L5 - Ethers

ether, any of a class of organic compounds characterized by an oxygen atom bonded to two alkyl or aryl groups. Ethers are similar in structure to alcohols, and both ethers and alcohols are similar in structure to water. In an alcohol one hydrogen atom of a water molecule is replaced by an alkyl group, whereas in an ether both hydrogen atoms are replaced by alkyl or aryl groups.

Ethers are also important in medicine and pharmacology, especially for use as anesthetics. For example, ethyl ether (CH₃CH₂−O−CH₂CH₃), simply known as ether, was first used as a surgical anesthetic in 1842. Codeine, a potent pain-relieving drug, is the methyl ether of morphine. Because ether is highly flammable, it has largely been replaced by less-flammable anesthetics, including nitrous oxide (N₂O) and halothane (CF₃−CHClBr).

Ethyl ether is an excellent solvent for extractions and for a wide variety of chemical reactions. It is also used as a volatile starting fluid for diesel engines and gasoline engines in cold weather. Dimethyl ether is used as a spray propellant and refrigerant. Methyl t-butyl ether (MTBE) is a gasoline additive that boosts the octane number and reduces the amount of nitrogen-oxide pollutants in the exhaust. The ethers of ethylene glycol are used as solvents and plasticizers.

Ethers lack the hydroxyl groups of alcohols. Without the strongly polarized O−H bond, ether molecules cannot engage in hydrogen bonding with each other.Because ether molecules cannot engage in hydrogen bonding with each other, they have much lower boiling points than do alcohols with similar molecular weights. For example, the boiling point of diethyl ether (C₄H₁₀O) is 35 °C, but the boiling point of 1-butanol (or n-butyl alcohol; C₄H₁₀O) is 118 °C. In fact, the boiling points of ethers are much closer to those of alkanes with similar molecular weights; the boiling point of pentane (C₅H₁₂) is 36 °C, close to the boiling point of diethyl ether.