Download Ethers General formula R-O-R` Properties Ethers are generally

Ethers
General formula R-O-R'
Properties
Ethers are generally unreactive, but due to the presence of the lone pairs on oxygen, unlike hydrocarbons,
they are soluble in concentrated sulfuric acid:
R-O-R' + H 2 SO4
R-O-R' + HSO 4
Nomenclature
The IUPAC rules name the R-O- group as an alkoxy group attached to the longest chain, however the
compounds are often named as ethers.
CH3OCH3
CH3OCH2 CH3
CH3CH2OCH3 CH2
dimethyl ether
diethyl ether or ether
methylethyl ether
methoxymethane
ethoxyethane
methoxyethane
OCH3
O
O
O
anisole
methoxybenzene
methylphenyl ether
ethylene oxide
oxirane
oxycyclopropane
furan
tetrahydrofuran
oxacyclopentane
O
Cl
O
Cl
O
Cl
O
Cl
1,4-dioxane
2,3,7,8-tetrachlorodibenzodioxin
Synthesis
1. From alcohols and phenols - the Williamson ether synthesis
2 ROH + 2 Na
2 RO- Na+ + H2
R-O-R' + X 2 RO- + R'X
This is an SN 2 reaction so is fast when R'X is a primary halide, but does not go when R'X is a
tertiary halide.
for example
2 CH3CH2O- Na+ + H2
2 CH3CH2OH + 2 Na
CH3CH2Obut
CH3CH2O
however
H3C
+ CH3 CH2 Cl
-
+
H3C
CH3
C O
CH3
CH3CH2OCH2 CH3
CH3
C Cl
CH3
CH3
C
H2C
+ Cl
+
CH3CH2OH
+
Cl
CH3
CH3
C O CH2CH3
CH3
H3C
+ CH3 CH2Cl
For the Williamson ether synthesis to go, the alkoxide can be primary, secondary or tertiary, but the
alkyl halide should be primary or secondary.
O
OH
+
+ H2 O
NaOH
OCH2 CH2 CH3
O
+ CH3 CH2CH2Br
Br
but
CH3CH2CH2O
+
no reaction
Preparation of epoxides by internal Williamson type synthesis
CH2=CH 2 + Br2 + H2O
Br
H2C CH2
OH
OHOH
1) Br2/H2 O
2) HO
Br
H2C CH
O
O
O
-Br
2. Alkoxymercuration
CH3
CH3 Hg(OCOCH 3)2/CH3 CH2OH
H2C C
CH 3
H2C C
CH 3
Hg OCH2 CH3
O C CH 3
NaBH 4, HO-
CH 3
H3C C
CH 3
OCH2 CH3
O
Almost any alkene and any alcohol can be used in this synthesis
HC CH 2
e.g.
OH
1) Hg(OCOCH3)2/CH3 CHCH3
CH 3
O C CH 3
H
CH CH3
2) NaBH4, OHReactions of ethers
Inert chemically
The most important reaction is cleavage by hydrogen iodide
2 RI
R-O-R' + 2HI
e.g.
H 3C
excess HI
CH O CH CH3
CH 3
CH 3
HI
100oC
+
H2 O
2 H3C
CH-I
CH3
+
H2 O
I-CH 2CH2CH 2CH2-I
O
Epoxides are very reactive due to the angle strain in the 3-membered ring. They are very useful in
syntheses
O
HO
H 2C
0oC
+ HCl
CH2
Cl
Epoxides can be used in the synthesis of alcohols
O
RCH 2CH2OMgX
+ RMgX
H2O
RCH 2CH2OH
This reaction can be used to increase the alkyl chain by 2 carbon units
Synthesis of cis-7,8-epoxy-2-methyloctadecane
H
H
O
cis 7,8-epoxy-2-methyl-octadecane
Synthesise this molecule from
HC
and any inorganic reagents needed.
CH , Br (CH 2)9CH3 and
Br