Ethers: Physical and Chemical Properties, Uses, Practice Problems and Frequently Asked Questions

We are all aware that the doctor will administer anaesthesia prior to performing any surgery.

Do you know what chemical is used in the administration of anaesthesia?

It is simply diethyl ether, which belongs to the ether family.

Ethers are mostly used in surgery as anaesthesia. Because ethers are volatile liquids, they emit vapours that patients inhale or administer intravenously. They cause patients to lose consciousness prior to surgery. For example, Diethyl ether is used as a strong anaesthetic, and its effects are aided by analgesics and muscle relaxation.

Because of their low toxicity and flammability, halogenated ethers such as isoflurane, desflurane, and others are now used as effective anaesthesia.

Halogenated ethers as isoflurane, desflurane, and others are now used as reliable anaesthetics due to their low toxicity and flammability.

Table of content:

• What is an ether?
• Physical properties of ethers
• Chemical properties of ethers
• Uses of ethers
• Practice problems
• Frequently asked questions

What is an ether?

An ether is a type of organic compound that mainly contains an ether group in which the oxygen atom is bonded to two alkyl or aryl groups, two aryl groups or two alkyl groups. The word Ether is derived from the Latin word "ether" which means "to burn". At room temperature and under high pressure, ethers are usually flammable. The general formula of the ether is given by ROR, ROR', ROAr or ArOAr where R represents an alkyl group and Ar represents an aryl group. R denotes an alkyl group, while Ar denotes an aryl group. 

We often come across this topic in organic chemistry and it is also a widely covered topic in biochemistry, where we find common bonds between carbohydrates and lignin. Whereas if we look at the structure of the ethers, they basically have bent C-O-C bonds.
 

Physical properties of ethers:

Physical State

Methoxy methane and methoxy ethane are gases, while other members are volatile liquids with a pleasant smell. Other lower homologues are colourless, pleasant-smelling, volatile liquids having an ether-like odour.

Methoxy ethane and methoxy methane are gases, while the remaining members have a pleasant smell and are volatile liquids. Pleasant smelling,colourless, volatile liquids with an ether-like odour are other lower homologues.

Polar nature of ethers

Ethers are polar substances. This is due to a difference in electronegativity between the oxygen and carbon atoms. Because of the electronegativity difference, the oxygen atom pulls the shared pair of electrons closer to itself, resulting in a partial negative charge on the oxygen atom and a partial positive charge on the carbon atom.

In the ether, two polar C–O bonds are inclined at an angle of 111.7 degrees to each other. As a result, the two dipoles do not cancel each other out, leaving a net dipole moment. In other words, the dipole moment () in ether ≠0.

Ethers are more polar than alkenes, but not as polar as alcohols, esters, or amides.

Ethers are polar compounds. This is because the oxygen and carbon atoms have different electronegativity. Because of the difference in electronegativity, the oxygen atom attracts the shared pair of electrons, resulting in a partial negative charge on the oxygen atom and a partial positive charge on the carbon atom.

Two polar C-O bonds in the ether are inclined at an angle of 111.7 degrees to each other. As a result, the two dipoles do not cancel out, resulting in a net dipole moment. To put it another way, the dipole moment () in ether ≠0

Ethers have a higher polarity than alkenes but not as high as alcohols, esters, or amides.

Boiling point of ethers:

Because ethers lack intramolecular hydrogen bonds, their boiling point is lower than that of isomeric alcohols, but closer to that of alkanes of comparable mass. Even though both (alcohol and ethers) have the same chemical formula C₂H₆O, but the boiling point of methoxy methane (CH₃OCH₃) is lower than that of ethanol (CH₃CH₂OH).

Ethers' boiling point is lower than that of isomeric alcohols but closer to that of alkanes of comparable mass because they do not have intramolecular hydrogen bonding. Although both alcohol and ethers have the same chemical formula C₂H₆O, methoxy methane (CH₃OCH₃) boiling point is lower than ethanol (CH₃CH₂OH).

Solubility of ethers:

In water, ethers with up to three carbon atoms are miscible. This is due to the ease with which lower ethers can establish hydrogen bonds with water molecules. Ethers are made up of the hydrophilic oxygen end, which is polar, and the hydrophobic hydrocarbon chain, which is non-polar.

With increasing alkyl group size, ether solubility in water decreases.This is due to the non-polar nature of the hydrocarbon component, which prevents hydrogen bonds from forming with the polar water molecules.

Ethers are relatively soluble in organic solvents including alcohols, benzene, and acetone.

For example, diethyl ether and n-butyl alcohol, have about the same solubility in water. This is due to the fact that ether, like alcohol, forms a hydrogen bond with water.

Ethers containing up to three carbon atoms are miscible in water. This is because lesser ethers may form hydrogen bonds with water molecules with great ease. Ethers are composed of a non-polar hydrophobic hydrocarbon chain and a polar hydrophilic oxygen end.

Ether solubility in water decreases with increasing alkyl group size.

This is because the hydrocarbon component is non-polar and prevents hydrogen bonds formation with the polar water molecules.

In organic solvents like acetone,benzene and alcohols, ethers are comparatively soluble.

For instance, the solubility of diethyl ether and n-butyl alcohol in water is almost the same. This is because ether and alcohol both create hydrogen bonds with water.

Chemical properties of ethers:

1. Combustion

Ethers are very flammable and produce carbon dioxide and water when they react explosively with air.

