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 An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the formula HSO₃Cl. It is also known as chlorosulfonic acid, being the

sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

chlorine Chlorine is a chemical element; it has Symbol (chemistry), 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 ...

. It is a distillable, colorless liquid which is

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...

and a powerful lachrymator. Commercial samples usually are pale brown or straw colored.

Salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

and

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s 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 In electromagnetism, the magnetic susceptibility (; denoted , chi) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the applied magnet ...

that chlorine is directly bonded to sulfur. 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. Sulfuryl chloride is commonly confused with thionyl chloride, SOC ...

(SO₂Cl₂) and

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

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

with a

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solu ...

sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3. It has been described as "unquestionably the most conomicallyimportant sulfur oxide". It is prepared on an industrial scale as a precursor to ...

: :HCl + SO₃ → ClSO₃H It can also be prepared by the method originally used by acid's discoverer

Alexander William Williamson Alexander William Williamson Fellow of the Royal Society, FRS FRSE Chemical Society, PCS MRIA (1 May 18246 May 1904) was an English chemist. He is best known today for the Williamson ether synthesis. Life Williamson was born in 1824 in Wands ...

in 1854, 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

Applications

ClSO₂OH is used to prepare alkyl sulfates, which are useful as

detergent A detergent is a surfactant or a mixture of surfactants with Cleanliness, cleansing properties when in Concentration, dilute Solution (chemistry), solutions. There are a large variety of detergents. A common family is the alkylbenzene sulfonate ...

s and as chemical intermediates: :ROH + ClSO₃H → ROSO₃H + HCl One historical synthesis of

saccharin Saccharin, also called saccharine, benzosulfimide, or E954, or used in saccharin sodium or saccharin calcium forms, is a non-nutritive artificial sweetener. Saccharin is a sultam that is about 500 times sweeter than sucrose, but has a bitter or ...

begins with the reaction of

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

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. The benzoyl group is often abbreviated "Bz" (not to be confused with "Bn," which ...

derivative that then is cyclized with

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

and neutralized with base to afford saccharin. Chlorosulfonic acid has been used as an anti-

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

agent in Ryan Model 147 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, which are corrosive: :ClSO₃H + H₂O → H₂SO₄ + HCl

Related halosulfuric acids

Fluorosulfonic acid Fluorosulfuric acid (IUPAC name: sulfurofluoridic acid) is the inorganic compound with the chemical formula . It is one of the strongest acids commercially available. It is a tetrahedral molecule and is closely related to sulfuric acid, , substitu ...

, FSO₂OH, is a related

strong acid Acid strength is the tendency of an acid, symbolised by the chemical formula , to dissociate into a hydron (chemistry), proton, , and an anion, . The Dissociation (chemistry), dissociation or ionization of a strong acid in solution is effectivel ...

with a diminished tendency to evolve

hydrogen fluoride Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...

. * Bromosulfonic acid, BrSO₂OH, is unstable, decomposing at its melting point of 8 °C to give

bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

, and

. *Iodosulfonic acid is not known to occur.

References

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