Sauron
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Methanesulfinic Acid and Halogenated Derivatives
Alkanesulfinic acids are lower oxo acids of sulfur with an alkyl group attached.
R-S(=O)-OH
Very simple molecules, but how the hell are they made?
Oxidation of a thiol? Ugh, methyl mercaptan, not a fun idea. But this is actually one of the known methods.
I am interested in a general route to these and to halogenated variants such as chlorofluoromethanesulfinic acid.
Alkylsulfinic acids seem to be a lot more obscure than the corresponding alkylsulfonic acids. In fact it turns out that the alkylsulfonic acids are a
starting material for these products, by way of reduction with Zn dust in alcohol. I am tracking down a few leads and will report what I find.
In the older lit. the term "methylsulphinic acid" predominates.
Anyone have any knowledge of these?
[Edited on 3-2-2007 by Sauron]
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leu
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These compounds have been made by the reduction of sulphonyl chlorides with zinc or sodium sulphite, by the action of sulfur dioxide on zinc alkyls or
magnesium alkyl halides and by cleavage of ethylene disulphones with alkalis or cyanides 
Chemistry is our Covalent Bond
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Furch
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Indeed... From the mere look of its structure, I would say that the most feasible way to produce it would be from the actio of an organometallic
compound (Grignard or alkyl lithium) on sulphur dioxide.
Reaction oughta occur a la Grignard reagent on carbon dioxidide to yield given carboxylic acid, thusly:
RMgX + CO2 --> R-COOMgX -H+-> ROOH
And in the same fashion the alkanesulfinic acid should be had:
RMgX + SO2 --> RSOOMgX -H+-> RSOOH
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Sauron
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Thanks guys. The situation seems quite straightforward for the simple case of the unsubstitutes acid. Methanesulfonic acid or its chloride are easy to
buy. I have nt found a single instance of a halogenated or dihalogenated methanesulfonic acid, except for trifluoromethanesulfonic acid, which is not
what I am after.
This suggests that one would have to halogenate the methanesulfinic acid after reduction. Certainly in the case of zinc dust/alcohol reduction I would
expect the methyl Cl to be stripped off.
While in principle the stepwise chlorination and fluorination could be done, it would be a pain to perform, and I am hoping to find something a
little more elegant.
One old approach is to reduce trichloromethyl sulfenyl chloride (perchloromethyl mercaptan) then oxidize it to the acid. The starting material is a
waste product and a nasty one, from the chlorination of CS2 to CCl4. I would be happy if I could limit the declorination to removal of a single
cchlorine and then, after the oxidation, exchange one of the two remaining chlorines for a F.
In case you are wondering what the interest is, the sodium salt of halogenated (and probablt -un) methanesulfinic acids can be converted under quite
mild conditions by H2SO4, KNO3 and NaNO2 into the corresponding nitrosomethanes in high yield. (1930s)
A much more contemporary process c.1990 involves nitration of 1,2dichloro-1.2-difluoroethylene, hard to come by these days, to produce
chlorofluoronitroacetic acid, which upon treatment with red fuming nitric acid gives the chlorofluoronitrosomethane.
I am trying to elucidate how the Russians are making this stuff, which they are, and that double nitration does not look like fun.
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Sauron
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Here's the contemporary rxn scheme to make the same nitrosomethane intermediate. The problem is, how to buy the CFC starting material these days? Not
so simple. Making it means replicating Swatz's work from 110 years ago and lo and behold - in this country tetrachloroethylene is banned.
And that is why I am looking for other routes.
[Edited on 3-2-2007 by Sauron]
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Sauron
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Any of the several routes to the methanesulfinic acids or methanesulfonic acids that start from halomethanes like bromomethane or iodomethane, are
facile enough for the unsubstituted example.
But what about the chlorofluoromethanesulfinic acid target?
That would mean starting with chlorofluorobromomethane or chlorofluoroiodomethane. Not exactly off the shelf!
The initial formation of the Grignard reagent (or zinc alkyl) from such a species would probably proceed as desired toClFCH2MgI but then I'd expect
some side reactions to form ethane rather than the coupling with SO2, but hopefully the rates would be different enough to keep this down to a dull
roar.
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Sauron
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Loew, Zeit. f. Chem., 1869, p. 82
CS2 oxidized with potassium dichromate in presence of nitric and hydrochloric acids forms methanesuulfonyl chloride. I mention this mostly for those
who want to make their own reagents.
Methanesulfonyl chloride, which can also simply be purchased, can be reduced as described by @Furch and @Leu above.
