1. Ethers & Epoxides
Unit 12

2. Structure
The functional group of an ether is an oxygen atom bonded to two carbon atoms
in dialkyl ethers, oxygen is sp3 hybridized with bond angles of approximately 109.5°.
in dimethyl ether, the C-O-C bond angle is 110.3°

3. Structure
in other ethers, the ether oxygen is bonded to an sp2 hybridized carbon
in ethyl vinyl ether, for example, the ether oxygen is bonded to one sp3 hybridized carbon and one sp2 hybridized carbon

4. Nomenclature: ethers IUPAC: the longest carbon chain is the parent
name the OR group as an alkoxy substituent
Common names: name the groups bonded to oxygen in alphabetical order followed by the word ether O H C H 3 C H 3 O C H 3 2 O O C H 2 3 C H 3
Ethoxyethane
(Diethyl ether)
trans-
2-Ethoxy-
cyclohexanol
2-Methoxy-2-
methylpropane (
tert-
Butyl methyl ether)

5. Nomenclature: ethers
Although cyclic ethers have IUPAC names, their common names are more widely used
IUPAC: prefix ox- shows oxygen in the ring
the suffixes -irane, -etane, -olane, and -ane show three, four, five, and six atoms in a saturated ring

6. Physical Properties
Although ethers are polar compounds, only weak dipole-dipole attractive forces exist between their molecules in the pure liquid state

7. Physical Properties Boiling points of ethers are
lower than alcohols of comparable MW
close to those of hydrocarbons of comparable MW
Ethers are hydrogen bond acceptors
they are more soluble in H2O than are hydrocarbons

8. Preparation of Ethers Acid-catalyzed dehydration of alcohols
diethyl ether and several other ethers are made on an industrial scale this way
a specific example of an SN2 reaction in which a poor leaving group (OH-) is converted to a better one (H2O)

9. Epoxides
Epoxide: a cyclic ether in which oxygen is one atom of a three-membered ring
simple epoxides are named as derivatives of oxirane
where the epoxide is part of another ring system, it is shown by the prefix epoxy-
common names are derived from the name of the alkene from which the epoxide is formally derived H H H 1 2 3 C H 3 H 3 C H 2 C C H 2 O C C O 1 O 2 H
Oxirane
(Ethylene oxide)
cis-
2,3-Dimethyloxirane (
2-Butene oxide)
1,2-Epoxycyclohexane
(Cyclohexene oxide)

10. Synthesis of Epoxides
Ethylene oxide, one of the few epoxides manufactured on an industrial scale, is prepared by air oxidation of ethylene A g 2 C H = + O 2 2 H 2 C C H 2 O
Oxirane
(Ethylene oxide)

11. Synthesis of Epoxides
The most common laboratory method is oxidation of an alkene using a peroxycarboxylic acid (a peracid) O O C O H C O H O M g 2 + C H 3 O C O -
Peroxyacetic acid
(Peracetic acid) C l O 2
meta-
chloroperoxy-
benzoic acid
(MCPBA)
Magnesium
monoperoxyphthalate
(MMPP)

12. Synthesis of Epoxides
Epoxidation of cyclohexene

13. Synthesis of Epoxides Epoxidation is stereospecific:
epoxidation of cis-2-butene gives only cis-2,3-dimethyloxirane
epoxidation of trans-2-butene gives only trans-2,3-dimethyloxirane

14. Reactions of Epoxides Acid-catalyzed ring opening
in the presence of an acid catalyst, such as sulfuric acid, epoxides are hydrolyzed to glycols H + O H + H 2 O O H O
Oxirane
(Ethylene oxide)
1,2-Ethanediol
(Ethylene glycol)

15. Crown Ethers
Crown ether: a cyclic polyether derived from ethylene glycol or a substituted ethylene glycol
the parent name is crown, preceded by a number describing the size of the ring and followed by the number of oxygen atoms in the ring

16. Crown Ethers
The diameter of the cavity created by the repeating oxygen atoms is comparable to the diameter of alkali metal cations
18-crown-6 provides very effective solvation for K+

17. Thioethers The sulfur analog of an ether
IUPAC name: select the longest carbon chain as the parent and name the sulfur-containing substituent as an alkylsulfanyl group
common name: list the groups bonded to sulfur followed by the word sulfide

18. Nomenclature Disulfide: contains an -S-S- group
IUPAC name: select the longest carbon chain as the parent and name the disulfide-containing substituent as an alkyldisulfanyl group
Common name: list the groups bonded to sulfur and add the word disulfide