Problem 58 - A Complete Resource Book in Chemistry for JEE Main

Question

When diethyl ether is treated with an excess of \(\mathrm{Cl}_{2}\) in the presence of sunlight, the product formed is (a) \(\mathrm{CH}_{3} \mathrm{CHCl}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{CHCl}-\mathrm{O}-\mathrm{CHClCH}_{3}\) (c) \(\mathrm{CCl}_{3} \mathrm{CCl}_{2}-\mathrm{O}-\mathrm{CCl}_{2} \mathrm{CCl}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{CCl}_{2}-\mathrm{O}-\mathrm{CHClCH}_{3}\)

Step-by-Step Solution

Answer

Option (c) is the product formed: \(\mathrm{CCl}_3\mathrm{CCl}_2\)-O-\(\mathrm{CCl}_2\mathrm{CCl}_3\).

Step 1: Understanding the Reaction

Diethyl ether (\(\mathrm{C}_2\mathrm{H}_5\)-O-\(\mathrm{C}_2\mathrm{H}_5\)) is subjected to chlorination, which involves replacing hydrogen atoms with chlorine atoms. Excess \(\mathrm{Cl}_2\) means that the chlorination will continue as much as possible.

Step 2: Grasp the Nature of Chlorination

In the presence of sunlight, chlorination proceeds through a radical mechanism, meaning that all hydrogen atoms, wherever possible, will eventually be replaced with chlorine atoms due to the presence of excess \(\mathrm{Cl}_2\). This process is more aggressive for tertiary \(\mathrm{C}_3\) hydrogens, but given excess chlorine, all hydrogens will be replaced eventually.

Step 3: Applying Excess Condition

Since there is an excess of chlorine, every hydrogen atom in diethyl ether will be replaced by a chlorine atom. Therefore, both \(\mathrm{CH}_3\) groups of diethyl ether will be fully chlorinated.

Step 4: Recognizing the Product

The complete chlorination of diethyl ether results in \(\mathrm{CCl}_3\mathrm{CCl}_2\)-O-\(\mathrm{CCl}_2\mathrm{CCl}_3\), as every hydrogen on the carbon chains is replaced by chlorine.

Key Concepts

Diethyl Ether

Diethyl ether is an organic compound widely known for its use as a solvent in laboratories and in the preparation of certain pharmaceuticals. Structurally, it consists of two ethyl groups (\(\mathrm{C}_2\mathrm{H}_5\)) connected by an oxygen atom, resulting in the formula \(\mathrm{C}_2\mathrm{H}_5\)-O-\(\mathrm{C}_2\mathrm{H}_5\).

When it comes to its interaction with chemicals like chlorine, its simple structure provides several hydrogen atoms which can be replaced by other atoms or groups under certain chemical reactions, such as chlorination.

Due to its ether bond, diethyl ether is quite stable under normal conditions but can undergo aggressive reactions in the presence of reactive species like chlorine, especially when the reaction conditions are enhanced by light or heat.

Radical Mechanism

A radical mechanism is a chemical process that involves free radicals, which are atoms, molecules, or ions with unpaired electrons. This type of mechanism often occurs in reactions involving halogens, such as chlorine.

In the context of chlorination, when light is present, \(\mathrm{Cl}_2\) molecules are split into chlorine radicals. These radicals are extremely reactive and will initiate a chain reaction where a hydrogen atom from diethyl ether is replaced by a chlorine atom, forming new radicals in the process.

The radical chain mechanism often consists of three steps:

• Initiation: Light energy splits a \(\mathrm{Cl}_2\) molecule into two chlorine radicals.
• Propagation: Chlorine radicals react with diethyl ether, forming hydrochloric acid and a new ether radical. This ether radical then reacts with another \(\mathrm{Cl}_2\) molecule, continuing the chain sequence.
• Termination: The reaction proceeds until all hydrogen atoms are replaced or until the radicals are neutralized by recombination.

Understanding radical mechanisms is important as it illustrates the complexity of reactions and how even simple compounds like diethyl ether can be altered.

Excess Chlorine

Excess chlorine refers to the presence of more chlorine than is necessary to react with all available hydrogen atoms in a compound. In the chlorination of diethyl ether, excess chlorine ensures that every possible hydrogen atom is substituted by a chlorine atom.

Having an abundance of chlorine drives the reaction to not only initiate strong radical mechanisms but also allows it to continue until saturation is achieved – replacing hydrogens with chlorines on all available sites on diethyl ether.

• This results in a fully chlorinated product because each carbon atom in diethyl ether exchanges its hydrogen atoms for chlorine, creating a \(\mathrm{CCl}_3\) group on each end of the molecule.


• Using excess chlorine in reactions highlights how reactant concentrations can influence the pathway and completion of chemical processes, especially those involving radical mechanisms.

Organic Chemistry

Organic chemistry is the branch of chemistry that deals with the structure, properties, and reactions of organic compounds and materials. These compounds typically contain carbon atoms, especially bonded with hydrogen, as seen in hydrocarbons and their derivatives like ethers.

Chlorination of diethyl ether is an example of an organic reaction whereby substitution occurs. Organic chemistry provides us with the tools to understand how and why these reactions occur.

• It examines how reaction conditions such as light, heat, presence of catalysts, and concentration of reactants (such as excess chlorine) influence the reaction rates and outcomes.


• In essence, organic chemistry investigates the foundational principles that allow chemists to predict how molecules behave and how they can be transformed under different conditions, which is crucial for designing synthetic pathways and industrial processes.

Understanding organic chemistry is critical for explaining reactions like the chlorination of diethyl ether, especially when considering factors like radical mechanisms and reagent conditions.