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) \(\mathrm{Al}_{2} \mathrm{O}_{3}\).

Step 1: Understand the Reaction

Diethyl ether is produced from ethyl alcohol (ethanol) by dehydration. In this process, ethanol molecules lose water to form diethyl ether.

Step 2: Recall the Catalyst

The dehydration of ethanol to form diethyl ether requires an acidic catalyst. The most common catalyst for such reactions is \[\mathrm{Al}_{2} \mathrm{O}_{3}\] which effectively facilitates the dehydration process at high temperatures.

Step 3: Identify the Correct Catalyst

From the given options, \[\mathrm{Al}_{2} \mathrm{O}_{3}\] is the only known catalyst used in the production of diethyl ether from ethanol vapours.

Key Concepts

Dehydration Reaction

A dehydration reaction is a chemical process where a water molecule is removed from the reactant molecule, leading to the formation of a new product. In the context of diethyl ether preparation, this reaction involves ethanol molecules. When ethanol undergoes dehydration, it loses a water molecule ( 711). This type of reaction is vital in organic chemistry because it allows for the transformation of simple alcohols into ethers and alkenes. Dehydration reactions often require a catalyst and specific conditions, such as elevated temperature and pressure, to proceed efficiently. The removal of water not only promotes the formation of the desired product but also shifts the equilibrium towards its production, as per Le Chatelier's principle.

Ethanol

Ethanol, commonly known as ethyl alcohol, is a simple alcohol with the chemical formula 711. It is a volatile, flammable, and colorless liquid that is widely used in the production of alcoholic beverages, as well as in industrial and laboratory settings. Ethanol's role in the preparation of diethyl ether is as a substrate. In the dehydration process, ethanol molecules are converted into diethyl ether with the removal of water. This transformation is significant because it exemplifies how simple alcohols can serve as building blocks for more complex organic compounds. Ethanol itself is widely produced by the fermentation of sugars or by the hydration of ethylene in the chemical industry.

Catalysis

Catalysis refers to the acceleration of a chemical reaction by a substance known as a catalyst, which remains unchanged by the overall process. In the dehydration of ethanol to make diethyl ether, catalysis is essential to enable the reaction to occur at a reasonable rate and under controlled conditions. Catalysts work by providing an alternative reaction pathway with a lower activation energy, facilitating the conversion of reactants into products. In this scenario, catalysts not only speed up the reaction but also help maintain the stability of the reaction environment. This stabilization allows for efficient production, minimizing energy inputs and maximizing yield.

Aluminum Oxide Catalyst

Aluminum oxide ( 711), also known as alumina, is a highly effective catalyst used in many chemical reactions, including the dehydration of ethanol to form diethyl ether. This catalyst has several characteristics that make it optimal for this process. It is non-volatile, has a high melting point, and provides an acidic surface that facilitates the removal of water from ethanol. The surface of aluminum oxide offers active sites where ethanol molecules can adsorb and undergo dehydration more readily. When ethanol vapors pass over heated aluminum oxide, the catalyst accelerates the reaction while remaining unchanged, allowing it to be used repeatedly. This makes aluminum oxide not only practical but also economical for industrial applications.