Low-molecular-weight ethers are flammable gases (dimethyl ether) or liquids (methyl ethyl ether or diethyl ether) that can produce explosive mixtures when they evaporate and mix with air. Ethers form peroxides if exposed to oxygen or air during storage; the ether peroxides can detonate with friction, shock, or heat, releasing enough energy to start a secondary fire in the unperoxidized ether.

Ethers tend to form unstable peroxides when exposed to oxygen. Ethyl, isobutyl, ethyl tert-butyl, and ethyl tert-pentyl ether are particularly hazardous in this respect. Ether peroxides can sometimes be observed as clear crystals, which can be shock sensitive, deposited on containers or along the surface of the liquid. Ethers usually act as weak Lewis bases. They form salts with strong acids and addition complexes with Lewis acids. The complex between diethyl ether and boron trifluoride is an example. Ethers may react violently with strong oxidizing agents. In other reactions, which typically involve the breaking of the carbon-oxygen bond, ethers are relatively unreactive.

As a group, ethers are moderately toxic. The lower-molecular weight ethers are powerful rapid-acting narcotics by inhalation. Toxic effects from these compounds are usually acute, not chronic. Swallowing one to two ounces of a liquid ether may be fatal.

Ethers contain an oxygen atom bonded to two organic groups, that is, they have general formula R-O-R', where the R and R' represent organic groups. Ethers are prepared by the Williamson synthesis (the reaction of a metallic alkoxide with an alkyl halide) and also by the reaction of alkyl hydrogen sulfates with alcohols. This amounts to the mixing of alcohols with sulfuric acid and heating. This process gives ethers as co-products in the preparation of alcohols from olefins in the presence of H2SO4.

Phenyl ether, ethyl ether, allyl ethyl ether, anisidine, anisole, butyl methyl ether, butyl vinyl ether, diallyl ether, isopropyl ether, divinyl ether, methyl ether.