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Author: Subject: Acetic anhydride preparation
Pulverulescent
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And you don't actually need GAA!
Ketene and water will work if you don't mind waiting a bit longer for the anhydride!

P
Fleaker
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Yes, but I would just start with GAA as a time saver. When I attempted this, the water in my second absorber column was indeed acidic after the reaction (in fact, I titrated it to find out how much ketene made it into that bubbler, looking back, I should probably have done an iodoform test too!).

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Pulverulescent
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It'll be Autumn before I can attempt the ketene, or any other route (blasted major home-improvement project!).

I'll probably go with copper tubing, brazed or copper eutectic joints, and electrically heated, to see how well it works.

'Only problem seems to be the lifetime of repeatedly heated copper tubing.

It still should be easier than an Ace-type lamp, at any rate!

And since I have GAA I won't be using water either.

BTW, Fleaker, how well did your ketene synth go, and what method did you use?

P
Ephoton
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I always found ketene to be a problem not due to its manufacture but just becouse
it does not fully react with the GAA. the problem being that it then bubbles out of the
acetic acid and either gets waisted in another wash bottle or goes into the enviroment.

I would think though it would react very quickly with HCl to form acetyl chloride.
this might be a way to make the whole ketene lamp a little safer.

I always found ketene very easy to make.
just a little expensive on equipment and hard on nichrome wire.

bash-2.05#

not_important
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It need not be wasted. Set up a train of water filled wash bottles, perhaps with a drop of H2SO4 in them as well. Ever so oft check the concentration of AcOH in the first and second bottles. At some point the first bottle will be somewhere between nearly 100% GAA and GAA+Ac2O. Add a new bottle to the end of the train, remove the first as on the next run the now GAA bottle will be making anhydride.

Using something more effective than ordinary wash bottles really helps with the problem of unreacted ketene. There were several examples of such given earlier in this thread; basically use a packed fractionation column for the absorber.
Pulverulescent
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Could someone please post pictures of their ketene-generator---I'd love to see them!

'Such a long thread, but no pics!

Fingers crossed, guys!

Thanks!

P
Foss_Jeane
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I found a couple of ketene generators. The first is sort of an afro-tech method.

Ghetto Ketene Generator

This one is really dangerous, and I wouldn't fool with it under any circumstances.

Here's a "ketene lamp" without the associated glassware. I'd like to get ahold of one of these since I collect funky old electronics.

Ketene Lamp

The latter might be OK to operate if you could set it up way out in the boonies and operate it by remote control at least a quarter mile upwind of the thing.

It would be bad enough if ketene were simply a nasty chemical that made irritating acetic acid when it comes in contact with moist eyeballs and/or nasal pasages. A good fume hood would take care of that. However, this stuff is way more toxic than that. As if that weren't bad enough, this is also one of the few substances that are known cancer-causers. No maybe's about that. You don't want stray molecules of this stuff floating around your basement.

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Polverone
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Can I get a literature reference on ketene being a known human carcinogen? Sauron mentioned this earlier, but a few minutes with Google doesn't turn up any references indicating that it is a known or probable human carcinogen. In fact some references (e.g. "Risk Management for Hazardous Chemicals" by Jeffrey Vincoli) explicitly state that ketene exposure has not demonstrated carcinogenic effects. Kirk-Othmer says the same thing about carcinogenic effects (none demonstrated). The Health Council of the Netherlands likewise reports no known carcinogenic effects in a 2001 report.

PGP Key and corresponding e-mail address
joeflsts
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 Quote: Originally posted by Polverone Can I get a literature reference on ketene being a known human carcinogen? Sauron mentioned this earlier, but a few minutes with Google doesn't turn up any references indicating that it is a known or probable human carcinogen. In fact some references (e.g. "Risk Management for Hazardous Chemicals" by Jeffrey Vincoli) explicitly state that ketene exposure has not demonstrated carcinogenic effects. Kirk-Othmer says the same thing about carcinogenic effects (none demonstrated). The Health Council of the Netherlands likewise reports no known carcinogenic effects in a 2001 report.

