Sulphonic acids. Sulphonic acids and their official nomenclature

You sulfonic acids are a class of organic compounds characterized by the functional group below:

R SO₃H
Functional group (sulfonic acid)

"R" stands for any radical derived from a hydrocarbon. Thus, sulfonic acids can be obtained through a reaction between a hydrocarbon and sulfuric acid, in which a hydrogen in the hydrocarbon ends up being replaced by sulfonic acid and also generating water as by-product:

R─H + HO─ SO₃H → R─ SO₃H + H₂O
hydrocarbon sulfuric acid sulfonic acid water

This consideration of the group ─ SO₃H as a replacement for a hydrogen in a hydrocarbon gives rise to the proposed nomenclature for these compounds, which is given by the following rules:

So, we have the examples:

H₃Ç⁶ ─ ⁵CH₂ ─ ⁴CH ³CH ²CH₂─ ¹CH₃ : 4-methylhexane-3-sulfonic acid
│ │
CH₃ ONLY₃H

CH₃ SO₃H: methanesulfonic acid

CH₃ CH₂SO₃H: ethanesulfonic acid

Sulphonic acids are best known for their application in obtaining sparkling wines, which are present in shampoos, detergents and toothpastes. These salts act as surfactants, that is, they act by decreasing surface tension. The generic name for this class of compounds is ‘surfactants’. On teeth, for example, this is important because it allows penetration into cracks and helps to remove debris from the surface of the enamel. The most common sparkling wine used in toothpaste is sodium lauryl sulfate (H

₃C[CH₂]₁₀CH₂OSO₃At).

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Synthetic detergents used as soap substitutes reduce the surface tension of water and then allow oils and fats to emulsify. In Brazil, anionic synthetic detergents usually contain straight-chain sodium alkylbenzene sulphonates:

Another widely used is sodium lauryl sulfonate, which is a salt obtained by the reaction described below, between a sulfonic acid and sodium hydroxide:

Another example of obtaining a compound with detergent properties is sodium dododecanesulfonate, which is obtained by the reaction below, from dodecan-1-ol:

By Jennifer Fogaça
Graduated in Chemistry

Would you like to reference this text in a school or academic work? Look:

FOGAÇA, Jennifer Rocha Vargas. "Sulphonic Acids"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/acidos-sulfonicos.htm. Accessed on June 27, 2021.