1911 Encyclopædia Britannica/Ethers
ETHERS, in organic chemistry, compounds of the general formula R·O·R′, where R, R′ = alkyl or aryl groups. They may be regarded as the anhydrides of the alcohols, being formed by elimination of one molecule of water from two molecules of the alcohols; those in which the two hydrocarbon radicals are similar are known as simple ethers, and those in which they are dissimilar as mixed ethers. They may be prepared by the action of concentrated sulphuric acid on the alcohols, alkyl sulphuric acids being first formed, which yield ethers on heating with alcohols. The process may be made a continuous one by running a thin stream of alcohol continually into the heated reaction mixture of alcohol and sulphuric acid. Benzene sulphonic acid has been used in place of sulphuric acid (F. Krafft, Ber., 1893, 26, p. 2829). A. W. Williamson (Ann., 1851, 77, p. 38; 1852, 81, p. 77) prepared ether by the action of sodium ethylate on ethyl iodide, and showed that all ethers must possess the structural formula given above (see also Brit. Assoc. Reports, 1850, p. 65). They may also be prepared by heating the alkyl halides with silver oxide.
The ethers are neutral volatile liquids (the first member, methyl ether, is a gas at ordinary temperature). Phosphorus pentachloride converts them into alkyl chlorides, a similar decomposition taking place when they are heated with the haloid acids. Nitric acid and chromic acid oxidize them in such a mariner that they yield the same products as the alcohols from which they are derived. With chlorine they yield substitution products.
Methyl ether, (CH3)2O, was first prepared by J. B. Dumas and E. Péligot (Ann. chim. phys., 1835,  58, p. 19) by heating methyl alcohol with sulphuric acid. It is best prepared by heating methyl alcohol and sulphuric acid to 140° C. and leading the evolved gas into sulphuric acid. The sulphuric acid solution is then allowed to drop slowly into an equal volume of water, when the methyl ether is liberated (E. Erlenmeyer and A. Kriechbaumer, Ber., 1874, 7, p. 699). It is a pleasant-smelling gas, which burns when ignited, and may be condensed to a liquid which boils at 23.6º C. It is somewhat soluble in water and readily soluble in alcohol, and concentrated sulphuric acid. It combines with hydrochloric acid gas to form a compound (CH3)2O·HCl (C. Friedel, Comptes rendus, 1875, 81, p. 152). Methyl ethyl ether, CH3·O·C2H5, is prepared from methyl iodide and sodium ethylate, or from ethyl iodide and sodium methylate (A. W. Williamson, Ann., 1852, 81, p. 77). It is a liquid which boils at 10.8º C.