Ethers - INTRODUCTION, NOMENCLATURE, PREPARATION. PROPERTIES AND CHEMICAL REACTIVITY FSc. 2ND YEAR CHEMISTRY

1. Ethers
Introduction and Preparation
Humna Mehmood
BS Chemistry (2017-2021)
GPCSF

2. What are ethers?
Ethers are a class of organic compounds that contain an ether group—
an oxygen atom connected to two alkyl or aryl groups.
They have the general formula R–O–R′, where R and R′ represent the alkyl
or aryl groups.

3. Water derivatives
• Alcohols, phenols and ethers are classes of organic compounds which are
much closer to water in structure and hence considered as derivatives of
water.
• In ether both hydrogens of water are replaced by alkyl or phenyl groups.

4. Classification
Ethers are classified into two categories:
• Simple or symmetrical ethers, which contain two same alkyl groups e.g.
dimethyl ether CH3OCH3 and diethyl ether CH3— CH2— O — CH2 — CH3.
• Mixed or unsymmetrical ethers, which contain different alkyl or phenyl
groups, e.g., ethyl methyl ether CH3— O — CH2 — CH3.

5. Nomenclature
Ethers are named either by
I.U.P.A.C. system
common names

6. I.U.P.A.C. system
• In I.U.P.A.C. system the large alkyl (R ) group is taken as parent molecule
and given the last name (suffix) while the smaller alkyl group along with
oxygen is used as prefix and given the name alkoxy (e.g.methoxy, ethoxy,
propoxy, etc).

7. Common Names
• The most common way is to identify the alkyl groups on either side of the
oxygen atom in alphabetical order, then write “ether”.
• For example, ethyl methyl ether is the ether that has an ethyl group and a
methyl group on either side of the oxygen atom.
• If the two alkyl groups are identical, the ether is called di[alkyl] ether. For
example, diethyl ether is the ether with an ethyl group on each side of the
oxygen atom.

8. Nomenclature
• I. U.P. A. C. names are not common as they are difficult. Usually ethers are
known by their common names, as given below;
Formula Common Names I.U.P.A.C
CH3OCH3 Dimethyl ether Methoxy methane
CH3OC2H5 Methyl ethylether Methoxy ethane
C2H5OC2H5 Diethyl ether Ethoxy ethane
C2H5O CH2 — CH2 — CH3 Ethyl n-propylether Ethoxy propane
CH3OC6H5 Methyl phenyl ether Methoxy benzene

9. Preparation of Ethers
Ethers are prepared from alcohols either directly or indirectly. Usually they
are obtained by the following methods.
1. Williamsons synthesis
2. Alkyl halides are heated with dry silver oxide to form ethers
3. Bimolecular dehydration

10. 1. Williamsons synthesis
The most versatile method for making ethers is the
Williamson ether synthesis, named for English chemist Alexander
Williamson, who devised the method in the 19th century.
Alcohols are reacted with metallic sodium to form alkoxides. This alkoxide
ion is a strong nucleophile and readily reacts with alkyl halide to produce an
ether.

11. 2. Alkyl halides are heated with dry silver oxide to form ethers
Alkyl halides are heated with dry silver oxide to form ethers.

12. 3. Bimolecular dehydration
• In the presence of acid, two molecules of an alcohol may lose water to form
an ether.
• Bimolecular dehydration produces useful yields of ethers only with simple,
primary alkyl groups such as those in dimethyl ether and diethyl ether.
Dehydration is used commercially to produce diethyl ether.
• Examples:

13. Physical Properties
• Usually ethers are volatile liquids, highly inflammable with low boiling
points.
• They are slightly soluble in water but freely soluble in organic solvents.
• Ether molecules do not show hydrogen bonding with one another but they
show weak hydrogen bonding with water molecules due to which they are
slightly soluble in water.

14. Chemical Reactivity
Ethers are comparatively inert substances.
The reagents like ammonia, alkalies, dilute acids and metallic sodium, have
no action on ethers in cold state.
Moreover, they are not oxidized or reduced easily.

15. Chemical Reactivity
Ethers show some reactions, e.g.
1. With hydrogen iodide ethers give alcohols which can react further to give
alkyl iodides.
2. Ethers also react with hot phosphorus pentachloride to give alkyl chloride.

16. Chemical Reactivity
3. Cleavage
Ethers are good solvents partly because they are not very reactive. Most
ethers can be cleaved, however, by hydrobromic acid (HBr) to give alkyl
bromides or by hydroiodic acid (HI) to give alkyl iodides.