The acid anhydrides are considered of great importance from the wide variety of compounds of organic origin in the world. These are presented as molecules that have two acyl groups (organic substituents whose formula is RCO-, where R is a carbon chain) attached to the same oxygen atom.
Also, there is a class of acid anhydrides that is commonly found: carboxylic anhydrides, so named because the starting acid is a carboxylic acid. To name those of this type whose structure is symmetric, only a substitution of terms must be made.
The term acid in the nomenclature of its original carboxylic acid should be replaced by the term anhydride, which means "without water", without altering the rest of the name of the molecule formed. These compounds can also be generated starting from one or two acyl groups from other organic acids, such as phosphonic acid or sulfonic acid.
Similarly, acid anhydrides can be produced based on an inorganic acid, such as phosphoric acid. However, its physical and chemical properties, its applications and other characteristics depend on the synthesis carried out and the structure of the anhydride.
How are acid anhydrides formed?
The general formula for acid anhydrides is (RC (O)) 2 O, which is best seen in the image placed at the beginning of this article.
For example, for acetic anhydride (from acetic acid) the general formula is (CH 3 CO) 2 O, being written similarly for many other similar acid anhydrides.
As previously mentioned, these compounds have almost the same name as their precursor acids, and the only thing that changes is the term acid for anhydride, since the same rules for numbering atoms and substituents must be followed to get their nomenclature right.
Applications
Acid anhydrides have many functions or applications depending on the field being studied, since, as they have high reactivity, they can be reactive precursors or form part of many important reactions.
An example of this is industry, where acetic anhydride is produced in large quantities because it has the simplest structure that can be isolated. This anhydride is used as a reagent in important organic syntheses, such as acetate esters.
Industrial use
On the other hand, maleic anhydride has a cyclic structure, being used in the production of coatings for industrial use and as a precursor of some resins through the copolymerization process with styrene molecules. Furthermore, this substance functions as a dienophile when the Diels-Alder reaction is carried out.
Similarly, there are compounds that have two molecules of acid anhydrides in their structure, such as ethylenetetracarboxylic dianhydride or benzoquinonetetracarboxylic dianhydride, which are used in the synthesis of certain compounds such as polyimides or some polyamides and polyesters.
In addition to these, there is a mixed anhydride called 3′-phosphoadenosine-5′-phosphosulfate, from phosphoric and sulfuric acids, which is the most common coenzyme in biological sulfate transfer reactions.
Examples of acid anhydrides
- Wikipedia. (2017). Wikipedia. Recovered from en.wikipedia.org
- Johnson, AW (1999). Invitation to Organic Chemistry. Recovered from books.google.co.ve.
- Acton, QA (2011). Acid Anhydride Hydrolases: Advances in Research and Application. Recovered from books.google.co.ve
- Bruckner, R., and Harmata, M. (2010). Organic Mechanisms: Reactions, Stereochemistry and Synthesis. Recovered from books.google.co.ve
- Kim, JH, Gibb, HJ, and Iannucci, A. (2009). Cyclic Acid Anhydrides: Human Health Aspects. Recovered from books.google.co.ve