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Chlorosulfonic acid

Deactivation needs a lot of resources

Chlorosulfonic acid develops a lot of fog when exposed to air and reacts very vigorously with water and even with ice explosively. During this reaction a lot of hydrogenchloride gas is formed. Old charges are often coloured brownish. Probably this is caused by corrosion of the bottle caps which often cannot resist for a longer period of time. (Have caps at hand for necessary replacement!) Since even traces of contaminations may give a considerable staining, a slightly colored liquid is probably not ruined!

Pure compound:

Dispose pure chlorosulfonic acid without any treatment as a separate bottle. Take care to pack it securely. Especially take care to use a proper and tight closing cap!


If you are going to perform the following deactivation consider that a lot of sulfuric acid and sodium hydroxide or sodium carbonate are needed as auxilliary materials. Therefore a deactivation is only meaningful, if disposing as a pure compond is not possible or if it happens that the auxilary materials are also waste materials.

Put the chlorosulfonic acid into a three-necked flask with a dropping funnel and a reflux-cooler (equipped with a gas outlet pipe) and add carefully 60 - 70 % sulfonic acid through the dropping funnel. With a lower concentration of the sulfonic acid the reaction becomes more vigorous. Lots of hydrogen chloride gas is formed. Use the pipe to absorb this gas. If you like to cool the reaction flask in an ice bath consider that in case of a breakdown of the flask all of the acid will have contact with water! If this happens at the beginning of the reaction, this will end in a desaster!

If the reaction is going to subside you should lower the concentration of the acid. At the end add pure water. Leave the mixture standing alone. Blow a little air through the apparatus to remove the acid gas before you open it. The resulting mixture is neutralized with sodium hydroxide or sodium carbonat (Watch the foam!) and then flushed down the drain. Be aware that there will be a precipitation of sodium sulfate because this salt is not very soluble in water.