However for my purposes the best procedure appears to be to make use of trichloromethyl sulfenyl chloride, which I will have anyway as byproduct of
making my own CCl4 from CS2 and Cl2 over activated carbon. Normally the CCl3SCl is a nasty waste product good for little besides making into
thiophosgene (which is useful.)
The trichloromethyl sulfenyl chloride is reduced with sodium amagam to methanesulfonyl chloride. I would like to find a more selective and milder
reducing agent, I'd like to be able to end up with dichloromethanesulfonyl chloride.
From there, two steps:
1. Replace one Cl with F
2. Reduce to the sulfinic acid without dechlorinating the methyl group. @Leu suggests sodium sulfite. That makes sense.
-------
Hmmm. How about bromoform or iodoform as starting materials to get to the methyl halides? Replacing two of the Br on bromoform with Cl and F ought to
be easy enough. Same with iodoform. I guess the tricky part will be to avoid replacing all the heavier halogens.
BTW the Grignard route, once the appropriate alkyl halide is obtained, is vis the reaction with sulfuryl chloride to give the methanesulfonic chloride
which is then reduced to the methanesulfinic acid. This is unsurprising since sulfuryl chloride is really just an adduct of SO2 and Cl2.
[Edited on 3-2-2007 by Sauron]
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Sauron
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I have concluded that the methanesulfinic acid route is not required for the purposes I had in mind, but I did uncover a number of interesting ways to
produce the alkylsulfonic acid and their chlorides and the corresponding sulfinic acids. These are in addition to the suggestions and input from
fellow members above.
Alkyl halides to alkylthiosulfate sodium salts, by treatment with sodium thiosulfate. Chlorination gives alkylsulfonyl chlorides.
Alkyl halides to alkylisothiouronium salts (by treatment with thiourea), chlorination gives same product as above.
Both are a lot less hassle than a Grignard prep not to mention having to prepare sulfuryl chloride.
Oh, and as an aside:
Heating methanesulfonyl chloride, which is both OTC and easily prepared, produces two things:
Phosgene
and
Thionyl Chloride.
The former is readily made by other means but SOCl2 is a pain to make. If someone absolutely needs SOCl2 this is a decent way to get there.
I only know of one other good way:
PCl3 + ->SO2Cl2 = POCl3 + SOCl2 (AC as catalyst)
But this obliges you to prepare PCl3 and sulfuryl chloride, doable but not so convenient. It does have the virtue of yielding (after fractionation)
POCl3 and SOCl2, both useful.
However there are far easier ways to POCl3 and very viable alternatives to SOCl2 for many purposes.
[Edited on 5-2-2007 by Sauron]
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Klute
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| Quote: |
Alkyl halides to alkylthiosulfate sodium salts, by treatment with sodium thiosulfate. Chlorination gives alkylsulfonyl chlorides.
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This seems very interesting. Sauron, do you have some refs on this? I can't acces the library for a while now..
I guess chlorinating arylthiosulfate sodium salts would equally yield the corresponding sulfonyl chloride?
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LSD25
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| Quote: | Originally posted by Sauron
... Oh and as an aside:
Heating methanesulfonyl chloride, which is both OTC and easily prepared, produces two things:
Phosgene
and
Thionyl Chloride.
The former is readily made by other means but SOCl2 is a pain to make. If someone absolutely needs SOCl2 this is a decent way to get there...
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Do you have ref's for this? I am seriously interested as methanesulfonyl chloride is a hell of a lot closer to OTC (via regulatory status) than bloody
thionyl chloride. I know of at least two decent routes to methanesulfonyl chloride and no decent routes to thionyl chloride, so yes, I am interested.
Whhhoooppps, that sure didn't work
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Sauron
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If you look at the date on that post you will understand why I do not immediately recall where I found that information.
Anyway the downside to this route is having to get rid of (or store) the phosgene.
If you just want SOCl2 there is a better way.
Benzotrichloride and phthaloyl chloride in presence of ZnCl2, 20 hours at 200 C in an autoclave. Gives almost quantitative conversions to phthaloyl
chloride and benzoyl chloride.
Phthaloyl chloride can also be purchased.
Phthaloyl chloride reacts with SO2 (dry) to give SOCl2.
I posted the JACS article by Thomas Kyrides about this some time back. UTFSE on phthaloyl chloride and you should find it quickly.
Sic gorgeamus a los subjectatus nunc.
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Sauron
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The above should read: "benzotrichloride and phthalic anhydride..."
Anyway len1 has cast some doubt on this reaction. He could not replicate Kyrides' result.
I think it is still worth another look, though. Kyrides was a reputable chemist from a large well known company (Monsanto.)
Sic gorgeamus a los subjectatus nunc.
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