Organic anhydrides are compounds derived from dehydration reactions of carboxylic acids. Hence the origin of its name, as anhydros, in Greek, means "no water".
Thus, in the anhydride formation reaction, two molecules of a carboxylic acid react to form an anhydride molecule. Below is an example of the formation of the most important anhydride, acetic anhydride or ethanoic anhydride:
Acetic anhydride formation reaction.
Thus, the characteristic functional group of anhydrides is:
Functional group of anhydrides.
There are normal or symmetrical anhydrides, which are like acetic anhydride, and are so named because their radicals are the same. If the radicals are different, we say the anhydride is mixed. Also, there are cyclic anhydrides.
The official nomenclature of anhydrides, according to IUPAC (International Union of Pure Chemistry and Applied), is made based on the acid from which it was formed, that is, the word "acid" is replaced by "anhydride". For example, in the case shown above, the source acid was ethanoic acid or acetic acid, thus the resulting anhydride was ethanoic anhydride or acetic anhydride.
The structure of this nomenclature is as follows:
Official nomenclature of anhydrides.
Look at the examples:
As already mentioned, acetic anhydride is very important, as it is used to obtain acetylsalicylic acid (ASA), commonly known as aspirin and used as an antipyretic.
Examples of naming some anhydrides.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/anidridos-organicos.htm
