Chlorosulfonic acid

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Structural formula
Structural formula of chlorosulfonic acid
Wedges to clarify the spatial structure
Surname Chlorosulfonic acid
other names
  • Chlorine (o) sulfuric acid
  • Sulfuric acid chlorohydrin
  • Sulfuryl hydroxyl chloride
Molecular formula HSO 3 Cl
Brief description

colorless to yellowish, pungent odor, hygroscopic liquid

External identifiers / databases
CAS number 7790-94-5
EC number 232-234-6
ECHA InfoCard 100.029.304
PubChem 24638
Wikidata Q411060
Molar mass 116.53 g mol −1
Physical state



1.75 g cm −3 (20 ° C)

Melting point

−80 ° C

boiling point

152 ° C (with decomposition)

Vapor pressure

0.45 h Pa (20 ° C)


violent decomposition in water

Refractive index


safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
05 - Corrosive 07 - Warning


H and P phrases H: 314-335
EUH: 014
P: 261-280-305 + 351 + 338-310
Toxicological data

50 mg kg −1 ( LD 50ratoral )

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Chlorosulfonic acid or chlorosulfonic acid (HSO 3 Cl) is an incomplete acid chloride of sulfuric acid , in which only one hydroxy group of the sulfuric acid by chlorine is replaced. Chlorosulfonic acid is a colorless, pungent smelling liquid that smokes heavily in the air. The melting point is −80 ° C, the boiling point is 152 ° C. Like all acid chlorides, chlorosulfonic acid is very reactive; it reacts violently with water, converting it to sulfuric acid and hydrochloric acid .

Their effect as a fogging agent is based on the reaction with the air humidity , whereby a fog of sulfuric acid and hydrochloric acid is formed. This acid mist is very aggressive, it attacks metals and makes people cough , as well as organic substances ( wood , tissue ). In addition sulfur trioxide dissolved in chlorosulfonic acid, one obtains the fog acid , forms the even denser fog as chlorosulfonic acid. The use of chlorosulfonic acid as a smoke agent requires a sufficiently high level of humidity, which is why chlorosulfonic acid was primarily used in the navy . On the one hand because of the humidity, and on the other hand because the ship can move away from the mist and is therefore less exposed to its aggressive effects.


Chlorosulfonic acid can be represented by the action of phosphorus pentachloride on concentrated sulfuric acid:

Technically, chlorosulfonic acid is represented by introducing hydrogen chloride gas into liquid sulfur trioxide:


Chlorosulfonic acid is used in fog acid kegs to make fog acid.

Chlorosulfonic acid is also used as a smoke agent in the manufacture of chemical intermediates (introduction of the HSO 3 group into aromatic compounds). The aromatic is first chlorosulfonated with an excess of chlorosulfonic acid (introduction of the SO 2 Cl group into aromatic compounds) and can later be hydrolyzed to sulfonic acid in a targeted manner. In contrast to the sulfonic acids, the sulfonic acid chlorides are not water-soluble and are better suited for many reactions.

Furthermore, chlorosulfonic acid is used for the production of ion exchangers and the crop protection agents asulam , bentazon , carbophenothion , chlorfenson , famphur , flusulfamid , hexachlorobenzene , imazosulfuron , prosulfuron and tetradifon .

Individual evidence

  1. a b c d e f g h Entry on chlorosulfuric acid in the GESTIS material database of the IFA , accessed on February 14, 2017(JavaScript required) .
  2. Data sheet Chlorosulfonic acid from Sigma-Aldrich , accessed on January 21, 2020 ( PDF ).
  3. Entry on chlorosulphuric acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  4. Data sheet chlorosulfonic acid (PDF) from Merck , accessed on January 19, 2011.
  5. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 591.
  6. G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 385-386.
  7. R. Beckert et al., Organikum 22nd edition, Wiley-VCH 2004, p. 364.
  8. Thomas A. Unger: Pesticide Synthesis Handbook . William Andrew, 1996, ISBN 0-8155-1853-6 , pp. 1030 ( limited preview in Google Book search).