The properties of ethers are divided into physical and chemical properties. Overall, their chemical properties are relatively stable, as detailed below:
Physical Properties
State and Odor: At room temperature, only dimethyl ether and methyl ethyl ether are gases; most ethers are colorless liquids with a characteristic odor.
Melting and Boiling Points: Because ether molecules cannot form hydrogen bonds, their boiling points are much lower than alcohols with the same number of carbon atoms, and close to those of alkanes with similar molecular weights.
Solubility: Easily soluble in organic solvents. Lower ethers have some solubility in water, while higher ethers are sparingly soluble. Cyclic ethers such as tetrahydrofuran and 1,4-dioxane, due to exposed oxygen atoms, can form hydrogen bonds with water and are completely miscible with water.
Density: Most ethers have a density less than water and are flammable liquids; their vapors can form explosive mixtures with air.
Chemical Properties
Ethers (except cyclic ethers) are generally chemically inert, with stability slightly lower than alkanes. They are stable to alkali metals, strong bases, oxidizing agents, and reducing agents. They do not react with metallic sodium at room temperature, therefore metallic sodium is often used to dry ethers, making them suitable as organic solvents.
Their characteristic reactions mainly include:
Formation of ganate salts: The oxygen atom in the ether bond has a lone pair of electrons, which can act as a weak base to combine with concentrated strong acids (such as concentrated sulfuric acid and concentrated hydrochloric acid) to form ganate salts, thus dissolving in concentrated strong acids. This property can be used to separate and identify ethers from alkanes/haloalkanes; it can also react with Lewis acids such as boron trifluoride, aluminum trichloride, and Grignard reagents to form ganate salts.
Ether bond cleavage: Under heating conditions, ethers can react with hydrohalic acids, breaking the ether bond to form an alcohol and a haloalkane; if the hydrohalic acid is in excess, the generated alcohol will continue to react to give two molecules of haloalkane. The reactivity is generally HI > HBr > HCl.
Auto-oxidation: Ethers such as diethyl ether, upon prolonged exposure to air and light, will generate non-volatile explosive peroxides. Residual peroxides during distillation can trigger an explosion. Before using ethers stored for extended periods, peroxide levels must be tested; if a positive result is detected, the ether must be treated before use.
Special Properties of Cyclic Ethers: Cyclic ethers (such as epoxides) exhibit ring strain, making them chemically more reactive. They can undergo ring-opening reactions under acid or base catalysis and react with a variety of nucleophiles.