Agreed, in fact most literature claims longer term exposure to bring on pulmonary edema.

Joe
Foss_Jeane
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^^^^

It looks like that may have come from Wikipedia. There are some mentions of possible links to non-Hodgkin's lymphoma, though the link to ketene specifically doesn't appear to be established. Looks like something that was once thought to be the case, but turned out it really wasn't after further consideration.

Still, it's pretty darned toxic, and I wouldn't want to try running that ketene lamp inside, even with a fume hood.
stygian
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Here's a thought.

I'm not sure of their structure but could a carboxylic-carbonic anhydride be decarboxylated to yield a dicarboxylic anhydride?
Jome
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What do you mean, like pyruvic anhydride?
12AX7
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Carbonic? Would that be R-C(=O)-O-C(=O)-OH (or -O(-))? That would surely decarboxylate instantly.

Tim

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Sauron
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I have not been able so far to locate the page in my limited number of Org.Syn. annual volume hard copies from the 60s and 70s that contained the listed of proven human carcinogens, encompassing ketene.

I believe this was an OSHA list but that is going by memory and may be mistaken. I am quite certain ketene was on the list because I made note of the fact within the last few years.

HOWEVER, even if I find it, it would certainly appear to be the case that 30-40 years later, expert opinion has shifted and ketene is no longer regarded as a proven or even suspected human carcinogen.

If you examine the record over that many decades the experts appear to dither and waffle about what is and is not carcinogenic quite a bit.

Frankly this does not inspire great confidence in such "expertise", does it?

It rather implies that there have been rushes to judgement, later backpeddling, and in some cases reversals of the backpeddling.

A further implication is that carcinogenesis is still far from being well understood, and that includes chemical carcinogenesis.

As to the operation of a traditional ketene lamp such as described in Org.Syn., and various references, and formerly sold commercially by Ace Glass, I would not hesitate to perate one in a very well ventilated location such as in a fume hood that has been tested and shown to be well designed and have adequate face velocity and an appropriate scrubber system. One simply needs to appreciate that this is a small scale generator and can't be scaled up. A tube furnace type generator is scalable but now you are talking about a lot more risk.

[Edited on 10-6-2008 by Sauron]

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LSD25
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I take it most people here are at least aware of the proposed or cited synthesis of AA from methanesulfonyl chloride and triethylamine cited on Rhodium's site?

Well, here is a variant on the theme, toluenesulfonyl chloride (the bromide is reuseable and can be regenerated according to a procedure elsewhere, so what about the chloride?) in excess is added to sodium acetate (I suspect dry) and then heated to 180-200C for 30min. No need for amines, just the sulfonyl chloride...

http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3...

(It is on page 2 of the PDF)

Could something similar be done with methanesulfonyl chloride do you think?

Also, on another track, phthalic anhydride is mixed with GAA and sodium acetate in order to prepare cellulose acetate phthalate. Doesn't this suggest the formation of at least the mixed anhydride? So if one mixed GAA with phthalic anhydride and sodium acetate, is it possible to prepare AA comparatively simply (especially given that the phthalic anhydride is regenerable with heat)?

[Edited on 12-6-2008 by LSD25]

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Sauron
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There is no shortage of Ac2O preps involving anhydrous (fused) NaOAc.

The one you cite appears to employ tosyl chloride as a chlorinating agent to convert part of the GAA to acetyl chloride, which then reacts with the NaOAc to form Ac2O.

No surprises here.

The problem seems to be that many people simply cannot efficiently prepare properly anhydrous sodium acetate. The detailed instructions have been given here many times. The anhydrous sodium acetate is commercially available as well, from reliable vendors.

If starting from the hydrated salt, the fusion needs to be done twice, the second, higher temperature stage being the one that usually gets overdone, resulting in carbonization.

