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Author: Subject: Question about SO2 generation
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[*] posted on 12-3-2022 at 13:12
Question about SO2 generation

I'm currently trying to make some sulfuryl chloride (SO2Cl2), which can be made by reacting SO2 and Cl2 on some activated carbon.

The Cl2 generation is no problem, but I'm having some trouble with how I'm trying to make SO2.

I thought that since Na2S2O3 + 2HCl -> SO2 + H2O+2NaCl + S, I can generate the SO2 by dripping hydrochloric acid onto sodium thiosulfate. Unfortunately the rate of gas generation pretty slow and only even gets noticeable when the flask with the hydrochloric acid and sodium thiosulfate is heated up. I'm not heating to boiling, but I still wonder if much of the gas I'm seeing is just HCl that's coming out of the hydrochloric acid. I don't think it'll interfere with the reaction though. Some must be coming out though, because I can see small droplets of SO2Cl2 in the reactor (its formation is actually really exothermic...)

Does anybody know any troubleshooting for SO2 generation with this method?
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[*] posted on 12-3-2022 at 13:28

The droplets you see, most likely are not SO2Cl2, but a dilute mix of H2SO4 and HCl.

You need absolutely dry gases. Any water will lead to formation of H2SO4 and HCl in a very exothermic reaction.

Making SO2 is easy with Na2S2O5 (sodium metabisulfite) or K2S2O5. The use of Na2S2O3 is not recommended. The reaction is slow and it produces lots of side products (among them certain thionic acid and also H2S), which you notice in its smell. The gas mix produced from Na2S2O3 has a foul odor, due to the presence of other sulfurous compounds besides the SO2. If you use Na2SO3, or even better, Na2S2O5 (available from companies, which sell materials for making wine and beer), then you'll notice a very pungent, but much less foul smell.

Making SO2 can best be done by dripping 50% H2SO4 on Na2S2O5 and gently heating (to 60 C or so). The gas then needs to be dried very well, before it is mixed with Cl2.

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