sulfonic acid

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sulfonic acid

(səlfŏn`ĭk), organic compound containing the functional groupfunctional group,
in organic chemistry, group of atoms within a molecule that is responsible for certain properties of the molecule and reactions in which it takes part. Organic compounds are frequently classified according to the functional group or groups they contain.
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 RSO2OH, which consists of a sulfur atom, S, bonded to a carbon atom that may be part of a large aliphatic or aromatic hydrocarbonhydrocarbon
, any organic compound composed solely of the elements hydrogen and carbon. The hydrocarbons differ both in the total number of carbon and hydrogen atoms in their molecules and in the proportion of hydrogen to carbon.
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, R, and also bonded to three oxygen atoms, O, one of which has a hydrogen atom, H, attached to it. The hydrogen atom makes the compound acidic, much as the hydrogen of a carboxylic acid (see carboxyl groupcarboxyl group
, in chemistry, functional group that consists of a carbon atom joined to an oxygen atom by a double bond and to a hydroxyl group, OH, by a single bond. Carboxylic acids are compounds whose molecules contain a carboxyl group that is joined to a hydrogen atom, an
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) makes it acidic (see acids and basesacids and bases,
two related classes of chemicals; the members of each class have a number of common properties when dissolved in a solvent, usually water. Properties
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). However, while carboxylic acids are weak (with dissociation constants of about 10−5), sulfonic acids are considered strong acids (with dissociation constants of about 10−2). Because sulfonic acids are so acidic, they generally exist as their saltssalt,
chemical compound (other than water) formed by a chemical reaction between an acid and a base (see acids and bases). Characteristics and Classification of Salts

The most familiar salt is sodium chloride, the principal component of common table salt.
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 and thus tend to be quite soluble in water. Sulfonic acid groups are often introduced into organic molecules such as dyes to stabilize them for use in aqueous dye baths. Sulfonic acid groups also improve the washfastness of wool and silk dyes by enabling the dye to bind more tightly to the fabric. The most important use of sulfonic acid salts (sulfonates) is in the detergent industry. Sodium salts of long-chain aliphatic or aromatic sulfonic acids are used as detergents. Unlike ordinary soapssoap,
a cleansing agent. It cleanses by lowering the surface tension of water, by emulsifying grease, and by absorbing dirt into the foam.

Ancient peoples are believed to have employed wood ashes and water for washing and to have relieved the resulting irritation with
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, which contain carboxylic acid salts, soaps containing sulfonates do not form a scum in hard water because the calcium and magnesium ions present in the hard water do not form insoluble precipitates with sulfonates as they do with carboxylates. Some sulfonic acid derivatives, e.g., the sulfa drugs, are important as antibiotics.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Sulfonic Acid


any of several acids of the general formula RSO3H, where R is an aliphatic or aromatic hydrocarbon radical. Sulfonic acids are usually hygroscopic, crystalline substances that dissolve readily in water. Their acidity is close to that of mineral acids.

Aromatic sulfonic acids are obtained by sulfonation of aromatic hydrocarbons and their derivatives. Aliphatic sulfonic acids are prepared by sulfochlorination of hydrocarbons or by replacement of the halogen with the sulfonic acid group, —SO3H (see).

Under the action of PC15, sulfonic acids are converted to sulfo-nyl chlorides, RSO2C1. Reduction of sulfonic acids produces sulfinic acids, RSO2H, and mercaptans, RSH. The SÓ3H group in the aromatic ring is easily replaced by H, OH, OR, H2N, R2N, and other groups under the action of nucleophilic reagents.

Aromatic sulfonic acids are important intermediates in industrial organic synthesis, such as the production of phenols. They are used in the production of azo dyes, sulfa drugs, ion-exchange resins, and additives for electroplating baths. The basic and quaternary ammonium salts of aliphatic sulfonic acids, called sulfonates, are surfactants and are used as components of detergents.

In inorganic chemistry, the term “sulfonic acid” is sometimes used in reference to thio acids.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

sulfonic acid

[¦səl¦fän·ik ′as·əd]
(organic chemistry)
A compound with the radical ‒SO2OH, derived by the sulfuric acid replacement of a hydrogen atom; for example, conversion of benzene, C6H6, to the water-soluble benzenesulfonic acid, C6H5SO3H, by treatment with sulfuric acid; used to make dyes and drugs.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.