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Author: Subject: Thionyl chloride via the oxidation of SCl2 with a chlorate?
garphield
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[*] posted on 14-9-2021 at 22:42
Thionyl chloride via the oxidation of SCl2 with a chlorate?


The wikipedia article for POCl3 said that it can be prepared via the following reaction:

3 PCl3 + KClO3 -> 3 POCl3 + KCl

Would this work for SCl2 or no? It might be worth trying.
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[*] posted on 15-9-2021 at 00:22


The problem with that kind of given reactions on Wikipedia is that in many cases they have no practical meaning at all. If you mix PCl3 and KClO3 and apply some heat, then almost certainly there will be formation of POCl3, but I do not expect the reaction to run smoothly and nicely according to the given reaction equation. Besides POCl3 I expect a plethora of other compounds to be formed and any attempt at isolating the POCl3 from all other crap will be futile.

With SCl2 (and S2Cl2, which commonly is present as well) and KClO3 I also expect a reaction, and there may even be some SOCl2 in the reaction products, but I also expect SO2, maybe even some SO2Cl2, and of course also KCl, K2SO3, K2SO4, . . .

Synthetically practical reactions with solid oxidizers like KClO3 are very rare. Only when such an oxidizer is used in aqueous solution, it can act as a synthetically useful compound (e.g. in preparation of quinone from hydroquinone in acidic aqueous solution). Just mixing dry KClO3 with some chemical and then heating until the reaction starts usually will lead to a violent reaction (think of pyrotechnics) with a plethora of reaction products, which are released as a cloud of smoke and gas.




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clearly_not_atara
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[*] posted on 15-9-2021 at 05:58


The difficulty of producing SOCl2 by the oxidation of SCl2 has to do with finding an oxidizer that is, simultaneously:
(1) an oxygen transfer agent
(2) won't undergo nucleophilic displacement with SOCl2
(3) not able to oxidize SOCl2 to SO2Cl2
(4) won't explode under the conditions

Chlorate almost certainly fails (3) and might also fail (2). NO2, ClO2 and O3 also likely fail (3). Hydroperoxides fail (2) and symmetric peroxides probably fail (4). On the other hand, pyrosulfates might work:

Na2S2O7 + 2 SCl2 >> 3 SO2 + 2 NaCl + SOCl2

In this case you're really just wasting an extra equivalent of SCl2 so that you can form SO3 in situ. But that might nonetheless be simpler than trying to isolate SO3. Just because I can balance the equation doesn't mean it will work, though.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 15-9-2021 at 06:38


Pyrosulfate is not oxidizing and in-situ formation of SO3 requires HIGH temperatures. Na2S2O7 is not much more active than NaHSO4 and can fairly easily be made by heating NaHSO4 in order to drive off one molecule of water from two units of NaHSO4. You need to heat to a MUCH higher temperature to drive off SO3 and leave Na2SO4 behind. IIRC our passed away member magpie once made equipment for decomposition of Na2S2O7 and collected some SO3 succesfully. This was a great achievement, but it required considerable metalworking/engineering to make a suitable apparatus, which can withstand the required heat and corrosive materials.

Maybe Na2S2O8 can be used as oxidizer. That really is a strong oxidizer and only requires gentle heating to give off its oxygen. It also is a very cleanly acting oxidizer. I, however, just give this as a suggestion for further investigation, I have no personal experience in oxidizing SCl2 with dry Na2S2O8. Normally, Na2S2O8 is used in aqueous solution as a strong and cleanly acting oxidizer.




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[*] posted on 15-9-2021 at 06:55


There is reported in the old literature method of disproportionation of ClSO3 * SCl3 (SCl4 where one chlorine atom is replaced by the chlorosulfonic acid radical):
ClSO3 * SCl3 -> SO2Cl2 + SOCl2.

The starting compound could be prepared by the action of excess chlorine mixed with air on S2Cl2 and could be separated from the reaction products as a crystalline solid.

Probably this method is not a very practical one (according to the fact nobody ever mentioned it), but the mechanism of disproportionation looks like an important step in forming this compound (also according to what I read about SOCl2 chemistry). So, try to find conditions when it disproportionates.
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[*] posted on 15-9-2021 at 12:33


Quote: Originally posted by woelen  
Pyrosulfate is not oxidizing and in-situ formation of SO3 requires HIGH temperatures.

The reaction mechanism would have to start with pyrosulfate attacking SCl2 as a nucleophile. This isn't likely, but I don't see why it would be impossible. The resulting S-O-S-O-S bonded intermediate might undergo other reactions.

When I said "you can form SO3 in situ" I was referring to the fact that the oxidizer is really the "same" as the usual method (a sulfur (VI) oxide). I don't think the actual formation of molecular SO3 would be likely or necessary.

The big problem is that SCl2 isn't that great of an electrophile and S2O7(2-) is not that great of a nucleophile. Persulfate, if anything should be an even weaker nucleophile, by electronic considerations, methinks.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 15-9-2021 at 15:35


Quote: Originally posted by woelen  
The problem with that kind of given reactions on Wikipedia is that in many cases they have no practical meaning at all. If you mix PCl3 and KClO3 and apply some heat, then almost certainly there will be formation of POCl3, but I do not expect the reaction to run smoothly and nicely according to the given reaction equation. Besides POCl3 I expect a plethora of other compounds to be formed and any attempt at isolating the POCl3 from all other crap will be futile.


The preparation is in my scan of Biltz and Biltz. Also the 1909 (4th ed.) Gattermann, who states that the yield is at least equal to the weight of the PCl3 (citing J Prakt 28, 382 (1883), https://doi.org/10.1002/prac.18830280131). The famous Fritz Ullmann recommends doing this diluted with premade POCl3 to avoid explosive reactions, in Ber 34, 2172 (1901) (aka https://doi.org/10.1002/cber.190103402140) and says the yield is almost quantitative.

Needless to say, the reactions of P and P cpds. are not interchangeable with S.

[Edited on 16-9-2021 by S.C. Wack]




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[*] posted on 15-9-2021 at 16:16


.....there has been several threads on the discussion of this compound and it's various approaches like this one here....

https://www.sciencemadness.org/whisper/viewthread.php?tid=11...




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[*] posted on 15-9-2021 at 23:12


Quote: Originally posted by S.C. Wack  
The preparation is in my scan of Biltz and Biltz. Also the 1909 (4th ed.) Gattermann, who states that the yield is at least equal to the weight of the PCl3 (citing J Prakt 28, 382 (1883), https://doi.org/10.1002/prac.18830280131). The famous Fritz Ullmann recommends doing this diluted with premade POCl3 to avoid explosive reactions, in Ber 34, 2172 (1901) (aka https://doi.org/10.1002/cber.190103402140) and says the yield is almost quantitative.

Needless to say, the reactions of P and P cpds. are not interchangeable with S.

[Edited on 16-9-2021 by S.C. Wack]

That's quite interesting. Again an example of old literature, which looks very interesting. Normally, reactions involving dry solid oxidizers like KClO3, have no practical synthetic meaning, expect maybe production of O2. So, this example is quite remarkable.

Is it possible to share these scans (in the references section)?




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[*] posted on 16-9-2021 at 14:17


Well, I'm not sure that there's much reason to upload articles here when they are downloaded from sci-hub (.se at this time) after entering the doi there or directly placing it after the .se/. BTW the Russians (among others) seem not so fond of javascript, so it's not needed there or at libgen.rs, (unlike my current site and the previous sites over the years which very few have downloaded from, mostly only when someone else posted a link to specific books such as Vorobyova somewhere else) so one should enjoy such magnanimous sites without fear of javascript exploits.



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