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Author: Subject: Acetic anhydride preparation
LSD25
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[*] posted on 14-6-2008 at 19:56


Well it depends upon whether the reaction could be undertaken below the boiling point of MsCl doesn't it?

In that respect, this article might be of some, slight interest:

Quote:
J. Org. Chem., 62 (11), 3552 -3561 jo960441u S0022-3263(96)00441-0
Copyright © 1997 by the American Chemical Society

DOI: 10.1021/jo960441u

Mechanism of Polyphosphoric Acid and Phosphorus Pentoxide-Methanesulfonic Acid as Synthetic Reagents for Benzoxazole Formation

Ying-Hung So* and Jerry P. Heeschen

Central Research & Development, 1712 Building, The Dow Chemical Company, Midland, Michigan 48674

Received: March 4, 1996

Abstract:

The mechanism of 2-phenylbenzoxazole formation from benzoic acid and o-aminophenol in polyphosphoric acid (PPA) is studied by NMR spectroscopy and chemical analysis. Benzoic acid reacts with PPA to form benzoic-phosphoric anhydride and benzoic-polyphosphoric anhydride. The ratio of mixed anhydride to free carboxylic acid increases dramatically as the P2O5 content of PPA increases, but this ratio is independent of reaction temperature and time. When o-aminophenol dissolves in PPA, part of the hydroxyl group is converted to phosphate ester, and only protonated amine is detected. Benzoic acid, mixed anhydride, and PPA are in dynamic equilibrium, and so are PPA, o-aminophenol, and its phosphate ester. The mixed anhydride and o-aminophenol react to form 2-aminophenyl benzoate as the first reaction intermediate which undergoes rapid acyl migration to generate 2-hydroxybenzanilide. Ring closure of 2-hydroxybenzanilide to form 2-phenylbenzoxazole is acid catalyzed. The reactive components in phosphorus pentoxide-methanesulfonic acid (P2O5-MSA) which is a convenient alternative to PPA are very similar to those present in PPA. Benzoic acid is also converted into mixed anhydride in P2O5-MSA.


Seems to me that if the benzoic acid forms a mixed anhydride, that addition of the sodium benzoate (or sodium carbonate) should be sufficient to give the benzoic anhydride, which gives access to a classic route to many aliphatic anhydrides. Alternatively, it would be very interesting to see if the acetic/propionic anhydrides could be formed in-situ when reacted with the P2O5-MSA mixed anhydride, wouldn't it?




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[*] posted on 14-6-2008 at 20:52


Far, far easier and simpler and more promising to replicate the tosyl chloride method - which you get the credit for digging up, not me.

Mesyl chloride seems like a lot more trouble.

Its sole virtue being that DMSO is cheap. I would argue that anyone who can get DMSO can get tosyl (p-toluenesulfonyl) chloride.

If the object of the exercise is to have fun exploring the MsCl prep and route to acetic anhydride, then by all means, enjoy yourself.

I rather thought the point was pretty much to get to Ac2O by the most accessible and convenient means possible.

Dry NaOAc + TsCl sans solvent looks like that to me.

Cheaper than the oxalyl chloride route

Simpler than NaOAc + S + Br2 (or a preformed sulfur halide)

Simpler than the fiddly and hazardous ketene process.

Does not require AcCl (maybe it forms that in situ?)

You really can't get much simpler than a melt of two solids to make a liquid than promptly boils off to be condensed. No solvent, one pot, isolation accomplished. TsCl is not a suspicious chemical at all. Neither is sodium acetate.

All that is left is to actually try it.

As to NaOAc, I have a Kg of commercial anhydrous Merck, never opened. I also have a thermostated forced air drying oven that goes to 250 C and a 12" evaporating dish. The oven is by Memmert. I bought it new.




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[*] posted on 14-6-2008 at 22:22


Yeah, I do like the look of the TsCl route - it has some serious benefits - but although I can get DMSO, but not TsCl (I could make it, but that ain't trivial) it probably is beyond my means.

The use of simple polyphosphoric acid (once again, monoammonium phosphate + heat = polyphosphoric acid + ammonia) and benzoic acid to form the mixed PPA-Benzoic anhydride should, maybe with additional sodium benzoate, give the benzoic anhydride which would be simpler than even the MsCl route - especially given that benzoate salts and the monoammonium phosphate (the fertilizer grade variety is coated with an organic grease and contains about 50% inert, insoluble material, the bit you want is highly soluble in water) are cheap and easily sourced.

What would be interesting is to try the PPA/phosphoric anhydride route to AA through GAA & NaOAc, that would truly be cheap, simple and scaleable.

But if one added benzoic anhydride to GAA, surely there would be AA produced (the converse of adding AA to benzoic acid to produce benzoic anhydride: http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...)

PS For those who have p-toluenesulfonic acid or who are using there TsCl and don't want to buy more in order to do it again, the attached material might be of interest

{EDIT}

Bloody thing didn't attach, here goes again

[Edited on 14-6-2008 by LSD25]

Attachment: TsOHtoTsBr.pdf (80kB)
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[*] posted on 15-6-2008 at 00:00


If one has access to bromine then the Russian method (in situ generation of sulfur bromide and reaction with anhydr NaOAc) opens up. The intermediate decomposes on mild heating to Ac2O.

This is fully described upthread.

Benzoic anhydride is commercially available is it not? Simple enough therefore to see if the reactions you propose have merit.

Len 1 has spent a lot of time and effort demonstrating how SO3 can be made, so has garage chemist. If you have SO3 or oleum (fuming H2SO4) and can generate dry HCl you have the means to make chlorosulfonic acid. If you have chlorosulfonic acid and toluene you have all you need to prepare TsCl. I think it is more trouble than $45 a Kg is worth, but that's just me. I don't know of any simple way to chlorinate TsOH to TsCl. AFAIK the chloride is always prepared from toluene and chlorosulfonic acid.




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[*] posted on 15-6-2008 at 17:51


I am having problems constructing an equation or equations for the reaction of p-toluenesulfonyl chloride and anhydr. sodium acetate to form acetic anhydride.

This reaction is reported in JACS as proceeding in high yield (90%) with equimolar amounts of reactants on a 22 mmol scale, without solvent, and with heating to 180-200 C for 30 minutes.

The TsCl will be liquid at such temp. Sodium acetate will presumably dissolve or be suspended in the melt; anhydrous NaOAc decomposes at >300 C, but this is well above the reaction temperature. TsCl boils at 324 C/10 mm Hg, so again the reaction temperature suggests no obvious decomposition.

I would prefer to understand the reaction better before trying it. Is HCl produced? What is left in the pot? I would guess, NaCl and p-toluenesulfonic acid (TsOH) but initial attempts to write an equation along the lines of

2 TsCl + 2 NaOAc -> (MeCO)O + 2 TsOH + 2 NaCl

fail to balance.

Sodium tosylate is a possible product. But that leaves us with chlorine. Is the tosyl chloride merely catalytic? If so what happens to the sodium?

Does a mixed anhydride of p-toluenesulfonic acid and acetic acid form as an intermediate?

I don't recall ever hearing of anhydrides of arylsulfonic acids..

At the moment I am suffering from Chemrox Syndrome, a severe head cold, and cannot think.

HELP!

[Edited on 16-6-2008 by Sauron]




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[*] posted on 15-6-2008 at 18:18


Aliced25, that article sued toluenesulfinic to form the tosyl bromide, not the sulfonate unfortuanly.

EDIT: apparently, a mixed anhydride is forme din this reaction, not the acyl chloride:

Quote:

Synthesis 2004: 205-207
DOI: 10.1055/s-2003-44381


A Cheap, Simple and Efficient Method for the Preparation of Symmetrical Carboxylic Acid Anhydrides

Foad Kazemia, Hashem Sharghi*b, Mohammad Ali Nasserib
a Department of Chemistry, College of Sciences, Chamran University, Ahvaz, I. R. Iran
b Department of Chemistry, College of Sciences, Shiraz University, Shiraz, 71454, I. R. Iran
Fax: +98(711)2286008; Email: shashem@chem.susc.ac.ir;
Received 13 October 2003
Abstract

A manipulatively simple and facile one-pot procedure for the synthesis of symmetrical anhydride is reported. Treatment of carboxylic acids with tosyl chloride in K2CO3 media under solvent free conditions gives the corresponding anhydrides in good to excellent yields in a short reaction time via carboxylic sulfonic anhydride as the key intermediate.


