Chlorosulfuric acid

Chlorosulfuric acid
IUPAC name	chlorosulfonic acid
Other names	chloridosulfonic acid, sulfuric chlorohydrin
Identifiers
CAS number	7790-94-5 Y
PubChem	24638
UN number	1754
RTECS number	FX5730000
SMILES	ClS(=O)(=O)O
InChI	1/ClHO3S/c1-5(2,3)4/h(H,2,3,4)
InChI key	XTHPWXDJESJLNJ-UHFFFAOYAO
ChemSpider ID	23040
Properties
Molecular formula	HSO3Cl
Molar mass	116.52 g mol−1
Appearance	colorless liquid that fumes in air
Density	1.753 g cm−3
Melting point	−80 °C
Boiling point	151–52 °C (755 mmHg or 100.7 kPa)
Solubility in water	hydrolysis
Solubility in other solvents	reacts with alcohols soluble in chlorocarbons
Refractive index (nD)	1.433
Structure
Molecular shape	tetrahedral
Hazards
MSDS	ICSC 1039
EU Index	016-017-00-1
EU classification	Corrosive (C)
R-phrases	R14, R35, R37
S-phrases	(S2), S26, S45
NFPA 704	0 4 2 W
Related compounds
Related compounds	Sulfuryl chloride Sulfuric acid
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chlorosulfuric acid is HSO₃Cl. This tetrahedral molecule is an intermediate, chemically and conceptually, between SO₂Cl₂ and H₂SO₄. It is also known as chlorosulfonic acid. It is a distilable, colorless liquid that should be handled with care. It is a hygroscopic and a powerful lachrymator.

Synthesis

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

HCl + SO₃ → ClSO₂OH

It can also be prepared by chlorination of sulfuric acid, written here for pedagogical purposes as SO₂(OH)₂, vs. the usual format H₂SO₄:

PCl₅ + SO₂(OH)₂ → ClSO₂OH + POCl₃ + HCl

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

Related compounds

• FSO₂OH is a strong acid and shows only a mild tendency to evolve HF.
• Bromosulfonic acid, BrSO₂OH, is unstable, decomposing at its melting point of 8°C to give Br₂, SO₂, and H₂SO₄.
• Iodosulfonic acid is unknown.

Applications

ClSO₂OH is used to prepare sulfonic acids, which are useful in detergents and as chemical intermediates.

R-H + ClSO₂OH → RSO₂OH + HCl

An early synthesis of saccharin begins with the reaction of toluene with ClSO₂OH to give the ortho- and para-toluene sulfonyl chloride derivatives:

CH₃C₆H₅ + 2ClSO₂OH → CH₃C₆H₄SO₂Cl + H₂SO₄

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

Chlorosulfuric_acid is used in the processing of Carbon nanotubes in which it is employed for dissolving the Carbon nanotubes without chemically modifying them, causing the nano fibers to align prior to spinning or weaving thereby yielding a much stronger and consistent product. ^[1]

Safety considerations

ClSO₂OH reacts violently with water to yield sulfuric acid and HCl. Inhalation of ClSO₂OH would generate HCl in the lungs, which is very dangerous. Thus, precautions associated with HCl should be observed.

References

This article's citation style may be unclear. The references used may be made clearer with a different or consistent style of citation, footnoting, or external linking. (September 2007)

1. ^ Acid solution for nanotube fibres http://www.rsc.org/chemistryworld/News/2009/November/01110902.asp

• Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001, pages 549-550 (discussion of XSO₂OH for X = F, Cl, Br, I)
• R.J. Cremlyn, "Chlorosulfonic Acid" Springer-Verlag New York, Inc. (Royal Society of Chemistry, 2002, 300 pp. ISBN 978-0-85404-498-6