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GENERAL
This sub-Chapter covers the carboxylic acids which contain the characteristic function (-COOH), called the carboxyl group. In theory, the heading also covers the ortho-acids (RC(OH)3) since these may be regarded as hydrated carboxylic acids (RCOOH + H2O = RC(OH)3). In practice, however, these do not exist in the free state, but they do give rise to stable esters (ortho-esters, to be regarded as esters of hydrated carboxylic acids).
Carboxylic acids may contain one or more carboxyl groups (-COOH) (monocarboxylic acids or polycarboxylic acids, respectively).
If the hydroxyl group (-OH) is removed, the residue is an acyl radical which can be representedby the formula (RCO-) where R is an alkyl or aryl radical (methyl, ethyl, phenyl, etc.). Acyl radicals enter into the formulae of anhydrides, halides, peroxides, peroxyacids, esters and salts.
Sulphonic acids, which contain the group (-SO3H) are quite different from carboxylic acids; they are classified as sulphonated derivatives in various sub-Chapters. This sub-Chapter includes only those which are sulphonated derivatives of the chemicals of this sub-Chapter.(A) ACID ANHYDRIDES
Acid anhydrides result from the elimination of a molecule of water, either from two molecules of a monobasic acid, or from one molecule of dibasic acid. They are characterised by the group (-C(O)OC(O)-). (B) ACID HALIDES
The halides (e.g., chlorides and bromides) of acids have the general formula (RCOX, where X is a halogen), i.e., they are represented by acyl radicals combined with chlorine, bromine or other halogens. (C) ACID PEROXIDES
Acid peroxides are compounds in which two acyl radicals are linked by two oxygen atoms; their general formula is (RC(O)OOC(O)R). (D) PEROXYACIDS
Peroxyacids have the general formula (RC(O)OOH). (E) ESTERS OF ACIDS
Esters of carboxylic acids are obtained by replacing the hydrogen atom of the carboxyl group (-COOH) by an alkyl or aryl radical. They may be represented by the general formula (RC(O)OR1) in which R and R1 are alkyl or aryl radicals (methyl, ethyl, phenyl, etc.). (F) SALTS OF ACIDS
Salts of carboxylic acids are obtained by replacing the hydrogen atom of the carboxyl group (-COOH) by an inorganic cation, for example, sodium, potassium, ammonium. They may be represented by the formula (RC(O)OM) in which R is an alkyl, aryl or alkaryl radical and M is a metallic or other inorganic cation. (G) HALOGENATED, SULPHONATED, NITRATED OR NITROSATED DERIVATIVES OF ACIDS
In the halogenated, sulphonated, nitrated or nitrosated derivatives of the compounds described in Parts (A) to (F) above, the oxygen-containing functional groups remain intact, but one or more hydrogens in the radicals R or R1 have been replaced, respectively, by halogens, sulpho (-SO3H), nitro (-NO2) or nitroso (-NO) groups or by any combination thereof.
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