One final group of carboxylic acid derivatives is the anhydrides. In the formation of an anhydride
from two carboxylic acid molecules, one water molecule is removed. Many anhydrides are cyclic,
which may result from the intramolecular dehydration of a dicarboxylic acid. Anhydrides are named
by replacing acid with anhydride in the name of the corresponding carboxylic acid if the anhydride
is formed from only one type of carboxylic acid. If the anhydride is not symmetrical, both carboxylic
acids are named (without the suffix acid) before anhydride is added to the name. Some examples of
anhydrides are shown in Figure 1.13.
Figure 1.13. Naming Anhydrides
Phthalic anhydride and succinic anhydride are given as examples of cyclic anhydrides; their names
need not be memorized.MNEMONIC
Because hydro– is a prefix meaning water and an– is a prefix meaning not or without, we can
remember that anhydrides have had water molecules removed during formation.MCAT Concept Check 1.4:
Before you move on, assess your understanding of the material with these questions.What would be the names of the ester, amide, and anhydride derivatives of pentanoic acid?
Assume that the R group on the ester is –CH 3 and that the amide is unsubstituted.Ester: