anhydride

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.