Problem 125 - A Complete Resource Book in Chemistry for JEE Main

Question

In the following reaction, \(\mathrm{X}\) is and \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5}+4 \mathrm{H} \stackrel{\operatorname{Red} \mathrm{P}+\mathrm{HI}}{\longrightarrow} 2 \mathrm{X}+\mathrm{H}_{2} \mathrm{O}\) (a) ethylene (b) propane (c) ethane (d) butane

Step-by-Step Solution

Answer

The compound \(X\) is ethane, option (c).

Step 1: Analyze the Reaction

The given reaction involves ethyl ether \((C_2H_5OC_2H_5)\) reacting with 4 molecules of hydrogen in the presence of red phosphorus and hydrogen iodide. The reaction produces compound \(X\) and water \((H_2O)\).

Step 2: Write the Reaction Equation

The reaction is given as: \[ C_2H_5OC_2H_5 + 4HI \rightarrow 2X + H_2O \]. In this reaction, \(C_2H_5\) groups are present which, when reduced, typically form ethane.

Step 3: Identify the Compound X

We know one molecule of ethyl ether \(C_2H_5OC_2H_5\) can be reduced to produce two \(C_2H_6\) molecules (ethane) upon treatment with HI. This is because HI helps cleave the oxygen and adds hydrogen to each of the ethyl groups, forming ethane.

Step 4: Choose from the Given Options

The options provided are (a) ethylene, (b) propane, (c) ethane, and (d) butane. Based on the steps above, the reaction produces ethane. Thus, \(X\) must be ethane.

Key Concepts

Reduction Reactions

Reduction reactions involve the gain of hydrogen or electrons, which often results in the decrease of oxygen content in a compound. In organic chemistry, reduction typically refers to the addition of hydrogen atoms to a molecule. In this process, the molecule is transformed to a more reduced state.
For example:

• Conversion of an alkene to an alkane.
• Reduction of a carbonyl group to an alcohol.

In the exercise described, ethyl ether undergoes a reduction reaction when reacting with hydrogen iodide (HI) and red phosphorus. Here, HI acts as a reducing agent facilitating the conversion of ethyl ether into ethane. This transformation is a classic example of how reduction reactions contribute to organic synthesis by breaking bonds and adding hydrogen molecules to the original compound.

Ethyl Ether

Ethyl ether, also known as diethyl ether, is a common organic compound with the formula \(C_2H_5OC_2H_5\). It is highly flammable and was historically used as an anesthetic. In the field of chemistry, it is often used as a solvent due to its non-polar characteristics.
When ethyl ether is subjected to reduction reactions, it undergoes significant molecular changes. In the presence of HI, the ether can be cleaved into two ethyl groups, each receiving an additional hydrogen atom.
This property makes diethyl ether a useful starting material for preparing other organic compounds through reduction. In the given exercise, ethyl ether is key to producing ethane by providing the necessary carbon framework that, upon reduction, leads to alkane formation.

Hydrogen Iodide (HI)

Hydrogen iodide (HI) is a diatomic molecule used widely in organic chemistry as a reducing agent. It is known for its ability to efficiently donate hydrogen atoms in reactions, allowing for reduction processes to occur.
In the described problem, HI plays a crucial role in breaking the oxygen linkage in ethyl ether, allowing hydrogen atoms to add to the resulting fragments.

• HI cleaves the ether bond, releasing water (\(H_2O\)) as one of the products.
• Red phosphorus is often used alongside HI to help regenerate the HI in situ, enhancing the effectiveness of the reduction process and ensuring that the reaction proceeds smoothly.

This effective combination of HI and red phosphorus underlies many important organic synthesis processes, optimizing the reduction of ethers and other similar compounds.

Alkane Formation

Alkane formation through reduction is a fundamental transformation in organic chemistry. Alkanes are saturated hydrocarbons, which means they contain only single bonds between carbon atoms, making them relatively stable.
In this exercise, the target product, ethane (\(C_2H_6\)), is formed from ethyl ether through reduction. This transformation involves the breaking of the ether bond and the addition of hydrogen atoms to the carbon chain, sequentially saturating it.

• The conversion from ethyl ether to ethane exemplifies the shift from a functionalized molecule to a simple alkane.
• Such reactions are critical in organic synthesis for generating simple hydrocarbons from more complex precursors.

Understanding how alkanes can be formed from other organic compounds provides insights into core processes used in chemical industries, ranging from fuel production to manufacturing various organic chemicals.