Chlorosulfuric acid (

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

name: sulfurochloridic acid) is the inorganic compound with the formula HSO₃Cl. It is also known as chlorosulfonic acid, being the sulfonic acid of

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

. It is a distillable, colorless liquid which is

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substan ...

and a powerful

lachrymator Tear gas, also known as a lachrymator agent or lachrymator (), sometimes colloquially known as "mace" after the early commercial aerosol, is a chemical weapon that stimulates the nerves of the lacrimal gland in the eye to produce tears. In ad ...

. Commercial samples usually are pale brown or straw colored.

Salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...

and

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...

s of chlorosulfuric acid are known as chlorosulfates.

Structure and properties

Chlorosulfuric acid is a tetrahedral molecule. The formula is more descriptively written SO₂(OH)Cl, but HSO₃Cl is traditional. It is an intermediate, chemically and conceptually, between

sulfuryl chloride Sulfuryl chloride is an inorganic compound with the formula SO2Cl2. At room temperature, it is a colorless liquid with a pungent odor. Sulfuryl chloride is not found in nature, as can be inferred from its rapid hydrolysis. Sulfuryl chloride is ...

(SO₂Cl₂) and sulfuric acid (H₂SO₄). The compound is rarely obtained pure. Upon standing with excess sulfur trioxide, it decomposes to pyrosulfuryl chlorides: :2 ClSO₃H + SO₃ → H₂SO₄ + S₂O₅Cl₂

Synthesis

The industrial synthesis entails the reaction of

hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...

with a solution of sulfur trioxide in sulfuric acid: :HCl + SO₃ → ClSO₃H It can also be prepared by 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.

Applications

ClSO₂OH is used to prepare alkyl sulfates, which are useful as detergents and as chemical intermediates: :ROH + ClSO₃H → ROSO₃H + HCl An early synthesis of

saccharin Saccharin (''aka'' saccharine, Sodium sacchari) is an artificial sweetener with effectively no nutritional value. It is about 550 times as sweet as sucrose but has a bitter or metallic aftertaste, especially at high concentrations. Saccharin is ...

begins with the reaction of

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) a ...

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 Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, ...

derivative that then is cyclized with

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

and neutralized with base to afford saccharin. Reaction with

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

is used to produce

peroxydisulfuric acid Peroxydisulfuric acid is an inorganic compound with a chemical formula . Also called Marshall's acid after Professor Hugh Marshall, who discovered it in 1891. Structure and bonding This oxoacid features sulfur in its +6 oxidation state and a ...

("persulfuric acid") and

peroxydisulfate The peroxydisulfate ion, , is an oxyanion, the anion of peroxydisulfuric acid. It is commonly referred to as persulfate, but this term also refers to the peroxomonosulfate ion, . It is also called ''peroxodisulfate''. Approximately 500,000 tons o ...

s. These are used as oxidizing agents and for initiating

free radical polymerization In polymer chemistry, free-radical polymerization (FRP) is a method of polymerization by which a polymer forms by the successive addition of free-radical building blocks ( repeat units). Free radicals can be formed by a number of different mechani ...

, for example to produce polytetrafluoroethylene (Teflon). Chlorosulfonic acid has been used as an anti-

contrail Contrails (; short for "condensation trails") or vapor trails are line-shaped clouds produced by aircraft engine exhaust or changes in air pressure, typically at aircraft cruising altitudes several miles above the Earth's surface. Contrails ar ...

agent in

Ryan Model 147 The Ryan Model 147 Lightning Bug is a jet-powered drone, or unmanned aerial vehicle, produced and developed by Ryan Aeronautical from the earlier Ryan Firebee target drone series. Beginning in 1962, the Model 147 was introduced as a reconnais ...

reconnaissance drones, and to produce

smoke screen A smoke screen is smoke released to mask the movement or location of military units such as infantry, tanks, aircraft, or ships. Smoke screens are commonly deployed either by a canister (such as a grenade) or generated by a vehicle (such as ...

Safety

ClSO₃H reacts violently with water to yield sulfuric acid and hydrogen chloride, commonly seen as vapors fuming from the liquid: :ClSO₃H + H₂O → H₂SO₄ + HCl Precautions, such as proper ventilation, associated with HCl should be observed.

Related halosulfuric acids

* Fluorosulfonic acid, FSO₂OH, is a related

strong acid Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H+, and an anion, A-. The dissociation of a strong acid in solution is effectively complete, except in its most concentrated solutions ...

with a diminished tendency to evolve hydrogen fluoride. * Bromosulfonic acid, BrSO₂OH, is unstable, decomposing at its melting point of 8 °C to give

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...

, sulfur dioxide, and sulfuric acid. *Iodosulfonic acid is not known to occur.

References

{{DEFAULTSORT:Chlorosulfuric Acid Oxohalides Reagents for organic chemistry Sulfur oxoacids Sulfuryl compounds Lachrymatory agents