If you start with the freshly opened commercial anhydrous material, a single melt will suffice, and in the case of the Merck "super dry" grade may be superfluous.

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LSD25
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I thought I'd add in some interesting details of the preparation of the MsCl - not because it is off-topic - but because of the by-product(s) of performing this reaction in different solvents

The attached material contains 4 separate articles which have been condensed down

So Sauron, you'd agree that the MsCl should also give the anhydride from the salt and the anhydrous acid? So some thought on the preparation of MsCl from such a ubiquitious solvent as DMSO should be of some interest? What about AcCl (a byproduct of performing the rxn in GAA) or CCl4 (doing the rxn in CH2Cl2)... The best route (in terms of lack of byproducts and yield) appears to be 1:1 AcOH:H2O, where the intermediate chlorosulfone is hydrolysed in-situ giving predominantly the MsCl as the product.

[Edited on 13-6-2008 by LSD25]

Attachment: MsClfromDMSO.pdf (2.3MB)

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Sauron
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I believe there are serious toxicity issues with mesyl chloride that do not apply to tosyl chloride.

I see absolutely no advantage to using either one to obtain acetyl chloride (in situ, or isolated) as compared to the numerous other methods that have been elucidated for preparing that acyl chloride and other acyl chlorides.

My point in my last post above was that lots of people appear to come to no joy when trying to get anywhere with reactions of anhydrous sodium acetate. Therefore until that problem is solved, rehashing old stuff from rhodium that calls for anhydrous sodium acetate is just spinning of wheels, isn't it?

There are preps of Ac2O that do not rely on anhydrous NaOAc, and no I do not mean using ketene.

Oxalyl chloride, for example.

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not_important
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 Quote: Originally posted by LSD25 Well, what is the problem with anhydrous sodium acetate? Here is a decent step-by-step: http://www.instructables.com/id/S1HFXYZFA190FOL/

Which makes the tri-hydrate, not the anhydrous acetate.
LSD25
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not_important, I do realise that but I was actually in the middle of the post - I'd posted what I had cos my connection is utter crap at present and was in the middle of editing the same in order to add in the additional ref's. Unfortunately your post tried to quote part of a post which was in the process of being edited and the database/server didn't like it

I will now paraphrase what I had above

The sulfuric acid apparently causes some charring and I want to try phosphoric acid for this, but it apparently still does work (plus, I don't like wasting H2SO4).

[Edited on 13-6-2008 by LSD25]

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Sauron
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We are going around in a circle regarding anhydrous NaOAc.

The procedure for drying NaOAc.3H2O by fusion has been posted previously, in far more detail than that little clip from Feiser, and with illustrations, the source having been Gattermann. The problem is not reading about doing it. The problem IS doing it, on a decent scale and not charring it.

Gattermann states that a single fusion suffices for the comml anhydrous salt which might have readsorbed some moisture in storage. This sounds more productive to me, but people still seem to try to go from the trihydrtae for reasons of (false) economy, and they upgefuck.

I have yet to see anyone post success with this step.

As to the chlorination of DMSO, I will take another look at this reaction. I note that the reaction is said to be closely akin to the chlorination of (among other things) MeSCN, which I have posted about elsewhere. Also one reported product is trichloromethyl methyl sulfide. It is easy to see how this can fragment to CCl4 via the well known trichloromethyl radical; IMO it would be a mistake to assume that CCl4 was only forming from chlorination of DCM solvent, particularly as no CHCl3 is mentioned as being formed as well.

Another feedstock for prep of MsCl is S-methylthiouronium sulfate, the methylated derivative of thiourea. The relationship to methyl thiocyanate is again obvious.

Another starting material is sodium methyl thiosulfate. This is from methylation of the ubiquitous sodium thiosulfate, readily available OTC from photographic suppliers. ("Hypo")

[Edited on 14-6-2008 by Sauron]

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Sauron
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 Quote: Originally posted by LSD25 I take it most people here are at least aware of the proposed or cited synthesis of AA from methanesulfonyl chloride and triethylamine cited on Rhodium's site?