Howeevr, I have seen several procedure using TsCl to form acyl chlorides, so I was pretty sure the reaction goes through acetyl chloride.

TsCl can be produced from TsOh by reacting with chlorosulfonic acid, which is pretty irrevelant here. Chlorination of TsOH leads to ring-chlorinated products (US 4131619)


Found this:

US patent 4696774

Quote:


In Yet another method, arylsulfonic acid is reacted with a sulfur monohalide in the presence of excess halogen. This latter method is especially useful in the production of benzenesulfonyl chloride wherein benzenesulfonic acid, sulfur monochloride and chlorine are reacted to produce benzenesulfonyl chloride. In this process described immediately above, the arylsulfonyl halides produced can be removed by distillation from the reaction mixture.
However, the distilled arylsulfonyl halide product is usually discolored by the presence of impurities and can be almost black in color. It would be advantageous from a customer's viewpoint to treat the arylsulfonyl halide with various decolorizing agents to achieve a pale yellow to colorless product of higher purity.



EXAMPLES

This experiment illustrates an improved process for producing
benzenesulfonyl chloride that can be decolorized by the process of this
invention.


To a 1 liter flask was added 808 grams (5.1 moles) of benzenesulfonic acid and 5.7 grams of a 70 percent solution of phosphorous acid (4.0 grams phosphorous acid/1.7 grams water). Sulfur monochloride addition was started and after all the sulfur monochloride had been added, chlorine was
bubbled into the reaction mixture for a period of 20 hours at 80°C. The resultant benzenesulfonyl chloride was removed by distillation.



This seems like themost convienient way of preparing sulfonyl chloride fromaromatic sulfonic acids. Aromatic sulfonyl chlorides cannot be prepared by chlorination of sulfur compounds such as thiosulfates, disulfides, thiols, etc.

The reaction could be done in one pot, preparing the S2Cl2 by chlorinating sulfur, adding the sulfonic acid once most of the sulfur has reacted, and continuing chlorination. The sulfonyl chloride can then be isolated and purified as mentionned in the patent.

Although this would be tedious just o obtain Ac2O (just aswell use S2Cl2 with AcONa!) It si a good way of obtaining aromati csulfonyl chlorides for other purposes, even though this is drifting off topic.

[Edited on 16-6-2008 by Klute]




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[*] posted on 15-6-2008 at 18:57


Carboxylic acid plus potassium carbonate will give the potassium carboxylate, and that reacts with the TsCl. I would not expect the carboxylic acid to have the pKa to dislodge TsOH from potassium tosylate if that formed first. Anyway thanks for the reference. I have Synthesis on CD so it won't take long to read.



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[*] posted on 15-6-2008 at 19:15


What I fail to understand, is how, by adding K2CO3 to an acid medium, and thus producing H2O, one can obtain an anhydride?! Why not use a preformed, dried potassium salt? I guess I need to read the protocole before guessing anything...



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[*] posted on 15-6-2008 at 19:36


Quote:
Originally posted by Sauron
I am having problems constructing an equation or equations for the reaction of p-toluenesulfonyl chloride and anhydr. sodium acetate to form acetic anhydride.


DE123052 equations. Add a CH3 as these are illustrated for benzenesulfonyl chloride, though only 1 of the 5 examples uses it, the others using p-toluenesulfonyl chloride.

Hadn't mentioned the patent before because if you can make or buy these chlorides, then you shouldn't have any problem making or buying acetyl chloride or acetic anhydride in the first place.

EDIT: If the pdf does not display in your browser, it is due to your Acrobat or browser settings. Use the "save full document" feature to save the patent.

