Acid anhydrides
Acylating agents that connect carboxylic-acid chemistry to esters and amides.
- Functional group
- C(=O)-O-C(=O)
- Also known as
- acid anhydride, carboxylic acid anhydrides, carboxylic anhydrides
Overview
Acylating agents that connect carboxylic-acid chemistry to esters and amides.
Acid anhydrides contain two acyl groups joined through oxygen. They transfer an acyl group to alcohols or amines and hydrolyse to carboxylic acids. Ethanoic anhydride connects acylation with aspirin chemistry; mixed and cyclic anhydrides require attention to which acyl group reacts.
Identifiers
- Functional group
- C(=O)-O-C(=O)
- Also known as
- acid anhydride, carboxylic acid anhydrides, carboxylic anhydrides
Properties
- Acylation by-product
- A carboxylic acid or carboxylate accompanies acyl transfer, rather than the HCl formed from an acyl chloride.
- Relative reactivity
- Usually less reactive than acyl chlorides; still reactive enough for ester and amide preparation.
Related compounds
- Acetic anhydride
Acetic anhydride is a specific member of the acid anhydrides family.
- Maleic anhydride
Maleic anhydride is a specific member of the acid anhydrides family.
Connected reactions
- Anhydride hydrolysis: Acid anhydrides → Carboxylic acids
Water attacks an anhydride carbonyl, and collapse of the tetrahedral intermediate breaks the acyl-oxygen linkage. Proton transfer gives carboxylic-acid products; a mixed anhydride yields two different acids.
- Anhydride alcoholysis: Acid anhydrides → Esters
Alcohol oxygen attacks an anhydride carbonyl and the tetrahedral intermediate expels carboxylate. Proton transfer produces the ester and a carboxylic acid; one acyl fragment transfers to the alcohol.
- Anhydride ammonolysis: Acid anhydrides → Amides
Ammonia attacks the anhydride carbonyl to form a tetrahedral intermediate. Carboxylate departure and proton transfer give an amide; excess ammonia also converts the acid co-product into ammonium carboxylate.
References
- Organic Chemistry: Chemistry of Acid AnhydridesJohn McMurry · OpenStax Organic Chemistry · 2023
Supports functional-group chemistry used to curate the linked examples. Checked 2026-09-16; named examples are applications of textbook scope, without claimed experimental yields.
- PubChem Compound Summary: Acetic anhydride (CID 7918)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.
- PubChem Compound Summary: Maleic anhydride (CID 7923)National Center for Biotechnology Information · PubChem
Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.