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

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 CH 3 OCH 3 and diethyl ether CH 3 — CH 2 — O — CH 2 — CH 3 . Mixed or unsymmetrical ethers, which contain different alkyl or phenyl groups, e.g., ethyl methyl ether CH 3 — O — CH 2 — CH 3 .

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 CH 3 OCH 3 Dimethyl ether Methoxy methane CH 3 OC 2 H 5 Methyl ethylether Methoxy ethane C 2 H 5 OC 2 H 5 Diethyl ether Ethoxy ethane C 2 H 5 O CH 2 — CH 2 — CH 3 Ethyl n-propylether Ethoxy propane CH 3 OC 6 H 5 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 . Williamsons synthesis Alkyl halides are heated with dry silver oxide to form ethers 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 E thers 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.

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