1 4 Ethers, Epoxides, and Sulfides Ethers are compounds of formula R - 0 -R', where R and R' may be alkyl groups or aryl (benzene ring) groups. Like alcohols, ethers are related to water, with alkyl groups replacing the hydrogen atoms. In an alcohol, one hydrogen atom of water is replaced by an alkyl group. In an ether, both hydrogens are replaced by alkyl groups. The two alkyl groups are the same in a symmetrical ether and different in an un-symmetrical ether. H-O -H water Examples of ethers diethyl ether (a symmetrical ether) R-O -H alcohol R-O -R' ether < l-0-CH, methyl phenyl ether (an unsymmetrical ether) Q tetrahydrofuran (a symmetrical, cyclic ether) As with other functional groups, we will discuss how ethers are formed and how they react. Ethers (other than epoxides) are relatively unreactive, however, and they are not frequently used as synthetic intermediates. Because they are stable with many types of reagents, ethers are commonly used as solvents for organic reactions. In this chapter, we consider the properties of ethers and how these properties make ethers such valuable solvents for organic reactions. The most important commercial ether is diethyl ether, often called "ethyl ether," or simply "ether." Ether is a good solvent for reactions and extractions, and it is used as a volatile starting fluid for diesel and gasoline engines. Ether was used as a surgical anesthetic for over a hundred years (starting in 1 842), but it is highly flammable, and patients often vomited as they regained consciousness. Several compounds that are less flammable and more easily tolerated are now in use, including nitrous oxide (N20) and halothane (CF3- CHClBr). 14-2A Structure and Polarity of Ethers Like water, ethers have a bent structure, with an sp3 hybrid oxygen atom giving a near-ly tetrahedral bond angle. In water, the non bonding electrons compress the H -0 - H bond angle to 104.5°, but in a typical ether, the bulk of the alkyl groups enlarges the l S-crown-6 with K+ solvated 1 4-1 Introduction 1 4-2 Physical Properties of Ethers 623
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