[Edited on 15-6-2008 by S.C. Wack]
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[*] posted on 16-6-2008 at 02:40


Unfortunately the Iranian-authored paper from Synthesis (attached below) dies not apply to the lower aliphatic carboxylic acids, as the requirement is that the anhydride produced not be moisture sensitive.

That certainly does not apply to acetic anhydride.

In their procedure, the (solid) carboxylic acid and potassium carbonate are mixed in a mortar with grinding. TsCl moistoned with EtOAc is then added in small portions and the mixture ground for a specified period.

[Edited on 16-6-2008 by Sauron]

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[*] posted on 16-6-2008 at 08:59


The German patent cited by S.C.Wack does come to the point. It teaches that one equivalent of TsCl and anhydr NaOAc react to form AcCl and NaOTs, while one equivalent of TsCl and 2 equiv of NaOAc give one equivalent each of Ac2), NaOTs and NaCl.

It is well accepted that in the latter case AcCl forms first as per the first reaction, and then the AcCl reacts with the second equivalent of acetate salt to form the anhydride.

I am perfectly comfortable with this explanation. However, it forces me to go redo my calculations of the reaction from the JACS article I cited, which taught that equimolar amounts of TsCl and dry NaOAc (4.25 g and 1.62 g respectively, 22 mmol) gave 10 mmol Ac2O. rather than AcCl. (0.95 ml).

I rechecked my calculations.

The JACS article prepared sodium acetate from 3.7 g silver acetate, which is 22.2 mmol, so 1.82 g anhydrous sodium acetate. They heated this with 4.25 g TsCl, also 22.2 mmol.

Product 0.95 ml acetic anhydride, 10 mmol (about 1.06 g).

So my aithmetic is good, but we are left with this little anomaly.

Per the German patent why is this Ac2O and not AcCl?

[Edited on 17-6-2008 by Sauron]




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[*] posted on 16-6-2008 at 13:12


Well, i guess if you add another equivalent of AcONa, Ac2O will be formed?
In the preparation of AcCl, there is no excess acetate to react, while the patent yes? (I haven't read it, don't undersatnd german).




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[*] posted on 16-6-2008 at 17:57


Better to read it, or at least read the equations.

The same two steo process is also to be found in many other textx and publications and with a variety of chlorinating agents.

Step 1: the chlorinating agent (generally an acid chloride) reacts with the anhydrous NaOAc to form AcCl and the salt of the acid.

Step 2:

The AcCl reacts with more NaOAc to yield acetic anhydride.

This can be run as discrete steps with isolation of products.

The OVERALL reaction is (for tosyl chloride)

2 NaOAc + TsCl -> (AcO)2O + NaCl + NaOTs

If you go look at Roger Adams in JACS on oxalyl chloride as reagent for acyl chlorides and anhydrides you will see the same reactions and dtoichiometry, the major difference being that oaxalyl chloride falls apart to CO and CO2 and leaves less mess behind. Just NaCl.

I think I had better look at the Iranian paper again. I just did so and they employed 2 equivalents carboxylic acid to 1 of TsCl.
So the same stoichiometry prevails, the Iranians just propose a mixed anhydride mechanism in lieu of the classical one.

Anyway it is simple enough to try the JACS procedure both ways (with 1 equivalent, and with 2 equivalents.) If the first gives AcCl and the second Ac2O, fine. If both give Ac2O, also fine, from a preparative point of view.

In order to explain the result obtained in the JACS article, where equimolar amounts of TsCl and NaOAc are used, we would have to hypothesize that the formation of AcCl is slower than the reaction of AcCl with NaOAc to form the anhydride. Therefore only half the TsCl present reacts with NaOAc, because as soon as it does the AcCl formed consumes the remaining NaOAc to form Ac2O in the amount of half the equivalent of NaOAc present.

If the equimolar reaction produced Ac2O as reported and not AcCl, then half of the TsCl should remain unreacted in the post, while all NaOAc has been consumed leaving NaCl and NaOTs in equal amounts (roughly).

Since the authors are mum about such details we are left to try this experimentally.

