Ether

Definition

Ethers are organic molecules with the general structure R1-O-R2, where R1 and R2 are identical for symmetrical ethers. The radicals can be aliphatic or aromatic. Cyclic ethers exist, such as tetrahydrofuran (THF). Ethers can be prepared using, for example, Williamson’s synthesis:

  • R1-X + R2-O–Na+ R1-O-R2 + NaX

X stands for halogens

Nomenclature

Trivial names are formed with the suffix -ether, for example, methylphenyl ether (anisole) or diethyl ether. Official nomenclature uses prefixes such as methoxy, ethoxy, and phenoxy.

Representative

Ethers include, for example:

  • Diethyl ether
  • Dimethyl ether
  • Ethyl methyl ether
  • Epoxides
  • Glycosides
  • Non-aromatic heterocycles with oxygen atoms, e.g. tetrahydrofuran, tetrahydropyran, dioxane.
  • Macrogols (PEG, polymers).

Properties

  • Ethers are hydrogen bond acceptors but not donors.
  • Ethers have low boiling points comparable to those of alkanes. The reason is weak intermolecular interactions. This, for example, in contrast to the alcohols.
  • Ethers with a low molecular mass are soluble in water due to H-bridge formation.
  • It should be noted that the low ethers are volatile, highly flammable, explosive and heavier than air (experiment with the “ether trough”).
  • It must also be noted that ethers such as diethyl ether can form explosive peroxides over time due to auto-oxidation.
  • Ethers can form complexes due to the free electrons of oxygen.

Reactions

Ethers are generally chemically inert and less reactive than, for example, alcohols, amines, and carboxylic acids. However, they can be protonated and cleaved with strong acids such as HI, HBr, and HCl:

Reactivity: HI > HBr >> HCl

In pharmacy

Many active pharmaceutical ingredients and excipients are ethers, and simple ethers such as diethyl ether have historically been used as anesthetics. Ethers such as dimethyl ether are used as propellants (blowing gases), for example, in the production of foams. They are also included in cold sprays and are used for the cryotherapy of warts. In chemistry, ethers are used as solvents and for extractions, among other things, because of their low reactivity.