Nomenclature of Carboxylic Acid Derivatives: Acid Halides, Esters, and Acid Anhydrides

Naming Acid Halides

The IUPAC and common names of acid halides are derived from the corresponding carboxylic acids, by changing “ic acid” to “yl halide.” For example, as shown below, the IUPAC name ethanoyl chloride is derived from ethanoic acid, and the common name, acetyl chloride, is obtained from acetic acid.

IUPAC:	Ethanoic acid	Ethanoyl chloride
Common:	Acetic acid	Acetyl chloride

Cyclic acid halides are named by replacing the suffix “carboxylic acid” with “carbonyl halide.” For instance, if the acetyl chloride group is bonded to a cyclohexane ring, the resulting compound is called cyclohexanecarbonyl chloride, derived from the parent cyclohexanecarboxylic acid.

IUPAC:	Cyclohexanecarboxylic acid	Cyclohexanecarbonyl chloride
Common:	Cyclohexanecarboxylic acid	Cyclohexanecarbonyl chloride

Naming Esters

Esters are named by citing the alkyl group attached to the oxygen atom first, and then adding the name of the acid, where the suffix “ic acid” is substituted with “ate.” In this example, the IUPAC name of the ester is methyl ethanoate derived from ethanoic acid, and the common name, methyl acetate, is obtained from acetic acid.

IUPAC:	Ethanoic acid	Methyl ethanoate
Common:	Acetic acid	Methyl acetate

Cyclic esters, also referred to as lactones, are named by replacing the suffix “ic acid” of the parent acid with “olactone.” The following example is that of a cyclic four-membered ester where the IUPAC and common names are butanolactone and butyrolactone, respectively.

For IUPAC names, the location of the oxygen atom on the ring is deduced by numbering the carbons starting from the carbonyl carbon, and adding it as a prefix. Thus, butanolactone becomes 4-butanolactone. In common names, the number is replaced by a Greek letter; however, the carbon atom adjacent to the carbonyl carbon is labelled first, giving the name γ-⁠butyrolactone.

IUPAC:	Butanoic acid	4-Butanolactone
Common:	Butyric acid	γ-Butyrolactone

Naming Acid Anhydrides

Acid anhydrides can be symmetrical or unsymmetrical. Symmetrical anhydrides are formed from a mixture of two identical carboxylic acids and are named by changing the suffix “acid” with “anhydride”. For example, the IUPAC name ethanoic anhydride is derived from ethanoic acid, and the common name, acetic anhydride, is obtained from acetic acid.

IUPAC:	Ethanoic acid	Ethanoic anhydride
Common:	Acetic acid	Acetic anhydride

In contrast, unsymmetrical anhydrides are formed from a mixture of two different acids and are named by citing both acids in alphabetical order, followed by the suffix “anhydride.” In the following example, the IUPAC and common names are ethanoic propanoic anhydride and acetic propionic anhydride, respectively.

IUPAC:	Ethanoic acid	Propanoic acid	Ethanoic propanoic anhydride
Common:	Acetic acid	Propionic acid	Acetic propionic anhydride

Unlike acyclic acid anhydrides, cyclic anhydrides are synthesized from dicarboxylic acids. However, the nomenclature follows the same rules, and the compounds are named by replacing the suffix “acid” with “anhydride.” As shown below, the IUPAC name butanedioic anhydride is derived from butanedioic acid, and the common name, succinic anhydride, is obtained from succinic acid.

IUPAC:	Butanedioic acid	Butanedioic anhydride
Common:	Succinic acid	Succinic anhydride