Note the bp's. The reaction is run at 180-200 C. Ac2O boils at 140, acetyl chloride IIRC at 54 C. Therefore the reaction of acetyl chloride to form Ac2O MUST be instantaneous or AcCl will flash off at almost 3X its boiling point.

[Edited on 17-6-2008 by Sauron]




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[*] posted on 17-6-2008 at 18:58


Another possible, is far fetched explanation: human error.

In that JACS paper, which was after all not about this reaction but instead just using it in passing as part of an isotopic labelling procedure, the "acetic anhydride" produced, all 0.95 ml of it, was used directly in a Friedel Crafts acylation of benzene with AlCl3 to make acetophenone.

So it occurs to me that for their purpose acetyl chloride would have produced exactly the same result. So perhaps they simply misreported the intermediate as Ac2O when in fact it was AcCl.

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

It is noteworthy that the German patent teached running the reaction at the bp of Ac2O (140 C) and collecting the Ac2O at reduced pressure.

[Edited on 18-6-2008 by Sauron]




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[*] posted on 24-8-2008 at 17:56


I have fair ammount of thionyl chloride and sodium acetate, somebody has actual synthesis procedure for making Ac2O from this reagents?



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[*] posted on 24-8-2008 at 18:43


As Vogel's explains, thionyl chloride can't be used for preparing AcCl as the bp of AcCl and SOCl2 are too close to acheive a good seperation.

But, it could perhaps be possibly to react SOCL2 with 2-3eq of rigorously dried AcONa to form AcCl which reacts with more AcONa to form the anhydride, which could then be fractionnated from any unreacted SOCl2.

I'm not sure if the sodium salt will form the acyl chloride, or if the acid is needed. In that case, reacting AcOH and SOCl2 in a first step, then adding anhydrous AcONa, and fractionnating after some reflux could work. The thing is SOCl2 is usually used in excess, so if using stoechiometric amounts, you might have some unreacted SOCl2 in the soup.

It's hard to give a defiante answer. Try it out on a small scale?




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[*] posted on 24-8-2008 at 23:26


We have enumerated many ways in which NaOAc (anhydrous) can be used to prepare AcCl and/or Ac2O. I seriously doubt that SOCl2 is another one.

SOCl2 fails about as often as it succeeds.

As noted acetic through butyric acids are too close (as their acyl chlorides) to the bp of SOCl2 to seperate, cf. Vogel.

Trichloroacetic acid fails with SOCl2.

Oxalic acid (anhydrous) fails with 2 equ. SOCl2.

Malonic acid succeeds to extent of 60% yield.

Succinic and glutaric acids form only the cyclic anhydrides with SOCl2 not the acid dichlorides.

Same for phthalic acid.

So despite its vaunted reputation SOCl2 is a sometimes thing.

See attached study of the scope of reaction of thionyl chloride on a wide variety of carboxylic acids.

[Edited on 25-8-2008 by Sauron]

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[*] posted on 25-8-2008 at 05:35


Thanks for the reference but it is not what i'm looking for, i need detailed procedure on preparation of acetic anhydride from thionyl chloride and sodium acetate. In theory it seems easy:

2CH3COONa + SOCl2 => (CH3CO)2O + SO2 + 2NaCl

Any impurities such as acetyl chloride and unreacted SOCl2, should be easy to separate taking to account their low boiling ponts. However i'm looking for data about reaction conditions, and any problems that could be related with this synth. That's why i need exact synth procedure for this case.




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[*] posted on 25-8-2008 at 05:50


How can I or anyone else give you procedures for a hypothetical reaction that in my opinion will not work?

Sodium acetate (properly dried, not a trivial task) reacts with acetyl chloride to produce acetic anhydride.

Sulfur, bromine and anhydrous sodium acetate interact and on mild thermolysis release Ac2O.

Acetic acid or anhydrous sodium acetate react with oxalyl chloride to give acetyl chloride or acetic anhydride, depending on rations of reagents. Oxalyl chloride is expensive and the yields are not very good.

Acetic acid and cyanuric chloride react in acetone in presence of triethylamine to give acetyl chloride, which once isolated, reacts with anhydrous NaOAc to give Ac2O.