C₂H₅ O C₂H₅ + 6 O₂ → 4 CO₂ + 5 H₂O

2. Reaction with halogen acids: hydrogen halides

Ethers react with Conc. HBr or HI because these reagents are sufficiently acidic to protonate the ethers

Bromide and iodide are good nucleophiles for the substitution reaction. The order of reactivity is 

 HI > HBr >HCl

3. Electrophilic Substitution:

In the same manner as phenol activates the aromatic ring towards electrophilic substitution, the alkoxy group (-OR) is ortho, para directing and activates the ring towards electrophilic substitution reactions.

The ring is activated and directed toward electrophilic substitution reactions by the ortho, para-directing alkoxy group (-OR).

Halogenation

Bromination of anisole with bromine results in a mixture of ortho and para bromo anisole. It exemplifies the electrophilic aromatic substitution reaction. The bromine atom replaces the H atom attached to the benzene ring. Methoxy group is an ortho para directing group .

Friedel-Crafts Reaction:

The Friedel-Crafts reaction includes adding alkyl and acyl groups at ortho and para positions in anisole via reactions with an alkyl halide and an acyl halide in the presence of anhydrous aluminium chloride (a Lewis acid) as a catalyst.

Alkyl and acyl groups are added to anisole at the ortho and para positions through reactions with an alkyl halide and an acyl halide in the presence of anhydrous aluminium chloride (a Lewis acid) as a catalyst in the Friedel-Crafts reaction.

Uses of ethers:

Ethers are used for a variety of purposes, including the following:

• Ether is a solvent used to dissolve oil, resin, gasoline, gum, and other substances.

• Because of their nearly inert nature and high dissolving power, they are also used as a reaction medium in certain reactions, such as the preparation of Grignard reagent and their reactions and the Wurtz reaction.

• It is also used as an anaesthetic agent.

• It can also be used to keep things cool.

Ether is a solvent that can be used to dissolve gasoline, gum, oil,resin and other substances.

They are also utilised as a reaction medium in certain reactions, such as the manufacture of Grignard reagent and their reactions, and the Wurtz reaction, due to their nearly inert nature and high dissolving power.

It's also used as an anaesthetic.

It is also useful for keeping things cool.

Practice problems:

Q 1. Anisole on reaction with concentrated sulphuric acid and nitric acid gives 

(A) o-nitro anisole
(B) m-nitro anisole
(C) Both (A) & (B)
(D) None of these

Answer: (A)
When anisole reacts with concentrated sulphuric and nitric acids, ortho and para nitro anisole are formed. In these products para nitro anisole is the major product due to steric reasons.

Q 2. Diethyl ether on reaction with dilute sulphuric acid will give

(A) Ethanol
(B) Methanol
(C) Propanol
(D) None of these

Answer: (A)
Diethyl ether hydrolyzes into alcohol when it reacts with dilute sulphuric acid. The reaction is given below

C₂H₅-O-C₂H₅+ dil.H₂SO₄ → 2 C₂H₅OH

Q 3. The formula of phenoxy benzene

(A) C₆H₅-O-C₆H₅
(B) C₆H₅(CO)C₆H₅
(C) C₆H₆-O-C₆H₆
(D) None of these

Answer: (A)
The common name of phenoxy benzene is diphenyl ether and its formula is C₆H₅-O-C₆H₅ 

Q 4. Because of the risk of explosion, ethers are not distilled to dryness. This is because of the formation of:

(A) Oxides
(B) Peroxides 
(C) Alcohols
(D) Ketones

Answer: (B)
Ethers are not distilled to dryness for fear of explosion due to peroxide formation. Peroxides are highly explosive and extremely reactive. They have a lower volatility than Ethers.

Frequently asked questions:

Q 1. Why is ether kept in a bottle with iron wire?
Answer: In the presence of sunlight, ether reacts strongly with atmospheric oxygen, forming peroxide, which explodes on heating and causes a serious accident.

When ether is stored in a bottle with iron wire, oxygen reacts with the iron to form iron oxide, which prevents ether peroxide formation. As a result, ether is stored in a bottle with iron wire.

What is the purpose of storing ether in a bottle with iron wire?

Answer: In the presence of sunshine, ether strongly combines with air oxygen, forming peroxide, which bursts on heating and causes a major accident.

When ether is kept in a bottle with iron wire, oxygen combines with the iron to form iron oxide, preventing the formation of ether peroxide. As a result, ether is kept in a container wrapped in iron wire.

Q 2. Do ethers and alcohols have the same chemical properties?
Answer: No, ethers and alcohols do not have the same chemical properties. The presence of OH groups in alcohol that are absent in ether is the fundamental difference between these compounds. Because hydrogen bonds cannot be formed between ether molecules, this compound has a boiling point that is more than 80^o C lower than the corresponding alcohol.

Q 3. Are ethers and alcohols chemical properties same?
Answer: The chemical properties of ethers and alcohols are not the same. The presence of OH groups in alcohol that are not present in ether is the main difference between these molecules. Because ethers molecules cannot form hydrogen bonds between themselves, the boiling point of this chemical is more than 80^o C lower than that of the comparable alcohol.

Q 4. Is diethyl ether basic or acidic?
Answer: Diethyl ether is a strong Lewis base that reacts with many Lewis acids. The oxygen atom in a diethyl ether molecule acts as a base because it has two lone pairs of electrons available for coordination.

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

Q 6. Why are ethers less soluble than alcohols in water?
Answer: In ethers, oxygen is highly electronegative so it can form hydrogen bonds with water molecules similar to alcohol. But since there is no H on the O of the ether, they can only act as a hydrogen bond acceptor (unlike alcohols) and thus have lower solubility in water than alcohols with similar molecular weight.

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