CHM 247 CH.18
Ethers and Epoxides; Thiols and Sulfides
• Ether: A compound that has 2 organic substituents bonded to the same oxygen atom,
• Thiol: A thiol compound containing the –SH functional group.
• Sulfide: A compound that has 2 organic substituents bonded to the same sulfur atom,
• Common ethers are diethyl ether and tetrahydrofuran.
18.1 Names and Properties of Ethers
• Simple ethers with no other functional groups are names by identifying the 2 organic
substituents and adding the word ether.
• If other functional groups are present, the ether part is considered an alkoxy substituent
• The oxygen is sp hybridized. It gives the molecule a slight dipole moment, leading to a
slightly higher boiling point.
• Ethers are relatively stable and non-reactive. Some react slowly with the oxygen in air to
18.2 Synthesis of Ethers
• Can use a sulfuric acid catalyzed reaction of alcohols. Takes place via N S 2 mechanism.
Only works with primary alcohols.
The Williamson Ether Synthesis
• The alkyl halide needs to be primary.
• Alkoxymercuration: A method for synthesizing ethers by mercuric-ion catalyzed addition
of an alcohol to an alkene followed by demercuration on treatment with NaBH .4
18.3 Reactions of Ethers: Acidic Cleavage
• Ethers can be cleaved by strong acids. • Br or I can be used.
• The mechanism varies depending on the functional group.
• Ethers with only primary or secondary alkyl groups react by a N 2 mechanism in which X
attacks at the less hindered site.
18.5 Cyclic Ethers: Epoxides
• Similar to non-cyclic ethers.
• 3 membered rings are one of the few groups that behave differently. Epoxides are also
• Crown ethers have their ether groups pointing inwards, allowing another ion to bond.
They have enhanced reactivity.
18.6 Reactions of Epoxides: Ring-Opening
Acid-Catalyzed Epoxide Opening
• Dilute acid is enough to cause hydrolys