ETHERS AND EPOXIDES
By
Dr. Nahed Nasser
1
THE CHEMISTRY OF Ethers and
Epoxides
CONTENTS
• Structure and classification of ethers
• Nomenclature of ethers
• Physical properties of ethers
• Preparation of ethers from alcohols and alkyl halides
• Reactions of opened ethers with HI
• Synthesis of epoxides (3-memebered cyclic ethers) from alkenes
• Reactions of epoxides with H2O, ROH, HX, LiAlH4, phenol, Grignard reagent and NH3
2
STRUCTURE OF ETHERS
Ether: is a class of organic compounds that contain an ether group — an oxygen atom
connected to two alkyl or aryl groups via σ bonds. thus Ethers feature C-O-C linkage — of general
formula R–O–R
Types of ethers
• Symmetrical
ethers : in that the two substituents are the same
i.e. R-O-R or Ar-O-Ar
• Unsymmetrical ethers
are those have two different substituents
I
Cl
H3C
i.e. R-O-R’ or R-O-Ar or Ar-O-Ar ’ CH3
Nomeclature OF Ethers H C C Br
3
CH3
Common names
•The common names of ethers are derived by naming the alkyl
groups bonded to the oxygen then listing them in alphabetical
order followed by the word "ether".
The common alkoxy substituents are given names derived from
their alkyl component,
Alkyl group
Name
Alkoxy
Group Name
CH3–
Methyl
CH3O–
Methoxy
CH3CH2–
Ethyl
CH3CH2O–
Ethoxy
(CH3)2CH–
Isopropyl
(CH3)2CHO–
Isopropoxy
(CH3)3C–
tert-Butyl
(CH3)3CO–
tert-Butoxy
C6H5–
Phenyl
C6H5O–
Phenoxy
O
H3C
CH3 H3C CH2 O
O
CH2CH3
Common Dimethyl ether Diethyl ether
IUPAC
Methoxy methane Ethoxy ethane
H2C
CH O
CH
Divinyl ether
CH2
Diphenyl ether
Phenoxy benzene
O
CH3
H3C
O
C6H13
H3C
O
CH2CH3
H3C
O
CH
CH2
Common Hexyl methyl ether Ethyl methyl ether Methyl vinyl ether Methyl Phenyl ether
(anisole)
IUPAC
Methoxy hexane
methoxy ethane Methoxy ethene Methoxy benzene
H3C
O
H3C
CH3
CH3
O
CH3
IUPAC 3-Methoxyhexane
H3C
CH3
5-Ethoxy-2-heptene
O
Propenyloxy benzene
Physical Properties
Solubility :
Ethers are polar compounds because of the polar nature of both the C-O bonds
due to the high electronegativity of the O atom compared to carbon atom.
Thus they can be involved in H-bonding with systems able to donate H (e.g.
water). Consequently their solubility in aqueous media is similar to
R
analogous alcohols.
H
O
O
R
H
H-bonds
Boiling point :
O
R
R
An ether cannot form hydrogen bonds with other ether molecules since there
is no H to be donated resulting in lower melting and boiling points compared
to analogous alcohols.
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom,
like nitrogen, oxygen or fluorine. The hydrogen must be covalently bonded to another
electronegative atom to create the bond. These bonds can occur between molecules
(intermolecularly), or within different parts of a single molecule (intramolecularly)..
Intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C).
Q-Ethanol C2H5OH and methyl ether CH3OCH3 have the same
6
weight. Which has a higher boiling point?
Preparation of Ethers
1- Dehydration of alcohols:
°C
°C
2- The Williamson synthesis :
-
RO Na
+
+
R'X
-
O Na
R-O-R'
+ H3C
-
H3C
NaX
O
+
O Na
+
+
+
Br
H3C
+
CH3
Br
H3C
O
NaBr
CH3
+
NaBr
Reactions of Ethers
+
R-O-R'
H3C
CH3
O
+
HI
HI
H2O / Heat
H2O / Heat
H3C
+
R-OH
R'-I
OH
+
I
H3C
O
CH3
+
HI
H2O / Heat
OH
+
H3C
I
Cyclic Ethers
O
O
O
O
O
IUPAC
Oxirane
Oxetane
Common Ethylene oxide Trimethylene oxide
O
Oxlane
Oxane
Tetrahydrofurane
Tetrahydropyrane
Preparation of cyclic ethers
O
H2C
+
CH2
Ag / 250 °C
O2
Ethene
Oxirane
OH
O
NaOH
Cl2 / H2O
H3C
CH2
H3C
H3C
Propene Oxide
Cl
Propene
O
Ph CO3H
Perbenzoic acid
H3C
2-Methyl-oxirane or Propylene Oxide or Propene Oxide
H
+
CH3CO3H
Peracetic acid
O
H
Cis-Cyclohexene Oxide
H2SO4 / 140°C
HO
+ H2O
OH
O
Pentane-1,5-diol
Tetrahydro-pyran
1,4-Dioxane
Reactions of epoxides
(three membered cycllic ethers)
H2O / H
Diol
OH
OH
CH3OH / H
Alkoxyalcohol
OCH3
O
OH
O
PhOH / H
OH Phenoxyalcohol
Ethylene oxide
HX / H
Haloalcohol
OH
X
1) RMgX
2) H3O
Bigger alcohol
R
OH
1) LiAlH4
2) H3O
H3C
OH
Ethanol
NH3
Aminoalcohol
NH2
OH