sulfonic acid

Any of several organic acids containing one or more sulfonic groups.

A derivative of sulfuric acid (HOSO₂OH) in which an OH has been replaced by a carbon group, as shown in the structure below.

The aliphatic sulfonic acids are generally made by oxidation of thiols. Several have unique properties. For example, trifluoromethanesulfonic acid, CF₃SO₃H, is such a strong acid that it will protonate sulfuric acid. A compound derived from natural camphor, 10-camphorsulfonic acid, is used extensively in the optical resolution of amines.

Aromatic sulfonic acids are much more important than those of the aliphatic series. Aromatic sulfonic acids are produced by sulfonation of aromatic compounds with sulfuric acid or fuming sulfuric acid. Sulfonation of aromatic hydrocarbons is a reversible process; treatment of an aromatic sulfonic acid with superheated steam removes the SO₃H group. This process can be used in purifying aromatic hydrocarbons. Aromatic sulfonic acids and their derivatives, especially metal salts, are important industrial chemicals. See also Sulfuric acid.

The most extensive use of the sulfonation reaction is in the production of detergents. The most widely used synthetic detergents are sodium salts of straight-chain alkylbenzenesulfonic acids.

Sulfonated polymers, particularly sulfonated polystyrenes, act as ion-exchange resins which have important applications in water softening, ion-exchange chromatography, and metal separation technology. Both sulfonated polymers and simple aromatic sulfonic acids, particularly p-toluenesulfonic acid, are frequently used as acid catalysts in organic reactions such as esterification and hydrolysis. See also Homogeneous catalysis; Ion exchange.

The sulfonic group, in either acid or salt form, is capable of making many substances water soluble, increasing their usefulness. This application is particularly significant in the dying industry, in which a majority of the dyes are complex sodium sulfonates. Many acid-base indicators are soluble due to the presence of a sodium sulfonate moiety. Some pigments used in the paint and ink industry are insoluble metal salts or complexes of sulfonic acid derivatives. Most of the brighteners used in detergents compounded for laundering are sulfonic acid derivatives of heterocyclic compounds. See also Acid-base indicator; Dye; Organosulfur compound.

Sulfonic acid usually refers to a member of the class of organic acids with the general formula R-S(=O)₂-OH, where R is usually a hydrocarbon side chain. The term sulfonic acid may also refer to a particular member of this class, namely the case where R=hydrogen. Sulfonic acids are related to sulfuric acid, with one hydroxyl group removed.

Contents 1 Sulfonic acid (H-S(=O)2-OH) 2 Sulfonic acids (R-S(=O)2-OH) 3 Sulfonic esters 4 Sulfonyl halides 5 See also 6 References

Sulfonic acid (H-S(=O)₂-OH)

Chemical structure of sulfonic acid.

Sulfonic acid is the less stable tautomer of sulfurous acid HO-S(=O)-OH into which sulfonic acid converts rapidly. Derived compounds which replace the sulfur-bonded hydrogen with organic groups are called sulfonic acids and are stable.

Sulfonic acids (R-S(=O)₂-OH)

Ball-and-stick model of methanesulfonic acid

Sulfonic acids are a class of organic acids with the general formula R-S(=O)₂-OH, where R is usually a hydrocarbon side chain. Sulfonic acids are typically much stronger acids than their carboxylic equivalents, and have the unique tendency to bind to proteins and carbohydrates tightly; most "washable" dyes are sulfonic acids (or have the functional sulfonyl group in them) for this reason. They are also used as catalysts and intermediates for a number of different products. Sulfonic acids and their salts (sulfonates) are used extensively in such diverse products like detergents, antibacterial drugs sulfa drugs, anion exchange resins (water purification) and dyes. The simplest example is methanesulfonic acid, CH₃SO₂OH, which is a reagent regularly used in organic chemistry. p-Toluenesulfonic acid is also an important reagent.

Sulfonic esters

Methyl triflate

Sulfonic esters are a class of organic compounds with the general formula R-SO₂-OR. Sulfonic esters such as methyl triflate are considered good leaving groups in nucleophilic aliphatic substitution.

Sulfonyl halides

Main article: sulfonyl halide

Sulfonyl halide groups occur when a sulfonyl functional group is singly bonded to a halogen atom. They have the general formula R-SO2-X where X is a halogen.

See also

• Sulfuric acid H₂SO₄
• Sulfonium S⁺, S⁺R₃

References

• J.A. Titus, R. Haugland, S.O. Sharrow and D.M. Segal , Texas red, a hydrophilic, red-emitting fluorophore for use with fluorescein in dual parameter flow microfluorometric and fluorescence microscopic studies. J. Immunol. Methods 50 (1982), pp. 193–204. doi:10.1016/0022-1759(82)90225-3
• C. Lefevre, H.C. Kang, R.P. Haugland, N. Malekzadeh, S. Arttamangkul, and R. P. Haugland, Texas Red-X and Rhodamine Red-X, New Derivatives of Sulforhodamine 101 and Lissamine Rhodamine B with Improved Labeling and Fluorescence Properties, Bioconj Chem 1996, 7(4):482-9 doi:10.1021/bc960034p

v • d • e Functional groups Chemical class: Alcohol • Aldehyde • Alkane • Alkene • Alkyne • Amide • Amine • Azo compound • Benzene derivative • Carboxylic acid • Cyanate • Disulfide • Ester • Ether • Haloalkane • Hydrazone • Imine • Isocyanide • Isocyanate • Ketone • Oxime • Nitrile • Nitro compound • Nitroso compound • Peroxide • Phosphoric acid • Pyridine derivative • Sulfone • Sulfonic acid • Sulfoxide • Thioester • Thioether • Thiol

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