I saw a couple preps of mesyl esters on Rhodium but nothing about MsCl, TEA and GAA/NaOAc to make Ac2O.

Kindly provide URL or attach the pdf here.

I just spent more time than I really cared to reading four papers you posted, which generally had little to do with chlorination of DMSO (save for the first.) They had a lot to do with chlorination of sym-trithiane, chlorination of dialkyl sulfides, etc. The yields of mesyl chloride were at best only fair and nowhere did I see a viable preparative path to CHCl3/CCl4 or AcCl, which were side products.

Interesting chemistry but mostly off target if not off topic. Other processes are more straightforward, simpler, with less elaborate workups and much higher yields.

Now I will have a closer look at the tosyl chloride article. I have a kilo of tosyl chloride on hand, something I can't say presently for mesyl chloride. The latter is readily enough available, without any DMSO having to die for it.]

The tosyl chloride prep of Ac2O from anhydrous NaOAc, which does not require GAA, is in the paper cited by LSD25 and in irs Reference 4 (JACS 68, 2019, attached below) conducted on a very very small scale (< 1 ml product). The TsCl and dry NaOAc are admixed as solids, then heated 30 min at 180-200 C, at which temp they are most certainly a melt. Ac2O distills off. IF this process scales up, it will indeed be both simple and useful.

I'd think that an oil bath preheated to 190 C would be ideal. Minimize the time to get the pot to temp.

I think I have a bottle of anhydrous NaOAc, unopened, around. This rxn does not really need a hood. Let me see what I can do about trying this one out on a 100 g basis. Maybe not today or tomorrow but hopefully this month.

I just crunched the numbers from the Ac2O prep LSD cited and from the reference I pulled up.

The original prep used equimolar amounts of sodium acetate and tosyl chloride, and got a 90% yield of Ac2O. LSD25's paper employed about a 15% excess of tosyl chloride, and did not indicate their product amount. They were operating at a fraction of the already small scale of the original (7.5 mmols vs 22.3 mmols.)

Tosyl chloride melts at 65-69 C and boils at 134 C/10 mm Hg. Sodium acetate (anhydrous) melts with decomp. above 300 C. So the salt will either dissolve or be suspended in molten tosyl chloride at 180-200 C, and Ac2O will flash off as it forms. Sounds like a 1 liter pot will suffice for about a 2.2 mol run that ought to produce c.100 ml Ac2O. That is from 162 g sodium acetate and 425 g tosyl chloride.

ANyone care to work out the stoichiometry? Or even what the reaction looks like? Obviously two equivalents of acetate are needed to produce one of anhydride. But does AcCl form in situ and react with the acetate to form the anhydride? Or what? Is HCl going to evolve? TsOH left behind? Anyone have a clue?

[Edited on 14-6-2008 by Sauron]

Attachment: Ac2OfromTosylchloride.pdf (301kB)

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LSD25
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Yeah, whoops - I think the auto-condense procedure in Acrobat is to blame for part of that, I have accidentally condensed part of the collection with itself and other papers did not get added to the collection at all (write-protected).

Sauron, yeah the reaction is nowhere near as simple as could otherwise be suggested, in fact it is more than a little interesting. I note in fact that you advanced some varied hypotheses above for what was going on, so I thought you might have appreciated the author's of those papers views on the same.

However the suggestion that the majority of the papers don't actually deal with the chlorination of DMSO in aqueous acetic acid, misses the point somewhat:

 Quote: The complication involved in chlorinating more nucleophilic sulfides and sulfoxides is that the product is often nearly as reactive as the starting material. For example, chlorination of DMSO in aqueous acetic acid, at room temperature, leads to the formation of 1-chloro-2-thiapropane-2-oxide, 1, which is seriously contaminated with 1,l-dichloro-2-thiapropane-2-oxide. 2. This was taken from page 24/45 of the attached material (actually the study on the intermediate stages of the 'sulfohaloform reaction).

