Chemical Properties of Ethers: Have you heard about the organic compound ether? If yes, then you should be well aware that it has a general formula \({\rm{R – O – R’}}\) in which \({\rm{R}}\) and \({{\rm{R}}^\prime }\) may be the same. There are two types of ethers- aliphatic ethers and aromatic ethers. Ethers are polar in nature because the electronegativity of oxygen is greater than that of carbon.

Furthermore, because the two \({\rm{C – O}}\) bonds in the ether are inclined at an angle of \({110^ \circ }\), the two dipoles do not cancel each other, resulting in a net dipole moment. Ethers are used as anaesthetic agents as well as used to keep things cool. In this article, we will study some of the chemical properties of aliphatic and aromatic ethers.

Check Physical Properties of Ethers

What are Ethers?

Ethers are organic compounds that contain an oxygen atom attached to two alkyl or aryl groups, which can be the same or different. The general formula for ethers can be written as \({\rm{R – O – R,R – O – Ar,}}\) or \({\rm{Ar – O – Ar}}\). The organic nomenclature \({\rm{R}}\) represents an alkyl group, and \({\rm{Ar}}\) represents an aryl group in the above formula. These compounds can be divided into two types or categories. This classification is determined by the substituent groups attached to the compound. As a result, we can categorise them as-
1. The oxygen atom is attached to two identical groups in symmetrical ether.
2. The oxygen atom is attached to two different groups in asymmetrical ether.

Ethers exhibit various properties. We shall discuss some of the chemical properties of ethers in detail.

Chemical Properties of Ethers

Ethers are colourless, sweet-smelling liquids that are highly volatile and flammable. Because of H-bonding and hydrophobic alkyl or aryl groups, ethers are only sparingly soluble in water.

Ethers lack hydrogen bonding within themselves. Therefore, their boiling points are much lower than those of corresponding alcohols.

Diethyl ether vapours induce unconsciousness upon inhalation and are thus used as an anaesthetic agent.

Ethers have a bond angle of \({\rm{C – O – C}}\) of about \({110^ \circ }\), and thus the dipole moments of two \({\rm{C}} – {\rm{O}}\) bonds do not cancel out. Thus, ethers are polar but have weak polarity (for diethyl ether \( = 1.18\,{\rm{D}}\)).

Ethers have a lower reactivity than compound functional groups. They are not affected by active metals, strong bases, or reducing and oxidising agents. The chemical properties of ethers are due to the presence of an alkyl group, a lone pair of electrons on the oxygen atom, and the cleavage of the \({\rm{C}} – {\rm{O}}\) bond.

Reactions Due to Alkyl Group

Combustion

Ethers are highly flammable and combine explosively with air to produce carbon dioxide and water.
\({{\rm{C}}_2}{{\rm{H}}_5}{\rm{O}}{{\rm{C}}_2}{{\rm{H}}_5} + 6{{\rm{O}}_2} \to 4{\rm{C}}{{\rm{O}}_2} + 5{{\rm{H}}_2}{\rm{O}}\)

Halogenation

In the absence of sunlight, the alkyl group of ether undergoes a substitution reaction with chlorine or bromine to produce a-halogenated ethers.

In the presence of sunlight, however, all of the hydrogen atoms in ethers are substituted.

Reaction Due to Ethereal Oxygen

Peroxide Formation

Due to the presence of lone pair of electrons on the ethereal oxygen, when ether comes into contact with atmospheric oxygen in the presence of sunlight, it reacts with oxygen to form ether peroxide. Ether peroxide is highly unstable and explodes violently when heated, resulting in serious accidents. As a result, boiling a sample of ether that has been stored for an extended period of time is risky.

Formation of Oxonium Salts

Since ethers can behave as weak Lewis bases, they can dissolve in cold and concentrated mineral acids such as hydrochloric acid or sulphuric acid to form oxonium salts. (That is, protonation by the acid).

Reactions Involving Cleavage of C-O Bond

Reaction with Halogen Acids (HX)

When ethers are heated with concentrated halogen acids (particularly \({\rm{HI}}\) and \({\rm{HBr}}\)), the \({\rm{C-O}}\) bond is cleaved, yielding alcohol and alkyl halide.

When it comes to unsymmetrical ethers, the larger alkyl group forms alkyl iodide, and the smaller alkyl group forms alcohol.
The order of reactivity is as follows-

\({\rm{HI}} > {\rm{HBr}} > {\rm{HCl}}\)

Cleavage occurs only under extreme conditions: concentrated acids (typically \({\rm{HI}}\) or \({\rm{HBr}}\)) and high temperatures.

