Carboxylic acids were among the earliest organic compounds studied by chemists. The Swedish pharmaceutical chemist C.W. Scheele was the first to discover many carboxylic acids at the end of the 18th century, well before the theory of the chemical structure had been developed.
Not only carboxylic acids themselves but also their functional derivatives are of chemical and biochemical interest.
Carboxylic acids are compounds of the general formula RCOOH that have the carboxyl group -COOH as a functional group. Acid derivatives have the general formula RC(O)Z, where Z is a substituent containing an unshared electron pair.
The most important acid derivatives are esters, amides, anhydrides, thioesters, and acid halides. Acid derivatives are called so because all of them can be derived from carboxylic acids and can be hydrolyzed to regenerate carboxylic acids.
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9.1. GENERAL CHARACTERISTICS OF CARBOXYLIC ACIDS
Carboxylic acids and their numerous derivatives form a family of compounds whose chemistry is exclusively varied. It is no wonder because we observe various types of functions in their molecules.
9.1.1. Classification and Nomenclature
Carboxylic acids may be classified similarly to aldehydes (Sec. 8.1.1), i. e. as aliphatic or aromatic ones. The classification signs may be extended with unsaturated, heterocyclic, and dicarboxylic acids. These types are exemplified below and presented in Table 9.1.
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Table 9.1. Names and some physical constants of selected carboxylic acids
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* The word acid is omitted in the table.
** For dicarboxylic acids the first number denotes pKa1, the second one - pKa2. *** Melts or boils with decomposition.
For historical reasons mentioned above, many carboxylic acids received their trivial names long ago. Many of them (and all the names listed in Table 9.1) are allowed, and even recommended by the IUPAC rules, including the names of acid derivatives (Table 9.2). Trivial names are preferably used in the biochemical literature.