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Physical and Chemical Properties of Ethers

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  • Last Updated : 28 Apr, 2022

Organic chemicals such as alcohol, phenol, and ether are extensively employed in both domestic and industrial settings. Perfumes, sanitizers, and fuels are all examples of these goods, which are used in a number of ways in our daily lives.

What are Ethers?

Ethers are a form of an organic molecule in which a single oxygen atom connects two hydrocarbon groups (alkyl or aryl). It is represented using the R-O-R′ formula.

 

In the formula, R′, the hydrocarbon group could be the same as or different from R.

Ethers are generated when the hydrogen atom of the hydroxyl group in alcohols is replaced by an alkyl or aryl group.

For example-

 

The oxygen and carbon in the C-O-C bond are sp3 hybridized. The repulsion of two lone pairs (lp) on the oxygen atom causes the bending form. The presence of bulky groups at both ends of the oxygen atom, as well as the bp-bp repulsion resulting in a C-O-C bond angle of around 111.7, produce a steric barrier.

 

Classification of Ethers

Ethers are divided into two types based on the groups at R and R’:

  • Simple ethers or symmetrical ethers: These ethers have the same alkyl group on both ends of the oxygen atom. For example,

 

 

  • Mixed ethers or asymmetrical ethers: These ethers are made up of different alkyl groups on both ends of the oxygen atom. For example,

Ethyl Methyl Ether

Methyl Phenyl Ether

Physical Properties of Ethers

The physical characteristics of ethers are as follows:

  • Physical State: Other ingredients are odourless volatile liquids, while methoxy methane and methoxy ethane are gases. Lower homologues include colourless, pleasant-smelling, volatile liquids having a characteristic ether odour.
  • Polar Nature of Ether: Ethers have a polar character. The difference in electronegativity between the oxygen and carbon atoms is the reason behind this. The oxygen atom pushes the shared pair of electrons closer to itself due to the electronegativity difference, 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 one another. As a result, the two dipoles do not cancel out, resulting in a net dipole moment. i.e., in ether, the dipole moment (μ) ≠ 0. Ethers are more polar than alkenes but not as polar as alcohols, esters, or amides with similar structures.
  • Hydrogen Bonding of Ether: The hydrogen atom is not directly bound to the oxygen atom in ethers. As a result, ethers contain no hydrogen bonds between molecules. Ethers, on the other hand, are only used to accept hydrogen bonds. Hydrogen bonding with water molecules is feasible because oxygen atoms have two lone pairs of electrons.

 

When compared to linear aliphatic ethers, cyclic ethers such as tetrahydrofuran and 1,4-dioxane are miscible in water due to the more exposed oxygen atom for hydrogen bonding.

  • Boiling Point of Ether: Because ethers do not establish intramolecular hydrogen bonds, their boiling temperature is lower than that of isomeric alcohols, but it is closer to that of alkanes of the same mass. Even though both have the same chemical formula C2H6O, the boiling point of methoxy methane (CH3OCH3) is lower than that of ethanol (CH3CH2OH).
  • Solubility of Ether: Ethers with up to three carbon atoms are miscible in water. This is because lesser ethers have an easier time forming hydrogen bonds with water molecules. Ethers are made up of two types of molecules: the nonpolar hydrophobic hydrocarbon chain and the polar hydrophilic oxygen end. The solubility of ether in water decreases as the size of the alkyl group increases. This is owing to the hydrocarbon component’s non-polar nature, which inhibits hydrogen bonds with the polar water molecules from forming. Organic solvents such as alcohols, benzene, and acetone are relatively soluble in ethers. Diethyl ether and n-butyl alcohol, for example, are water-soluble to a similar extent. Because ether forms a hydrogen connection with water in the same way as alcohol does.
  • Acidity: Water, ethers, and alcohols all have similar oxygen bonds. Because oxygen is more electronegative than carbon, the hydrogens alpha to ethers in simple hydrocarbons is more acidic. They are far less acidic than the alpha to carbonyl groups of hydrogen (such as in ketones or aldehydes).
  • Ethers are lighter than water.

Chemical Properties of Ethers

  • Ethers are colorless, sweet-smelling, extremely volatile, and combustible liquids. Ethers are only sparsely soluble in water due to H-bonding and hydrophobic alkyl or aryl groups.
  • Within themselves, ethers do not have hydrogen bonds. As a result, their boiling points are significantly lower than the boiling points of equivalent alcohols.
  • Diethyl ether vapors are employed as an anesthetic because they produce unconsciousness when inhaled.
  • Because ethers have a C–O–C bond angle of around 110, the dipole moments of two C–O bonds do not cancel out. As a result, ethers are polar, but their polarity is weak (for diethyl ether =1.18D).
  • The reactivity of ethers is lower than that of complex functional groups. Active metals, strong bases, and reducing and oxidizing agents have no effect on them. The presence of an alkyl group, a lone pair of electrons on the oxygen atom, and the breakage of the C–O bond give ethers their chemical characteristics.