Ketene and acetic acid give acetic anhydride. Ketene is toxic (very).

If you have SOCl2, use it to make AcCl and react that with NaOAc anhydrous. Reacting SOCl2 with NaOAC is IMO a waste of reagents and time. SOCl2 only gives anhydrides of carboxylic acid in a few cases invariably involving dicarboxylic acids that can form a 5 or 6 membered cyclic anhydride. Acetic anhydride is not one of these.




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[*] posted on 25-8-2008 at 06:44


Quote:
Originally posted by Sauron
How can I or anyone else give you procedures for a hypothetical reaction that in my opinion will not work?


This reaction actualy work, and that is mentioned in patents and literature, for example russian chemical dictonary present reaction of thionylchloride with glacial acetic acid as one of methods for preparation of acetic anhydride (as well as SO2Cl2 and PCl3). So there is no question is it working - simply it is, but about exact reaction conditions.

[Edited on 25-8-2008 by Engager]




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[*] posted on 25-8-2008 at 07:49


Engager, acetic anhydride can be made by adding SOCl2 to boiling glacial acetic acid using a reflux condenser which is held at -15 to -20ºC, see: DE 396696, DE 411519. The yield was 81% with SOCl2 in example from the first patent, with pure chloride giving a much higher yield.
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[*] posted on 25-8-2008 at 09:03


Put not your faith in patents!

Do these patents cite any references to the primary literature that can be examined and evaluated?

That is where you will either find preperative details, or nowhere.

Failing that all you can do is experiment on your own but IMO you are chasing a phantom reaction.

SO2Cl2 will not make Ac2O and neither will PCl3.

The SOCl2 and PCl3 will make AcCl and then you will not be able to cleanly seperate the mixture. If you do not believe me, try it yourself.

A modern chemistry book referenced an old paper, saying that dry distillation of anhydrous NaOAc and cyanuric chloride gave AcCl. So I dug out the old paper. The statement was true. But they neglected to mention the yield was 5%.

The devil is always lurking in the details.

[Edited on 26-8-2008 by Sauron]




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[*] posted on 25-8-2008 at 12:07


Quote:
Originally posted by Sauron
Put not your faith in patents!

Do these patents cite any references to the primary literature that can be examined and evaluated?


No, but when talking of AcCl or SOCl2 with GAA, Beilstein also cites: Centralblatt 1924 II, 1401; 1925 II, 92; Frdl. 14, 254, 1484. The last is a collection of patents, but Centralblatt is pretty basic.
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[*] posted on 25-8-2008 at 12:32


Centralblatt is the German predecessor to Chemical Abstracts. So the question is what was Centralblatt citing? Primary literature that can be obtained in full text? Patents? What?

Engager's postulate is about NaOAc and SOCl2.

Any method to generate AcCl that works, is fine. I say isolate the AcCl and then have your pick of its reactions to make Ac2). We have an embarassment of choice as to how to make AcCl. Make it. Purify it. Then use it.

Look at it this way: SOCl2 is at times a chlorinating agent and at times a dehydrating agent. Is it dehydrating AcOH to Ac2O? No. It is chlorinating AcOH to AcCl. Period, end of story for SOCl2, it is gone as SO2 and HCl.

AcOH +SOCl2 -> AcCl + SO2 + HCl

Now with excess AcOH, the AcCl formed in first step reacts:

AcCl + AcOH -> Ac2O + HCl.

And you distill the Ac2O out of AcOH excess remaining. All byproducts are gaseous.

What happens with oxalyl chloride is quite different.

oxalyl chloride and 2 mols of a monocarboxylic acid form 2 HCl and a double anhydride which falls apart to the simple anhydride + CO + CO2.

Per Adams:

2 RCOOH + (COCl)2 -> (RCOOCO)2 + 2 HCl
(RCOOCO)2 -> (RCO)2) + CO + CO2

Adams says this is experimentally verified and many of the double anhydrides have been isolated.

The two equations can be unified as

2 RCOOH + (COCl)2 -> (RCO)2O + 2 HCl + CO + CO2

If you want the acyl chloride you must react the anhydride with more oxalyl chloride.

