Benzenesulfonic acid

Benzenesulfonic acid^[1]

Names
Other names Benzene sulphonic acid; Benzenesulphonic acid; Phenylsulfonic acid; Phenylsuphonic acid
Identifiers
CAS Number	98-11-3
ChemSpider	7093
Jmol 3D model	Interactive image
UNII	685928Z18A
InChI InChI=1S/C6H6O3S/c7-10(8,9)6-4-2-1-3-5-6/h1-5H,(H,7,8,9) Key: SRSXLGNVWSONIS-UHFFFAOYSA-N InChI=1/C6H6O3S/c7-10(8,9)6-4-2-1-3-5-6/h1-5H,(H,7,8,9) Key: SRSXLGNVWSONIS-UHFFFAOYAJ
SMILES c1ccc(cc1)S(=O)(=O)O
Properties
Chemical formula	C6H6O3S
Molar mass	158.17 g·mol^−1
Appearance	Colorless crystalline solid
Density	1.32 g/cm^3 (47 °C)
Melting point	* 44 °C (hydrate) 51 °C (anhydrous)
Boiling point	190 °C (374 °F; 463 K)
Solubility in water	Soluble
Solubility in other solvents	Soluble in alcohol, insoluble in non-polar solvents
Acidity (pKa)	−2.8[2]
Hazards
Main hazards	Corrosive
Safety data sheet	External MSDS
R-phrases	R20 R22 R34 R36 R37 R38
S-phrases	S26 S36/37/39 S45
Flash point	> 113 °C
Related compounds
Related sulfonic acids	Sulfanilic acid p-Toluenesulfonic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Benzenesulfonic acid is an organosulfur compound with the formula C₆H₅SO₃H. It is the simplest aromatic sulfonic acid. It forms white deliquescent sheet crystals or a white waxy solid that is soluble in water and ethanol, slightly soluble in benzene and insoluble in nonpolar solvents like diethyl ether. It is often stored in the form of alkali metal salts. Its aqueous solution is strongly acidic.

Preparation

Benzenesulfonic acid is prepared from the sulfonation 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."^[3]

Reactions

Benzenesulfonic acid exhibits the reactions typical of other aromatic sulfonic acids, 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.

Applications

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.

The alkali metal salt of benzenesulfonic acid was once widely used in the production of phenol:

C₆H₅SO₃Na + 2 NaOH → C₆H₅ONa + Na₂SO₃

C₆H₅ONa + HCl → C₆H₅OH + NaCl

The process has been largely displaced by the Hock process, which generates less waste.

References

1. Benzenesulfonic acid, Sigma-Aldrich
2. Guthrie, J. P. Hydrolysis of esters of oxy acids: pK_a values for strong acids Can. J. Chem. 1978, 56, 2342-2354. doi:10.1139/v78-385
3. Otto Lindner, Lars Rodefeld "Benzenesulfonic Acids and Their Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a03_507