal experience, the extremely weak nature of acetic acid makes the reaction with CuO mind numbingly slow. Some granules I had thrown in vinegar once took several days to dissolve, whereas the basic carbonate will finish up in a few minutes. Just my two cents here. If I had vacuum to dehydrate the acetate, since it is simple enough to make, I would definetly give it a shot.
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[*] posted on 8-3-2007 at 02:13


Destructively distilling copper acetate is likely a good way to make AcOH with a trace of anhydride. But there's no shortage of AcOH is there?

I understand TCT is hard to buy in Germany or all of Europe. Oxalyl chloride is a little pricey, and for all I know may also be regarded as toxic (perhaps with better justification than in case of TCT.) But, what about benzoyl chloride?

Because that's a prep that can be run on a decent scale, the reagent is cheap, and it works well. The report on this in JACS was by Herbert C.Brown, in his youth. H.C. Brown would later achieve fame worldwide as "Boron" Brown and I doubt there's an organiker anywhere who does not know his story.
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[*] posted on 8-3-2007 at 02:59


Ah, but while distillation of hydrated cupric acetate gives mostly acetic acid, I was speculating on the extension of this to the anhydrous acetate, for which I am unable to prepare a balanced equation that leads to acetic acid.

I would not fell at easy purchasing benzoyl chloride, and have lived in areas where I could not purchase it.
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