If instead of AcOH, NaOAc is used, the reaction proceeds as follows:

Equimolar ratios give AcCl and NaCl and CO and CO2

MeCOONa + (COCl)2 -> MeCOCl + CO + CO2 + NaCl

If 2 mols NaOAc are used per mol oxalyl chloride

2 MeCOONa + (COCl)2 -> (MeCO)2O + CO + CO2 + 2 NaClUnfortunately I don't see how this sheds any light on the reactions of SOCl2 with acetic acid or NaOAc.

For anhydride to form, the molar ration would be 2 acid to 1 SOCl2

2 RCOOH + SOCl2 -> (RCO)2O + SO2 + 2 HCl

Does this occur? Not one word in the JACS paper on SOCl2 rxns w/carboxylic acids.

AFAZIK it only occurs when CYCLIC anhydrides of DIBASIC acid are involved and the rings formed are 5 or 6 membered.

Succinic, glutaric, maleic and phthalic acids react this way with SOCl2. BUT NOT MONOCARBOXYLIC ACIDS.

Obviously the stoichiometry for attempted prep of a acyl duchloride requires twice as much SOCl2

HOOCCH2CH2COOH + 2 SOCl2 -> Succinic anhydride + 2 HCl + SO2 + 1 SOCl2 unreacted

That is, even if you use enough SOCl2 to make succinyl chloride, all you will get is succinic anhydride, by abstraction of one mol H2O, and 1 mol SOCl2 unreacted.

It is possible to force the chlorination in some cases per KIyrides by use of catalyst ZnCl2, to give phthalyl chloride from phthalic acid or anhydride for example.

I know of no catalyst for drive SOCl2 to make acyclic acid anhydrides.

Adams says the oxalyl chloride reaction works better with sodium salts of carboxylic acids than with the free acids.

We can hope the same is true for SOCl2 but we can't surmise it with so little basis in the literature. Not unless and until we test experimentally.

Let's work out the stoichiometry first.

NaOAc + SOCl2 -> AcCl + SO2 + NaCl

2 NaOOCMe + SOCl2 -> (MeCO)2O + SO2 + 2NaCl

At least those balance. I would suggest doing this in toluene as solvent. Warm the mixture till no more SO2 comes off. You should have a ppt of NaCl. Filter it off. Now distill the product from the solvent. A good column and you will be able to tell what you have by bp.

If NaOAc is not dry all you do is make SO2 and HCl reducing the effective amount of SOCl2.







[Edited on 26-8-2008 by Sauron]

[Edited on 26-8-2008 by Sauron]




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[*] posted on 26-8-2008 at 05:35


Preparation of Ac2O from thionylchloride was successful, here is description of my experiment:

120 ml of glacial acetic acid was added to 144 ml of thionylchloride, reaction takes place on mixing, leading to formation of HCl+SO2 and mixture is strongly cooled (endotermic reaction). Mixture is allowed to stand at room temperature for 2 hours, allowing most of HCl and SO2 to evolve. Next, reaction mixture is placed on water bath under efficent reflux condenser, tubing was tightly attached to end of condenser to vent reaction gasses to outside, bath was heated to 55C and mixture is left at this temperature for 2 hours. During this period convertion of acetic acid to acetylchloride is fully completed, and gas evolution ceases. Reaction product was cooled to room temperature and then in ice bath, 160g of freshly melted pulverized sodium acetate was added with stirring. Addition rate is adjusted, to not allow reaction mixture to boil. After acetate is added mixture is allowed to stand for 30 minutes at room temperature and was destilled. All liquid phase from reaction mixture is distilled off in temperature interval about 4C (about 136-140C), about 200 ml of distillate is obtained witch is acetic anhydride. Yield was not precisely mesasured but it is close to that predicted by theory. Reaction equations:

SOCl2 + CH3COOH => CH3COCl + HCl + SO2
СH3COCl + CH3COONa => (CH3CO)2O + NaCl

[Edited on 26-8-2008 by Engager]




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