General structure of sulfonic acid. R can also be equal to H.

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 oxygen removed.

[edit] 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 that replace the sulfur-bonded hydrogen with organic groups are called sulfonic acids and are stable.

[edit] 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.

[edit] 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.

[edit] Sulfonyl halides

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.

[edit] See also

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

[edit] 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