Chlorosulfuric acid

Chlorosulfuric acid
Names
	IUPAC name Sulfurochloridic acid
	Other names Chlorosulfuric acid,; Chlorosulfonic acid,; Chlorosulphonic acid,; Chlorinesulfonic acid,; Chlorinesulphonic acid,; Chloridosulfonic acid,; Chloridosulphonic acid,; Sulfuric chlorohydrin
Identifiers
CAS Number	7790-94-5 ;
3D model (JSmol)	Interactive image;
ChemSpider	23040 ;
ECHA InfoCard	100.029.304
EC Number	232-234-6;
PubChem CID	24638;
RTECS number	FX5730000;
UNII	2O9AXL1TJ4 ;
UN number	1754
CompTox Dashboard (EPA)	DTXSID1029706 ;
	InChI InChI=1S/ClHO3S/c1-5(2,3)4/h(H,2,3,4) Key: XTHPWXDJESJLNJ-UHFFFAOYSA-N ; InChI=1/ClHO3S/c1-5(2,3)4/h(H,2,3,4) Key: XTHPWXDJESJLNJ-UHFFFAOYAO;
	SMILES ClS(=O)(=O)O;
Properties
Chemical formula	HSO3Cl
Molar mass	116.52 g mol−1
Appearance	colorless liquid, but commercial samples usually are pale brown
Density	1.753 g cm−3
Melting point	−80 °C (−112 °F; 193 K)
Boiling point	151 to 152 °C (304 to 306 °F; 424 to 425 K) (755 mmHg or 100.7 kPa)
Solubility in water	hydrolysis
Solubility in other solvents	reacts with alcohols; soluble in chlorocarbons
Acidity (pKa)	−5.9 (in CF3CO2H)
Refractive index (nD)	1.433
Structure
Molecular shape	tetrahedral
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H335
Precautionary statements	P260, P261, P264, P271, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 2 W; OX
Safety data sheet (SDS)	ICSC 1039
Related compounds
Related compounds	Sulfuryl chloride; Sulfuric acid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSO₃Cl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic and a powerful lachrymator. Commercial samples usually are pale brown or straw colored.^[3]

Salts and esters of chlorosulfuric acid are known as chlorosulfates.

Structure and properties

Chlorosulfuric acid is a tetrahedral molecule. Its structure was debated for many decades until in 1941 Shrinivasa Dharmatti proved by magnetic susceptibility that chlorine is directly bonded to sulfur.^[4]^[5]

The formula is more descriptively written SO₂(OH)Cl, but HSO₃Cl is traditional. It is an intermediate, chemically and conceptually, between sulfuryl chloride (SO₂Cl₂) and sulfuric acid (H₂SO₄).^[6] The compound is rarely obtained pure. Upon standing with excess sulfur trioxide, it decomposes to pyrosulfuryl chlorides:^[7]

2 ClSO₃H + SO₃ → H₂SO₄ + S₂O₅Cl₂

Synthesis

The industrial synthesis entails the reaction of hydrogen chloride with a solution of sulfur trioxide in sulfuric acid:^[7]

HCl + SO₃ → ClSO₃H

It can also be prepared by the method originally used by acid's discoverer Alexander William Williamson in 1854,^[4] namely chlorination of sulfuric acid, written here for pedagogical purposes as HSO₃(OH) vs. the usual format H₂SO₄:

PCl₅ + HSO₃(OH) → HSO₃Cl + POCl₃ + HCl

The latter method is more suited for laboratory-scale operations.

Williamson's discovery disproved then-popular hypothesis that sulfuric acid is a compound of water (which was incorrectly assumed to have formula of HO) and sulfur trioxide.^[8]

Applications

ClSO₂OH is used to prepare alkyl sulfates, which are useful as detergents and as chemical intermediates:^[7]

ROH + ClSO₃H → ROSO₃H + HCl

One historical synthesis of saccharin begins with the reaction of toluene with ClSO₂OH to give the ortho- and para-toluenesulfonyl chloride derivatives:

CH₃C₆H₅ + 2 ClSO₂OH → CH₃C₆H₄SO₂Cl + H₂SO₄ + HCl

Oxidation of the ortho isomer gives the benzoic acid derivative that then is cyclized with ammonia and neutralized with base to afford saccharin.

Chlorosulfonic acid has been used as an anti-contrail agent in Ryan Model 147 reconnaissance drones,^[9] and to produce smoke screens.^[10]^[11]

Safety

ClSO₃H reacts violently with water to yield sulfuric acid and hydrogen chloride, which are corrosive:

ClSO₃H + H₂O → H₂SO₄ + HCl

Related halosulfuric acids

Fluorosulfonic acid, FSO₂OH, is a related strong acid with a diminished tendency to evolve hydrogen fluoride.
Bromosulfonic acid, BrSO₂OH, is unstable, decomposing at its melting point of 8 °C to give bromine, sulfur dioxide, and sulfuric acid.
Iodosulfonic acid is not known to occur.

References

^ Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 32. ISBN 0-08-029214-3. LCCN 82-16524.
^ "New Environment Inc. - NFPA Chemicals".
^ Cremlyn, R. J. (2002). Chlorosulfonic Acid. Royal Society of Chemistry. ISBN 978-0-85404-498-6.
^ ^a ^b Kirk, Raymond Eller; Othmer, Donald Frederick (1964). Encyclopedia of Chemical Technology. Interscience Publishers.
^ Dharmatti, S. S. (1941-05-01). "Magnetism and Molecular Structure of Sulphur Compounds". Proceedings of the Indian Academy of Sciences - Section A. 13 (5): 359–370. doi:10.1007/BF03049293. ISSN 0370-0089.
^ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. pp. 549–550.
^ ^a ^b ^c Bergen, Elvira; Maas, J.; Baunack, F. (2024). "Chlorosulfuric Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_017.pub2. ISBN 3527306730.
^ "The Quiet Revolution".
^ Method and apparatus for suppressing contrails (PDF). United States Patent and Trademark Office. 1970.
^ The Royal Navy at War (DVD). London: Imperial War Museum. 2005.
^ Amos, Jonathan (2018-04-11). "Nazi legacy found in Norwegian trees". BBC News Online. Retrieved 2018-04-17.

[P82db-1] Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 32. ISBN 0-08-029214-3. LCCN 82-16524.

[2] "New Environment Inc. - NFPA Chemicals".

[3] Cremlyn, R. J. (2002). Chlorosulfonic Acid. Royal Society of Chemistry. ISBN 978-0-85404-498-6.

[:0-4] Kirk, Raymond Eller; Othmer, Donald Frederick (1964). Encyclopedia of Chemical Technology. Interscience Publishers.

[5] Dharmatti, S. S. (1941-05-01). "Magnetism and Molecular Structure of Sulphur Compounds". Proceedings of the Indian Academy of Sciences - Section A. 13 (5): 359–370. doi:10.1007/BF03049293. ISSN 0370-0089.

[6] Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. pp. 549–550.

[Ullmann-7] Bergen, Elvira; Maas, J.; Baunack, F. (2024). "Chlorosulfuric Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_017.pub2. ISBN 3527306730.

[8] "The Quiet Revolution".

[9] Method and apparatus for suppressing contrails (PDF). United States Patent and Trademark Office. 1970.

[10] The Royal Navy at War (DVD). London: Imperial War Museum. 2005.

[11] Amos, Jonathan (2018-04-11). "Nazi legacy found in Norwegian trees". BBC News Online. Retrieved 2018-04-17.

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