What Is Chlorosulfonic Acid?
Chlorosulfonic acid is an inorganic compound with the chemical formula HSO3Cl or SO2Cl(OH).
It is also called “sulfuric chloride” or “hydrogen chlorotrioxosulfate. The formula weight is 116.52 g/mol, melting point is -80 °C, density is 1.753 g/cm3, and CAS number is 7790-94-5. At room temperature and pressure, it is a colorless to pale yellow cloudy oily liquid with a strong pungent odor.
Uses of Chlorosulfonic Acid
Chlorosulfonic acid is used as a sulfonating agent in raw materials for synthetic detergents, pharmaceuticals, and dyes. Chlorosulfonic acid has a variety of uses and is consumed in large quantities in Japan.
1. Reactant in Organic Chemistry
Chlorosulfonic acid is mainly used as a reactant in sulfonation reactions. Sulfonation is a reaction in which a hydrogen atom of an organic compound is replaced by a sulfur group. Usually, sulfuric acid, fuming sulfuric acid, or acetyl sulfuric acid is used. Chlorosulfonic acid is particularly useful as a sulfonation reagent for compounds that are difficult to react with.
The reason for this is that the chlorine atom bonded to the sulfur atom is removed as a chloride ion in the sulfonation reaction, and this substitution reaction proceeds quickly because the chloride ion is very stable and excellent as a leaving group.
Another reason is that the use of chlorosulfonic acid is less expensive, and the intense sulfonation reaction using sulfuric acid produces a variety of unnecessary byproducts, which can be suppressed. However, there is a disadvantage in that the reactivity is very high and must be controlled.
The introduction of sulfo groups is very important because many neutral detergents have sulfo groups and quaternary amines at both ends, making them charge-neutral. Many dyes also have sulfo groups in their molecules. Therefore, this sulfonation reaction is an important process in the manufacture of neutral detergents and dyes, and chlorosulfonic acid is a raw material in the manufacture of neutral detergents and dyes.
2. Other
Since chlorosulphonic acid reacts with water to form white smoke of hydrochloric acid and sulfuric acid, it is also used as a raw material for smoke screens used in military settings and is sprayed into the exhaust of stealth bombers to adsorb moisture in the exhaust to suppress the generation of airplane clouds from the exhaust of the bomber’s engine.
Properties of Chlorosulfonic Acid
Chlorosulfonic acid is a highly reactive substance and reacts violently with water and ethanol. When reacting with water in particular, it decomposes to produce sulfuric acid and hydrochloric acid and is highly hygroscopic and fumes in the air.
Therefore, it is important to select a solvent with no nucleophilic properties when dissolving it in a solvent. It is soluble in chloroform, dichloromethane, and pyridine, but insoluble in carbon disulfide and carbon tetrachloride.
Other Information on Chlorosulfonic Acid
1. Synthesis of Chlorosulfonic Acid
Chlorosulfonic acid can be synthesized by reacting phosphorus pentachloride with concentrated sulfuric acid. It can also be synthesized by reacting sulfur trioxide with hydrochloric acid.
2. Hazards of Chlorosulfonic Acid
Chlorosulfonic acid is classified as a deleterious substance under the Poisonous and Deleterious Substances Control Law. It is highly corrosive and causes severe chemical wounds when it comes into contact with the skin, so it should be handled with care. It is highly irritating not only to the skin but also to the eyes, and if ingested can cause severe damage to internal organs.
If it comes into contact with the skin, it is important to immediately wash it off with large amounts of water. If swallowed, immediate medical attention should be sought.
If left in the air, hydrogen chloride and sulfuric acid will react with moisture in the air to form dangerous hydrogen chloride and sulfuric acid, respectively. When handling, it is essential to wear a lab coat, protective clothing, rubber gloves, and safety glasses.