With that in mind, the repeated references to starting from this intermediate begin to make some sense, don't they? As to the remainder of the articles, particularly those which deal more with the specifics of the reaction than the product thereof, I have found it is important to at least make the effort to provide additional material (on this board and others) in order that other people can see where the idea comes from (and more especially, the concept underlying such ideas) - such left-field suggestions generally get pooh-poohed rather quickly otherwise

There are numerous studies on this reaction, apparently there was quite a bit of work carried out on the subject, for example:

 Quote: Mechanism of the photochemical chlorination of sulfones, Russian Chemical Bulletin, Springer New York (ISSN 1066-5285 (Print) 1573-9171 (Online): Volume 19, Number 9 / September, 1970: DOI 10.1007/BF00849770) Conclusions 1. The photochlorination of dimethylsulfone proceeds according to a radical-chain mechanism with cleavage of a C-H bond and formation of trichloromethylmethylsulfone as the only product. 2. Photochlorination of diethylsulfone at the first step also proceeds with cleavage of a C-H bond, but the radical C2H5SO2CH2CH2 formed in this case is stabilized by cleavage of a C-S bond, forming ethylene and the radical C2H5SO2. 3. Photochlorination of methylphenylsulfone proceeds according to a mechanism analogous to that for diphenyl- and dimethylsulfones. 4. Photochlorination of sulfolane proceeds according to a radical-chain mechanism with cleavage of the C-H bond at thebeta-carbon atom, forming 3,3,4,4-tetrachlorosulfolane as the final product. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2029–2032, September, 1970.

Now that would be interesting as I think that is one of the intermediates in the MsCl synthesis and MSM is cheap as shit.

As to the Rhodium.ws reference, it is a page I know you are familiar with (at the bottom).

 Quote: A Mild Method for the Synthesis of Carboxylic Anhydrides General Procedure, exemplified for Propionic Anhydride: Propionic Acid + Methanesulfonyl chloride --Et3N--> Propionic Anhydride To a stirred solution of propionic acid (2 mmol) and methanesulphonyl chloride (1.05 mmol) in dry THF (10 ml) at -15°C under nitrogen was added triethylamine (3.5 mmol) in THF (5 ml) slowly over 20 minutes. After stirring 1 hour at -15°C the reaction mixture was allowed to warm to room temperature. The reaction mixture was filtered through Celite and the solvent was evaporated off under reduced pressure. The anhydride was isolated by short-path distillation (yield: 85 %, bp: 70-72°C / 20 Torr (lit. bp: 67.5°C / 18 Torr)). Reference: "A mild method for carboxy-group activation and synthesis of carboxylic anhydrides", J. Chem. Research 100 (1984) This method is fairly general. The authors prepared several anhydrides, in good to excellent yield. There are two methods of isolation (used depending on the anhydride made). Method of isolation A The solvent was evaporated under reduced pressure and the residue was partitioned between ether or ethyl acetate (50 ml) and a cold saturated solution of sodium hydrogen carbonate (50 ml). The organic phase was washed successively with saturated sodium hydrogen carbonate solution and brine, dried (MgSO4), and concentrated in vacuo to afford the anhydride. Method of isolation B (implemented in the propionic anhydride synthesis) The reaction mixture was filtered through Celite and the solvent was evaporated off under reduced pressure. The anhydride was isolated by short-path distillation. Synthesis of internal anhydrides To a stirred solution of phthalic acid (0.332 g, 2 mmol) in dry THF (12 ml) was added triethylamine (0.202 g, 2 mmol) under nitrogen. The reaction mixture was cooled to - 20 °C. After stirring for 15 minutes, methanesulphonyl chloride was added (0.24 g, 2.1 mmol) followed by triethylamine (0.404 g, 4 mmol) in THF (5 ml) over 15 minutes. The reaction mixture was stirred at -15°C for 2 hours. The product was isolated using method A (0.275 g,, 93 %, m.p. 130-131°C) Other Examples Acid: MeCH=CHCOOH Yield anhydride: 87% Method of isolation: B Acid: PriCOOH Yield anhydride: 89% Method of isolation: A Acid: Me(CH2)7CH=CHCOOH Yield anhydride: 95% Method of isolation: A Acid: PhCOOH Yield anhydride: 92% Method of isolation: A Acid: 4-O2N-C6H4COOH Yield anhydride: 82% Method of isolation: B Acid: PhCH=CHCOOH Yield anhydride: 85% Method of isolation: B Acid: 4-MeO-C6H4COOH Yield anhydride: 94% Method of isolation: B Acid: 2-Cl-C6H4COOH Yield anhydride: 93% Method of isolation: A

