You have probably come across a variety of organic compounds in your organic chemistry section. So, we are quite confident that you know about the ether family. Do you know what ethers are? Do you know the various methods for preparation of ethers?
Well, if the answer to these questions is ‘No’, then you really need to go through this chapter once! We have created a brief summary for you to understand all about ethers and their methods of preparation. We will start with what ethers are.
What are Ethers?
Ethers are the organic compounds containing an oxygen atom bonded to two same or different alkyl or aryl groups. We can write the general formula for ethers as R-O-R, R-O-Ar or Ar-O-Ar. As we already know from the chapter of nomenclature, R represents an alkyl group and Ar represents an aryl group.
We can classify these into two categories on the basis of substituent group attached: symmetrical ethers and asymmetrical ethers. The former ether is when we have two identical groups attached to the oxygen atom. On the other hand, an asymmetrical ether is when we have two different groups attached to the oxygen atom.
Preparation of Ethers
These days, with the advancement in technology, we can synthesise ethers in industries in a number of ways. Let us now look at some of the most common industrial methods of preparation of ethers.
1) Preparation of Ethers by Dehydration of Alcohols
In the presence of protic acids (sulphuric acid), alcohols undergo dehydration to produce alkenes and ethers under different conditions. For example: in the presence of sulphuric acid, dehydration of ethanol at 443 K yields ethene. On the other hand, it yields ethoxyethane at 413 K. This is an ideal method of preparation for primary alcohols.
The preparation of ethers by dehydration of an alcohol is a nucleophilic substitution reaction. There are two major roles of the alcohol that we find in this reaction. One is that the alcohol molecule can act as the substrate while the other is that it acts as a nucleophile. It can follow either SN1 or SN2 mechanism.
The choice of mechanism is dependent on whether the protonated alcohol loses water before or simultaneously upon the attack of a second alcohol molecule. Generally, we will find that the secondary and tertiary alcohols follow SN1 mechanism. While on the other hand, the primary alcohols follow SN2 mechanism.
2) Preparations of Ethers by Williamson Synthesis
Williamson synthesis is an important method for the preparation of symmetrical and asymmetrical ethers in laboratories. In this method, we carry out a reaction of an alkyl halide with sodium alkoxide which leads to the formation of ether. The reaction generally follows SN2 mechanism for primary alcohol.
As we know alkoxides are strong bases and they can react with alkyl halides. Thus, they take part in elimination reactions. Williamson synthesis exhibits higher productivity in case of primary alkyl halides.
Solved Example for You
Q: Why do ethers have a dipole nature?
Ans: Ethers have a tetrahedral geometry i.e., oxygen is sp3 hybridized. The C— O—C angle in ethers is 110°. Due to the greater electronegativity of oxygen than carbon, the C—O bonds are slightly polar and are inclined to each other at an angle of 110° This is what results in ethers having a net dipole moment.