What does anhydride mean?
An anhydride is a chemical compound formed when water is removed from another compound, most commonly from an acid. The term appears throughout chemistry, where anhydrides are prized for their reactivity: many react readily with water to regenerate the parent acid. In organic chemistry, carboxylic acid anhydrides such as acetic anhydride and phthalic anhydride are important industrial reagents used to make pharmaceuticals, plastics, dyes, and resins. In inorganic chemistry, the word can also describe nonmetal oxides — carbon dioxide, for instance, is the anhydride of carbonic acid — that form acids on contact with water. The name comes from the Greek-derived prefix 'an-' (without) combined with 'hydor' (water), literally meaning 'without water.' Because anhydrides are defined by what they lack rather than what they contain, the word carries a precise, technical character and is essentially confined to scientific writing, laboratory practice, and industrial settings rather than everyday conversation.
nounA chemical compound formed by the removal of water from another compound, especially an acid; most commonly, a compound of a nonmetallic oxide with water that reacts with water to form an acid.
- A compound derived from another compound (typically an acid) by removal of water, which often reacts with water to regenerate the original acid.
- More broadly in inorganic chemistry: an oxide of a nonmetallic element that forms an acid when combined with water (an acidic oxide).
"The chemist added acetic anhydride to the reaction mixture to drive the acetylation forward."
"Maleic anhydride is widely used in the production of resins and coatings."
"When sulfur trioxide dissolves in water, it behaves as the anhydride of sulfuric acid."
The plural follows standard English noun formation and is common in technical writing when referring to multiple compounds of this class.
"Cyclic anhydrides such as maleic anhydride are important intermediates in polymer synthesis."
Strip away water from certain acids and you get one of chemistry's most reactive workhorses — acetic anhydride is so useful it's carefully regulated because it's also a key precursor in illicit drug manufacture.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of anhydride
The word anhydride was coined in early 19th-century chemistry from Greek roots: the privative prefix 'an-' (meaning 'without') joined to 'hydor' (water), yielding the sense of 'without water.' It emerged as chemists such as those working in the Lavoisier tradition systematized the relationship between acids and their dehydrated oxides. It shares its Greek water-root with related terms like anhydrous and anhydrite, all describing substances or conditions lacking water.
How anhydride is actually used
Strictly technical vocabulary used almost exclusively in chemistry and related sciences; rarely encountered outside laboratory, industrial, or academic contexts. In organic chemistry the term usually refers to carboxylic acid anhydrides such as acetic or phthalic anhydride.
Easily confused with anhydride
Anhydrous is an adjective describing a substance containing no water, whereas an anhydride is a specific type of compound formed by removing water from another substance.
Anhydrite is a naturally occurring mineral (calcium sulfate), while an anhydride is a class of chemical compounds formed by dehydration, typically of acids.