anhydride

(noun)

Any compound formally derived from another (or from others) by the loss of a water molecule; a molecule with no water.

Related Terms

  • hydrate
  • carbohydrate

Examples of anhydride in the following topics:

  • Nomenclature

    • Anhydrides: The name of the related acid(s) is used first, followed by the separate word "anhydride". e.g.
    • (CH3(CH2)2CO)2O is butanoic anhydride & CH3COOCOCH2CH3 is ethanoic propanoic anhydride (or acetic propionic anhydride).
  • Substitution of the Hydroxyl Hydrogen

    • For example, phenol reacts easily with acetic anhydride to give phenyl acetate.
  • Acyl Group Substitution

    • Reactivity: acyl halides > anhydrides >> esters ≈ acids >> amides
    • Finally, anhydrides and esters have intermediate reactivities, with anhydrides being more reactive than esters.
    • Reactions #4 & 5 display the acylating capability of anhydrides.
    • Bear in mind that anhydrides may also be used as reagents in Friedel-Crafts acylation reactions.
    • Indeed, it is often possible to carry out reactions of amines with acyl chlorides and anhydrides in aqueous sodium hydroxide solution!
  • Reactions with Organometallic Reagents

    • Reaction of an excess of these reagents with acyl chlorides, anhydrides and esters leads to alcohol products, in the same fashion as the hydride reductions.
    • Esters are the most common carbonyl reactants, since they are cheaper and less hazardous to use than acyl chlorides and anhydrides.
    • Reaction with acyl chlorides, anhydrides and esters leads to alcohol products
  • Reactions at the α-Carbon

    • Acyl halides and anhydrides are more easily halogenated than esters and nitriles, probably because of their higher enol concentration.
    • In a similar fashion, acetic anhydride serves as a halogenation catalyst for acetic acid (first equation below).
    • Acetic anhydride serving as a halogenation catalyst for acetic acid (i) and substitution with malonic acid compound (ii)
  • Related Carbonyl Derivatives

    • Most of the functions are amides or esters, cantharidin being a rare example of a natural anhydride.
  • Substitution of the Hydroxyl Hydrogen

    • The electrophilic atom in the acid chlorides and anhydrides is colored red.
  • Naming Hydrates

    • A hydrate that has lost water is referred to as an anhydride.
    • An anhydride can normally lose water only with significant heating.
  • Characteristics of Specific Substitution Reactions

    • The Friedel-Crafts acylation reagent is normally composed of an acyl halide or anhydride mixed with a Lewis acid catalyst such as AlCl3.
    • The second makes use of an anhydride acylating reagent, and the third illustrates the ease with which anisole reacts, as noted earlier.
    • The H4P2O7 reagent used here is an anhydride of phosphoric acid called pyrophosphoric acid.
  • Reduction

    • Equivalent reductions of anhydrides have not been reported, but we might speculate that they would be reduced more easily than esters.
    • Acids, esters, anhydrides and acyl chlorides are all reduced to 1º-alcohols, and this method is superior to catalytic reduction in most cases.
    • Since acyl chlorides and anhydrides are expensive and time consuming to prepare, acids and esters are the most commonly used reactants for this transformation.
    • First, NaBH4 is often used in hydroxylic solvents (water and alcohols), and these would react with acyl chlorides and anhydrides.
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