Ethers: preparation and properties
Compounds of general formula R–O–R′ in which an oxygen atom links two radicals are ethers; one can regard them as alcohols whose –OH hydrogen is replaced by a radical, or as water with both hydrogens replaced. The rational name is the radicals plus “ether”: dimethyl ether CH₃–O–CH₃, diethyl ether C₂H₅–O–C₂H₅, methyl ethyl ether; in the systematic name the larger radical is the alkane and the smaller one an alkoxy group: methoxyethane CH₃–O–C₂H₅. Isomerism: by radical structure and interclass — ethers are isomers of monohydric alcohols (C₃H₈O: propanol-1, propanol-2 and methyl ethyl ether). Preparation: intermolecular dehydration of an alcohol with H₂SO₄ below 140 °C: 2C₂H₅OH → C₂H₅–O–C₂H₅ + H₂O; in industry alcohol vapour is passed over Al₂O₃. Dimethyl and methyl ethyl ether are gases, middle members liquids; ethers are sparingly soluble in water and, lacking hydrogen bonds, boil lower than alcohols. Ethers are chemically inert: they do not react with alkali, dilute acid or sodium under ordinary conditions (this distinguishes them from alcohols), so they are used as solvents; HI cleaves the C–O bond: CH₃–O–CH₃ + HI → CH₃OH + CH₃I. Diethyl ether is extremely flammable, its vapour forms explosive mixtures with air, and it was once used in medicine as an anaesthetic.
Write alcohol–ether isomer sets for C₂H₆O, C₃H₈O and C₄H₁₀O. In each set say which boils higher and why. No experiments with ethers — they are extremely flammable.