H O H R O H R O R
water alcohol ether
Structure and nomenclature of ethers
Ethers are compounds of formula R -O-R', where R and R' may be
alkyl groups or aryl groups.
Common names (Alkyl Alkyl Ether Names)
Common names of ethers are formed by naming the two alkyl
groups on oxygen and adding the word ether. Under the current
system, the alkyl groups should be named in alphabetical order.
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H3C-O-CH3 H3C-CH2-O-CH2-CH3
H2C=CH-O-CH=CH2
Common Dimethyl ether Diethyl ether Divinyl ether
IUPAC Methoxy methane
Ethoxy ethane
H3C-O-C6H13 H3C-O-CH2-CH3 H3C-O-CH=CH2
Common Hexyl methyl ether
Ethyl methyl ether Methyl vinyl ether
IUPAC Methoxy hexane
mehoxy ethane Methoxy ethene
Examples
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Common: Diphenyl etherIUPAC : Phenoxy benzene
Common: Methyl Phenyl ether (anisole)IUPAC : Methoxy benzene
CH3CH3
OCH3
CH3CH3
O
CH3
OCH3
3-Methoxyhexane 5-Ethoxy-2-heptene 1-Phenoxy-1-propene
Examples
Physical Properties of EtherBoiling Points
The boiling points of ethers are lower than those of alcohols having the
same molecular weights.
Solubility in water Ethers are much less soluble in water than alcohols.More water-soluble than hydrocarbons of similar molecular weight.
compound Formula MW Bp (°C)
ethanol CH3-CH2-OH 46 78
Dimethyl ether
CH3-O-CH3 46 -25
propane CH3-CH2-CH3 44 -42
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Preparation of ehers
Ethers by dehydration of alcohols
The dehydration of alcohols takes place in the presence of acid catalysts
(H2SO4, H3PO4) under controlled temperature. The general reaction for
ether formation is:
R O H H O R R O R+H
+
heat+ H2O
Examples
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2 CH3HO H2SO4, 140 C CH3OH3C + H2O
methyl alcohol methyl ether
2 CH2CH3HO H2SO4, 140 C CH2CH3OH3CH2C + H2O
ethyl alcohol ethyl ether
(100%)
(88%)
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The Williamson synthesis of ethers
O- Na+RROR + NaX
sodium alkoxide ether
+ R X
O- Na+ROR + NaX
sodium phenoxide ether
+ R X
alkyl halide
alkyl halide
The alkoxide is commonly made by adding Na or K to the alcohol
Examples
OH O
CH3CH2 Br
OCH2CH3
Na
Na+
+ NaBr
cyclohexanol ethoxycyclohexane sodium
cyclohexyloxide
8
OH1) Na
2) CH3-I
OCH3
3,3-dimethyl-2-pentanol 2-ethoxy-3,3-dimethypentane
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3,3-dimethyl-2-pentanol 2-Methoxy-3,3-dimethypentane
Cleavage of ethers by hot concentrated acids
When ethers are heated in concentrated acid solutions, the ether
linkage is broken
General equation:R O R H X R OH R X+
heat
(concentrated)
+
Specific example
CH3CH2 O CH2CH3 H I CH3CH2OH CH3CH2I+heat
(concentrated)
+
The acids most often used in this reaction are HI, HBr, and HCl.
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Reaction of Ether
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CH3CH2 O CH2CH3 + 2HBr
(conc, excess)
heat2 CH3CH2Br + H2O
If an excess of acid is present, the alcohol initially produced
is converted into an alkyl halide by the reaction.
For example
R O R H X R X+ 2 + H2O2
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Epoxides are cyclic ethers in which the ether oxygen is part of a
three-membered ring. C C
O
an epoxide
The simplest and most important epoxide is ethylene oxide.
O
ethylene oxide
11
Cyclic EthersEpoxide
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Peroxyacid Epoxidation
Peroxyacids (sometimes called peracids) are used to convert
alkenes to epoxides. If the reaction takes place in aqueous acid, the
epoxide opens to a glycol. Because of its desirable solubility
properties, meta-chloroperoxybenzoic acid (MCPBA) is often used
for these epoxidations.
R-C-O-O-H
O O
R-C-O-H
O
+ +
O
Cl
C-O-O-H
O
MCPBA
CH2Cl2
epoxycyclohexanecyclohexene
MCPBA :
Example
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Their reactivity is due to the strain in the three-membered ring, which
is relieved when the epoxide ring is opened after a reaction has taken
place.
Examples of ring-opening reactions of ethylene oxide that form
commercially important products are:
1- Epoxides open in acidic solutions to form glycols.
H3OCH CH
O
R CH CH R
OH
OH
R R
+
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2- Epoxides open in acidic alcohol solutions to form 2-alkoxy alcohols.
3- When an epoxide reacts with a hydrohalic acid ( HCl,HBr, or HI), a
halide ion attacks the protonated epoxide.
4- Reactions of Epoxides with Grignard and Organolithium Reagents
15
H X CH CH
O
R CH CH R
OH
X
R R+
R' MgX CH CH
O
R CH CH R
R'
OH
R' Li
R R+1) ether
2) H3O+
or
CH3 OH CH CH
O
R CH CH R
OH
O
R R
CH3+
+.. H3O
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Exercise 1
Give a correct name for each of the following compounds.
CH2CH3 O CH2CH2CH3
CH2=CHCH2 O CH2CH=CH2
O CH2CH3
CH3CHCH2CH3
O CH3
CH3CH2CHCH=CH2
O CH2CH3
OCH3
O CH3
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Exercise 2
Propose a Williamson synthesis of 3-butoxy-1,1-
dimethylcyclohexane from 3,3-dimethylcyclohexanol and butanol.
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