Problem 93 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{CH}_{2}=\mathrm{CH}_{2} \frac{\mathrm{X}}{\mathrm{Ag}} \rightarrow \mathrm{X} \frac{\text { steam }}{473 \mathrm{~K}}-\mathrm{Y}\) The compound \(\mathrm{Y}\) is (a) ethylene glycol (b) epoxyethane (c) ethanal (d) ethanol

Step-by-Step Solution

Answer

The compound Y is (d) ethanol.

Step 1: Identify the Reaction Type

The given reaction involves the conversion of ethylene (\( \mathrm{CH}_{2}=\mathrm{CH}_{2} \)) in the presence of a catalyst, indicated as \( \mathrm{X/Ag} \), and under specific conditions with steam at \( 473 \mathrm{~K} \). This suggests a hydration reaction in the presence of a catalyst.

Step 2: Recall the Hydrolysis of Ethylene

In general, when ethylene is passed over a catalyst like silver (Ag) with steam, it typically leads to the formation of ethanol (\( \mathrm{C}_2\mathrm{H}_5\mathrm{OH} \)), due to the addition of water across the double bond of ethylene.

Step 3: Analyze Possible Reaction Products

The options provided include ethanol, ethylene glycol, epoxyethane, and ethanal. Given the context of the reaction involving hydration, ethanol is the most likely product as it involves the simple addition of \( \mathrm{H}_2\mathrm{O} \) across the ethylene double bond.

Key Concepts

Hydration Reaction

A hydration reaction is a chemical process where a water molecule is added to a substrate. In organic chemistry, this often occurs in the context of alkenes, like ethylene, where water is added across a double bond. This type of reaction is crucial in converting unsaturated hydrocarbons into alcohols, a transformation that has significant industrial and chemical importance. The overall process typically involves an alkene and a catalyst that facilitates the addition of water, where the hydrogen from water adds to one carbon of the alkene, and the hydroxyl group adds to the other.

• Water breaks the double bond.
• Forms an alcohol.

The effectiveness of a hydration reaction often depends on factors like temperature, pressure, and the presence of catalysts, ensuring that the reaction proceeds under favorable conditions.

Catalyst

A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. In the context of hydration reactions, a catalyst is essential as it provides an alternative pathway with a lower activation energy. This means the reaction can occur more readily and more efficiently. In the given exercise, silver (Ag) acts as the catalyst. It is particularly useful in facilitating the hydration of ethylene to produce ethanol.

• Reduces energy required for reaction.
• Increases reaction rate.
• Remains unchanged at the end.

Catalysts like silver not only accelerate the reaction but also ensure it happens at a commercially viable rate and temperature.

Ethylene

Ethylene (\(\mathrm{CH}_2=\mathrm{CH}_2\)) is a simple alkene, characterized by its double bond. It is one of the most fundamental building blocks in organic chemistry with widespread use in producing plastics and chemicals. Ethylene's double bond makes it highly reactive, especially in the presence of catalysts, which can facilitate various addition reactions.

• Basic structure leads to reactivity.
• Key component in synthetic industries.

In a hydration reaction, ethylene acts as the starting material, which upon reaction with water results in the formation of ethanol, a crucial step in many manufacturing processes.

Ethanol Production

Ethanol is a type of alcohol commonly used as a fuel, solvent, and disinfectant. The production of ethanol from ethylene involves a hydration reaction, where water is added to ethylene in the presence of a catalyst under controlled conditions. This process is especially significant because it allows for the transformation of simple hydrocarbons into more complex and usable compounds.

• Economic value as a fuel source.
• Applications in industrial and pharmaceutical products.

By utilizing ethylene, an abundantly available raw material, ethanol production not only serves numerous industrial applications but also supports sustainability and energy efficiency.