[Edited on 14-6-2008 by LSD25]

Attachment: PreparationandmechanicsofMsClfromDMSO.pdf (2.7MB)

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Sauron
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No, I did understand where Clayton was going with his chlorinations in various aqueous and nonaqueous solvents and divers substrates. One could hardly miss the significance.

Thanks for the ref from rhodium. Interesting that the MsCl reaction calls for TEA. On the other hand these are proceeding from the acids not the carboxylates.

Just as the chlorinations diverse with and without the presence of water in the cases of the sulfoxides, sulfides etc, they also differ with and without water in the case of alkyl thiocyanates.

Mesyl chloride being the major product when water is present.

See

1.

The Action of Chlorine on Thiocyanates
Treat B. Johnson and Irwin B. Douglass
JACS 61 pp 2548 - 2550 (1939);

DOI: 10.1021/ja01878a085

2.

Explosion Hazard in the Chlorination of Alkyl Isothioureas to Prepare Alkyl Sulfonyl Chlorides
Karl Folkers, Alfred Russell, and R. W. Bost
JACS 63 pp 3530 - 3532 (1041);

DOI: 10.1021/ja01857a510

Or just hang on a wee bit as I am requesting these in References.

The second is a reminder than these chlorinations can get nasty.

Mesyl chloride is also formed in the aqu chlorination of s-methyl thiouronium salts, but Merck had a nasty kaboom! while doing so.

At that time everyone was working on preps for these reagents because of the great interest in sulfa drugs at start of WWII.

While MeSCN can't compete with DMSO for economy, it is certainly a closely related reagent, you can regard it as a dehydrated methylsulfonic acid (almost). Traditionally mesyl chloride was prepared by brute force chlorination of methanesulfonic acid with PCl5, which was costly and inefficient. SOCl2 was also used with better results.

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Sauron
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I hate to be a spoilsport but, have a look at the relative complexity of the reaction conditions for the MsCl prep of anhydrides.

THF solvolysis
Cooling -15 C
N2 atmosphere

And all that for a measly 2 mmol scale. To operate on a mere 1 molar basis 500x volume of THF would be needed with requisitely larger vessel.

Now compare this to the elegant stark simplicity of the tosyl chloride procedure. (Also unearthed by you.)

No solvent
No inert atmosphere
No elaborate workup - anhydride distills off in case of acetic anhydride

Now, are we going to believe that someone who can't get tosyl chloride, can get a lot of THF?

The tosyl chloride procedure is clearly better, more amateur friendly.

This observations renders all the DMSO chlorination material academic. At least in my opinion.

Wouldn't you agree?

PS

For those of us who buy our reagents both tosyl chloride and mesyl chloride are cheap.

Acros prices:

Tosyl chloride 2 Kg $88 (about 10 mols) Mesyl chloride 1 L (1500 g)$100 (13 mols)

The cost per mol is about same.

Obviously for those who must DIY, mesyl chloride will be easier to build, unless one has a surfeit of chlorosulfonic acid.

[Edited on 14-6-2008 by Sauron]

[Edited on 15-6-2008 by Sauron]

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