What are anhydrides?


Although for many, chemistry is simply a difficult subject, which the vast majority only take when they are in high school , it is found in our daily lives in many ways such as anhydrides .


What are anhydrides?

In chemistry we can define anhydrides as chemical compounds  of binary type that arise teeing a nonmetal with oxygen , are also called as oxides No Metallic or Oxides acids , of general formula (RCO) 2 °. And they are products of the condensation of 2 molecules of carboxylic acids

  • Definition
  • Types of anhydrides
  • Characteristics of anhydrides
  • Physical and chemical properties
  • Obtaining
  • Uses and applications
  • Formulation of anhydrides
  • Anhydride nomenclatures


Looking for its etymological origin the word anhydride its origin comes from the Greek is a word that was formed with the sum of several complements: It has the prefix ‘An’ that refers to the equivalent “SIN” , then it has the noun ‘Hydros’ which is synonymous of WATER , and has a suffix ‘gone’ which could mean “THAT HAS ASPECTO”   and giving meaning to the Spanish word is defined as “It looks like it does not have water.”

Types of anhydrides

Symmetric or Simple Anhydrides: That is when condensation occurs and the acids that form it are the same . They are named by replacing the word acid with Anhydride.

Asymmetric or Mixed Anhydrides: They appear when the condensation that occurs is with 2 different acids, and these anhydrides are named alphabetically ordering the acids

Cyclic Anhydrides: They are formed when condensation or cyclization occurs from a diacid , they are named by changing the word Acid and Anhydride is placed and with the ending “oico”. Example: Benzoic Anhydride

Characteristics of anhydrides

Among its features is:

  • The formula of anhydrides is of the type  2 O n  (where X is a non-metallic element and O is oxygen) Examples: SeO, So 3 , CO 2
  • They have the characteristic of being especially reactive .
  • They can be handled in many areas, the usual, where they are most seen and used is in the manufacture of drugs . For example, in the medical field there is a widely used one called Acetylsalicylic Acid, a drug that is widely used
  • As already mentioned, they are the result of the dehydration of two molecules but there are also cases where it could be one, in the intramolecular case, of carboxylic acid.
  • They are also called carboxylic anhydrides .

Physical and chemical properties


They do not have brightness and have different colors , most are substances that form  acid solutions , in their outer layers we find at least 4 electrons although there may be more, in aqueous solution they form Anions or Oxyanions, they do not serve to be conductors of electricity or heat, those that are solid are generally brittle, hard, and others soft.


Once water joins with the two acids that had transformed it into anhydride, they disappear when there is an increase in temperature. This step is called Hydrolysis , when they react with alcohols and phenols, esters are formed Alcoholysis Process) and when they react with ammonia then the famous amides arise (Ammonolysis Process).


Anhydrides are compounds that are obtained at low melting points when they are reacted with non-metal and oxygen, many of the substances that are obtained with the union of both elements are substances in a gaseous form.

When acidic oxides are obtained, they are recognized because they change in color and it is an indicator of acid, for example: blue litmus paper, as this paper is exposed to acid solutions, they turn pink when they come into contact with them.

Uses and applications

Non-metallic anhydrides or oxides have multiple uses and applications in everyday life, only they are used with vulgar names that are constantly in our environment but because we do not know their scientific names, we cannot recognize them, for example:

  • The carbon dioxide , which is largely known as Carbon Dioxide the CO 2 ,  is a gas that has a lot of properties that make it ideal for extinguishing any fire .
  • The sulfur dioxide is used as a preservative and antioxidant which is found in nuts that like to consume us jams,   juice drinks and wine . SO 2
  • The silicic anhydride SiO 2 , handled and used as an abrasive for carrying discs , making sanding and even blocks .
  • The boric anhydride B 2 O 3 , is used in medicine , to create insecticides , in nuclear power is, for preservation, pyrotechnics, among others.
  • The anhydride bromic Br 2 O 5 , bromides obviously involved in medicine as sedatives , specifically silver bromide is handled as a key device for photographic plates to you when you create a bone fractures.
  • The anhydride ethanoic or acetic , is related to the manufacture of cellulose acetate , of resins , also in the synthesis of aspirin, among others.

Formulation of anhydrides

They are stated as follows:

Symbol element is located Nonmetallic by the valence of oxygen sign + and to the side the oxygen with the valence of the metallic element not.

Anhydride nomenclatures

Traditional nomenclature : In anhydrides it is applied as follows, the word Anhydride is placed first and then the name of the Non-Metallic element and it is required to know and be clear about the valence of the non-metal according to these criteria

  • A valence   Ending “ico”
  • Two valences   Termination “bear” lower valence and higher ” ico”
  • Three valences   Ending “Hipo..oso” (in 1), “bear” (in 2), “ico” (in 3).
  • Four valences   Ending “Per..ico” (in the 4)

Stock nomenclature

The word Oxide is placed first, followed by the Nonmetallic element and lastly the valence number of the nonmetal in Roman numerals and in parentheses. Example: Carbon (IV) oxide

Systematic nomenclature

It consists of placing a prefix to the expression Oxide but depending on the number of atoms of each element and then placing the Non-Metallic element preceded by the valence of the non-metal.

According to the atoms they are:

  • GAVE.
  • TRI.
  • TETRA.
  • PENTA.
  • HEXA.
  • HEPTA.

Example: 2 0 5 Diphosphorous Pentaoxide ; Cl 2 O Dichloro Monoxide

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