Hydrolysis

Ether forms alcohol on acidic hydrolysis.

Reaction with \({\rm{PC}}{{\rm{l}}_{\rm{5}}}\)

When ether is heated with \({\rm{PC}}{{\rm{l}}_{\rm{5}}}\), the \({\rm{C-O}}\) bonds in the ether are cleaved, resulting in the formation of alkyl chloride.

Reactions in Aromatic Ethers

Electrophilic Substitution

In the same way that phenol does, the alkoxy group \(( – {\rm{OR}})\) is ortho, para directing and activates the aromatic ring towards electrophilic substitution.

II, III, and IV demonstrate a high electron density in the ortho and para positions.

Halogenation

Phenyl Alkyl ethers undergo typical halogenation in the benzene ring. For example, anisole undergoes bromination with bromine in ethanoic acid even in the absence of an iron (III) bromide catalyst. It is caused by the methoxy group activating the benzene ring. \({\rm{90 \% }}\) of the time, the para isomer is obtained as a major product.

Friedel-Crafts Reaction

Anisole undergoes the Friedel-Crafts reaction, which involves introducing alkyl and acyl groups at ortho and para positions via reactions with an alkyl halide and acyl halide in the presence of anhydrous aluminium chloride (a Lewis acid) as a catalyst.

Nitration

Anisole reacts with concentrated sulphuric and nitric acids to produce ortho and para nitro anisole.

Uses of Ethers

Some of the uses of Ethers are as follows-
i. Ether is a solvent that is used to dissolve oil, resin, gasoline, gum, and other substances.
ii. Because of their almost inert nature and high dissolving power, they are also used as a reaction medium for certain reactions, for example, in the preparation of Grignard reagent, the Wurtz reaction, and so on.
iii. It is also employed as an anaesthetic agent.
iv. It is also used to keep things cool.

Summary

We can conclude that an oxygen atom is linked to two alkyl or aryl groups in ethers. \({\rm{R}} – {\rm{O}} – {{\rm{R}}^\prime }\) is the general formula for ether. We also studied that ethers, in general, are very unreactive in nature. The \({\rm{C-O}}\) bond is cleaved when an excess of hydrogen halide is added to the ether. Alkyl halides are formed as a result. Now we know that the alkoxy group of the ether activates the aromatic ring at the para and ortho positions for electrophilic substitution. Friedel Crafts reaction, halogenation, and a few others are examples of common electrophilic substitution reactions. We also studied some of the uses of ethers.

FAQs

Q.1. Why is ether stored in a bottle containing iron wire?
Ans: In the presence of sunlight, ether is highly reactive to atmospheric oxygen, forming peroxide, which explodes on heating, causing a serious accident.
When ether is stored in a bottle with iron wire, oxygen combines with the iron to form iron oxide, preventing peroxide formation of ether. As a result, ether is kept in a bottle containing iron wire.

Q.2. What are the uses of diethyl ether?
Ans: Some of the uses of diethyl ether are as follows-
i. It is primarily used as a solvent for oils, fats, gums, resins, plastics, and other similar substances.
ii. It serves as a refrigerant.
iii. In surgery, it is used as a general anaesthetic agent.
iv. It is mixed with alcohol and used as a petrol substitute under the brand name Natalite.

Q.3. Are the chemical properties of ethers and alcohols the same?
Ans: No, the chemical properties of ethers and alcohols are not the same. This is because the presence of \({\rm{OH}}\) groups in the alcohol that are absent in the ether is the fundamental difference between these compounds. Because hydrogen bonds cannot form between ether molecules, the boiling point of this compound is more than \(80\) degrees Celsius lower than that of the corresponding alcohol.

Q.4. What are the physical properties of ethers?
Ans: The physical properties of ethers are as follows:
i. A net dipole moment exists in an ether molecule. This is due to the polarity of the \({\rm{C-O}}\) bond.
ii. The boiling point of ether is comparable to that of alkanes.
iii. The miscibility of ether with water is similar to that of alcohol.
iv. Ether molecules are miscible in water.

Q.5. Is diethyl ether acidic or basic?
Ans: Diethyl ether is a strong Lewis base that reacts with a wide range of Lewis acids. Because the oxygen atom in a diethyl ether molecule has two lone pairs of electrons available for coordination, it behaves as a base.