Problem 16 - A Complete Resource Book in Chemistry for JEE Main

Question

Diethyl ether is prepared by passing vapours of ethyl alcohol over a heated catalyst under high temperature and pressure. The catalyst is (a) \(\mathrm{CuO}\) (b) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{SiO}_{2}\) (d) \(\mathrm{Ag}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The catalyst is (b) Al2 O3 .

Step 1: Understand Diethyl Ether Formation

Diethyl ether is formed by the dehydration of ethyl alcohol (ethanol) in a chemical reaction where a catalyst is used to facilitate the process.

Step 2: Identify Correct Catalyst for Ether Formation

The etherification of ethanol involves a dehydration process where a common catalyst used is alumina ( Al2 O3 ) because it effectively aids in removing a water molecule from ethanol to form diethyl ether.

Step 3: Apply Knowledge of Reaction Conditions

Among the options given, Al2 O3 , known as aluminum oxide, is a standard catalyst used at high temperature and pressure in reactions that dehydrate alcohols to form ethers.

Key Concepts

Dehydration of Ethanol

The process of dehydration of ethanol is a crucial step in the preparation of diethyl ether. In simple terms, dehydration refers to the removal of a water molecule from a compound. In this context, ethanol, also known as ethyl alcohol, undergoes dehydration to form diethyl ether. This chemical transformation occurs when ethanol vapors are passed over a catalyst at elevated temperatures.
The reaction can be represented by the following chemical equation:

• C4H10O (diethyl ether)
  is produced by removing water from
  2 C2H5OH (ethanol).

Ethanol molecules lose a water molecule, resulting in the formation of an ether linkage between two ethanol molecules. This linkage is what forms diethyl ether in the process. The crucial aspect of this reaction is the removal of water (H₂O) to yield the final product, diethyl ether.

Catalyst in Organic Chemistry

Catalysts play an essential role in organic chemistry by accelerating or facilitating chemical reactions. They are substances that increase the rate of a chemical reaction without being consumed in the process. In organic reactions, catalysts can make reactions more efficient and can often lead to higher yields of the desired product.
Here are some key roles of catalysts in organic reactions:

• Catalysts lower the activation energy required for a reaction, allowing it to proceed at a faster rate even at lower temperatures.
• They enhance reaction specificity, often steering reactions toward one specific product over others.
• Catalysts often make the reaction pathway more straightforward, reducing the number of steps required for the conversion.

In the preparation of diethyl ether, a catalyst is crucial to facilitate the dehydration of ethanol and to ensure that it occurs efficiently. Without a catalyst, the reaction might require extreme conditions or may not proceed at all, making the catalyst indispensable.

Alumina as Catalyst

Alumina ( Al₂O₃ ), or aluminum oxide, is commonly used as a catalyst in organic reactions, particularly for dehydration processes. Its significance lies in its ability to effectively assist in the removal of water molecules, which is essential for the conversion of ethanol to diethyl ether.
There are several reasons why alumina is an ideal choice for catalyzing this reaction:

• Alumina has a high surface area, providing ample space for the reaction to take place, enhancing its effectiveness.
• It is stable at high temperatures, making it suitable for reactions requiring heat, such as the dehydration of ethanol.
• Alumina is a solid catalyst, making it easy to handle and separate from reaction mixtures.

In this specific reaction, heating ethanol in the presence of alumina allows for efficient dehydration, resulting in the formation of diethyl ether. The ability of alumina to act as a catalyst in this context is fundamental to the overall reaction success.