ethers
DESCRIPTION
Ethers. Ethers are compounds with the general formula: R-O-R’ symmetrical ethers: R = R’ unsymmetrical ethers: R = R’ two lone pairs of electrons on oxygen sp 3 hybrid oxygen atom bent molecular geometry. Ethers. Ethers are commonly used as solvents in organic reactions. - PowerPoint PPT PresentationTRANSCRIPT
Ethers Ethers are compounds with the general
formula: R-O-R’
symmetrical ethers: R = R’unsymmetrical ethers: R = R’
two lone pairs of electrons on oxygen
sp3 hybrid oxygen atom bent molecular geometry
Ethers Ethers are commonly used as solvents in
organic reactions. Polar molecules no hydrogen bonding between ether
moleculeslower BP than comparable alcohols
serves as hydrogen bond acceptor in the presence of alcohols, amines, or carboxylic acids
Nomenclature of Ethers Common Names:
Name the two alkyl groups and add the word etheralphabetical order in order of increasing complexity
use prefix “di” to indicate both alkyl groups are identicalif only one alkyl group is described in name, it implies the ether is symmetrical
OR
Nomenclature of Ethers Examples of Common Names
CH3CH2OCH3 methyl ethyl ether
CH3CH2OCH2CH3 diethyl ether or ethyl ether
Ethers IUPAC Names (Alkoxy alkane) :
Ethers names as alkoxy alkanesUse the more complex alkyl group as the base name
The other alkyl group is named as an alkoxyl group
Examples
CH3CH2OCH3 methoxyethane
CH3CH2OCH2CH3 ethoxyethane
Ethers
Example: Name the following ethers.
OCH2CH3
CH2CH3
O
Ethers
Example: Draw the following compounds.
Methoxycyclopentane
Ethyl t-butyl ether
Chloromethyl methyl ether
(1R, 2R)-2-methoxycyclohexanol
Nomenclature of Ethers Cyclic ethers are heterocyclic compounds:
compounds containing a ring in which one or more ring atoms is an element other than carbon
Epoxide (oxirane): three membered cyclic ether
O
Cl
OO
Cl
O
O
O
Ethylene oxideoxirane
epichlorohydrin cyclohexene oxide
Nomenclature of Ethers Furan :
a five-membered aromatic cyclic ether
Tetrahydrofuran (oxolane): saturated, five-membered cyclic ether
O
O
O
O
O
O
Nomenclature of Ethers Pyran (Oxane):
an unsaturated, six-membered cyclic ether
Dioxane: heterocyclic ether with two oxygen
atoms in a six-membered ring
O
O
O
O O
O
O
O
O
1,4-dioxane
Synthesis of Ethers Williamson Ether Synthesis
SN2 attack of an alkoxide ion on an unhindered methyl or primary alkyl halide or tosylate
Synthesis of Ethers Alkoxymercuration-Demercuration:
formation of Markovnikov ether from an alkene
“anti” addition to the double bond
Reagents:(1) Hg(OAc)2, ROH(2) NaBH4
RRR
Synthesis of Ethers Examples:
(1) Hg(OAc)2
CH3CH
2OH
(2) NaBH4
CH3
CH3
CH3
H OCH2CH
3
CH3H
3CH
3C
H CH3
OCH2CH
3
Synthesis of Ethers Epoxidation of Alkenes
formation of an epoxide from an alkene using a peroxyacid
Reagents: MCPBA CH3CO3H
Retains stereochemistry of C=C
Synthesis of Ethers Example:
MCPBA
CH2Cl2O
100%
Synthesis of Ethers Base-Promoted Cyclization of Halohydrins
formation of epoxides from halohydrin via internal SN2 attack of an alkoxide ion on an adjacent carbon containing a halogen
Reagents: NaOH (aq)
Synthesis of Ethers Example:
OH
Reactions of Ethers Autoxidation of Ethers:
spontaneous oxidation of ethers to hydroperoxides and dialkyl peroxides in the presence of atmospheric oxygen
Hydroperoxides and dialkyl peroxides are highly explosive do not distill to dryness use ether promptly test old cans of ether before use
Reactions of Ethers Acid-Catalyzed Ring Opening of Epoxides
SN2 attack of water or alcohol molecule on a protonated epoxide ring
Using H+/H2O:
anti stereochemistry Water attacks at the more substituted
carbon
Reactions of Ethers Using H+/ROH:
anti stereochemistry ROH attacks at the more substituted
carbon
Reactions of Ethers Base-Catalyzed Ring Opening of Epoxides:
SN2 attack of OH- or RO- on an epoxide ring
Anti stereochemistry OH- and RO- attack at the least hindered
(least substituted) carbon in the epoxide ring
OH
Reactions of Ethers Examples:
Reactions of Ethers Reactions of Epoxides with Grignard and
Organolithium Reagents Attack of RMgX or RLi on the least
hindered carbon in the epoxide ring forming an alcohol
Reactions of Ethers Example:
(1) Mg/ether
(2)
(3) H3O
+
BrO
CH3
OH
Ethers
Examples: Predict the product of each of the following reactions.
MCPBA
CH2Cl
2
HCH
3
Ph
CH2CH
3
Ethers
Examples:
(1) Mg/ether
(2)
(3) H3O
+
NaOCH3
CH3OH
(1) Hg(OAc)2
CH3CH
2OH
(2) NaBH4
BrO
CH3
OH
O
CH3
(1) Mg/ether
(2)
(3) H3O
+
NaOCH3
CH3OH
(1) Hg(OAc)2
CH3CH
2OH
(2) NaBH4
CH3CHCH
3 O
CH3
O
CH3
Br
O
CH3NaOCH3
CH3OH
Ethers
Example: How would you prepare the following compounds from the reactant given?
CH3O
OH
CH3CH
2C CH
3CH
2CCH
3
CH3O
OH
CH
OH