Benzenesulfonic acid
Encyclopedia
Benzenesulfonic acid is an organosulfur compound with the formula C6H5SO3H. It is the simplest aromatic
sulfonic acid
. It forms colorless deliquescent sheet crystals or a white waxy solid that is soluble in water and ethanol, slightly soluble in benzene
and insoluble in carbon disulfide
and diethyl ether
. It is often stored in the form of alkali metal salts. Its aqueous solution is strongly acidic
.
of benzene
using concentrated sulfuric acid
:
This conversion illustrates aromatic sulfonation, which has been called "one of the most important reactions in industrial organic chemistry."
s, forming sulfonamides, sulfonyl chloride, and esters. The sulfonation is reversed above 220 °C. Dehydration with phosphorus pentoxide
gives benzenesulfonic acid anhydride ((C6H5SO2)2O). Conversion to the corresponding benzenesulfonyl chloride (C6H5SO2Cl) is effected with phosphorus pentachloride.
It is a strong acid, being dissociated in water.
:
The process has been largely displaced by the Hock process, which generates less waste.
Benzenesulfonic acid is mainly consumed by conversion to other specialty chemicals. A variety of pharmaceutical drugs are prepared as salts of benzenesulfonic acid and are known as besylates or besilates.
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...
sulfonic acid
Sulfonic acid
Sulfonic acid usually refers to a member of the class of organosulfur compounds with the general formula RS2–OH, where R is an alkyl or aryl. The formal part of acid, HS2–OH, are formally derivatives of the "parent" inorganic compound with the formula HSO2.-Preparation:Sulfonic acid is...
. It forms colorless deliquescent sheet crystals or a white waxy solid that is soluble in water and ethanol, slightly soluble in benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
and insoluble in carbon disulfide
Carbon disulfide
Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...
and diethyl ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...
. It is often stored in the form of alkali metal salts. Its aqueous solution is strongly acidic
Strong acid
A strong acid is an acid that ionizes completely in an aqueous solution by losing one proton, according to the equationFor sulfuric acid which is diprotic, the "strong acid" designation refers only to dissociation of the first protonMore precisely, the acid must be stronger in aqueous solution than...
.
Preparation
Benzenesulfonic acid is prepared from the sulfonationAromatic sulfonation
Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution.-Mechanism:...
of benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
using concentrated sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
:
This conversion illustrates aromatic sulfonation, which has been called "one of the most important reactions in industrial organic chemistry."
Reactions
Benzenesulfonic acid exhibits the reactions typical of other aromatic sulfonic acidSulfonic acid
Sulfonic acid usually refers to a member of the class of organosulfur compounds with the general formula RS2–OH, where R is an alkyl or aryl. The formal part of acid, HS2–OH, are formally derivatives of the "parent" inorganic compound with the formula HSO2.-Preparation:Sulfonic acid is...
s, forming sulfonamides, sulfonyl chloride, and esters. The sulfonation is reversed above 220 °C. Dehydration with phosphorus pentoxide
Phosphorus pentoxide
Phosphorus pentoxide is a chemical compound with molecular formula P4O10 . This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant.-Structure:...
gives benzenesulfonic acid anhydride ((C6H5SO2)2O). Conversion to the corresponding benzenesulfonyl chloride (C6H5SO2Cl) is effected with phosphorus pentachloride.
It is a strong acid, being dissociated in water.
Applications
The alkali metal salt of benzenesulfonic acid was once widely used in the production of phenolPhenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
:
- C6H5SO3Na + 2 NaOH → C6H5ONa + Na2SO3
- C6H5ONa + 2 HCl → C6H5OH + NaCl
The process has been largely displaced by the Hock process, which generates less waste.
Benzenesulfonic acid is mainly consumed by conversion to other specialty chemicals. A variety of pharmaceutical drugs are prepared as salts of benzenesulfonic acid and are known as besylates or besilates.