Reactions Due to Alkyl Group

  • Combustion: Ethers are extremely combustible, and when they come into contact with air, they form carbon dioxide and water.

C2H5OC2H5 + 6O2  →  4CO2 + 5H2O

  • Halogenation: The alkyl group of ether undergoes a substitution process with chlorine or bromine in the absence of sunlight, resulting in a-halogenated ethers.

 

All of the hydrogen atoms in ethers are substituted in the presence of sunlight.

Reaction Due to Ethereal Oxygen

  • Peroxide Formation: When ether comes into touch with atmospheric oxygen in the presence of sunlight, it interacts with oxygen to generate ether peroxide due to the presence of a lone pair of electrons on the ethereal oxygen. When heated, ether peroxide is highly unstable and explodes violently, causing serious accidents. As a result, boiling an ether sample that has been held for a long time is dangerous.

 

  • Formation of Oxonium Salts: Because ethers can act as weak Lewis bases, they can create oxonium salts when dissolved in cold, strong mineral acids like hydrochloric or sulphuric acid.

 

Reactions in Aromatic Ethers

  • Halogenation: In the benzene ring, phenyl alkyl ethers undergo normal halogenation. Even in the absence of an iron (III) bromide catalyst, anisole conducts bromination with bromine in ethanoic acid. The methoxy group activates the benzene ring, resulting in this reaction. The para isomer is obtained as the main product 90% of the time.

 

  • Friedel-Crafts Reaction: The Friedel-Crafts process 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. 

 

  • Nitration: Ortho and para nitro anisole are formed when anisole interacts with strong sulphuric and nitric acids.

 

Uses of Ethers

  1. Ether is a solvent for dissolving oil, resin, gasoline, gum, and other materials.
  2. Due to their practically inert nature and high dissolving power, they are also used as a reaction media for several procedures, such as the synthesis of Grignard reagent, the Wurtz reaction, and so on.
  3. It also serves as a local anesthetic.
  4. It’s also used to maintain a cool environment.

Sample Questions

Question 1: What is the classification of ether?

Answer:

Ethers are divided into two categories based on the presence of a hydrocarbon (aryl or alkyl) chain at both ends of the oxygen atom: simple or symmetrical ethers, and mixed or asymmetrical ethers.

  • Simple or symmetrical ethers are created when the hydrocarbon (aryl or alkyl) chain present at both ends of the oxygen atom is the same. CH3OCH3 is an example.
  • Mixed or asymmetrical ethers are created when the hydrocarbon (aryl or alkyl) chain present at both ends of the oxygen atom is different. -CH3OC2H5 is an example.
     

Question 2: Why are ethers soluble in water?

Answer:

Two alkyl groups (R–O–R′) are connected to the ends of an oxygen atom in ethers. Because of its high electronegativity, oxygen behaves as a hydrogen-bond acceptor and is soluble in water in the same way that alcohols are.

Question 3: How to convert alcohol into the ether?

Answer:

The production of ethers is caused by the acid catalysed dehydration of primary alcohols. A condensation reaction occurs when two molecules of primary alcohol combine to generate a bigger one while also freeing a tiny molecule of water.

Question 4: Why is ether stored in a bottle containing iron wire?

Answer:

When exposed to sunlight, ether reacts strongly with ambient oxygen, creating peroxide, which explodes when heated, resulting in a major accident.

When ether is held in a bottle with iron wire, oxygen reacts with the iron to generate iron oxide, which prevents ether from becoming peroxide. As a result, ether is stored in a container with iron wire inside.

Question 5: What is diethyl ether used for?

Answer:

  1. Oils, fats, gums, resins, polymers, and other similar compounds are mostly dissolved in it.
  2. It performs the function of a refrigerant.
  3. It is used as a general anaesthetic in surgery.
  4. Under the brand name Natalite, it is combined with alcohol and used as a fuel alternative.

Question 6: What are the physical properties of ethers?

Answer:

  1. In an ether molecule, there is a net dipole moment. This is due to the polarity of the C−O bond.
  2. Ether has a boiling point similar to that of alkanes.
  3. Ether is miscible with water in the same way as alcohol is.
  4. In water, ether molecules are miscible.

Question 7: What is Friedel-Crafts Reaction?

Answer:

The Friedel-Crafts procedure involves reacting an alkyl halide and an acyl halide in the presence of anhydrous aluminium chloride (a Lewis acid) to add alkyl and acyl groups at ortho and para positions in anisole.

 


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