Problem 38 - A Complete Resource Book in Chemistry for JEE Main

Question

In Williamson synthesis, ethoxyethane is prepared by (a) heating sodium ethoxide with ethyl bromide (b) passing ethanol over heated alumina (c) heating ethanol with dry \(\mathrm{Ag}_{2} \mathrm{O}\) (d) treating ethyl alcohol with excess of at \(430-440 \mathrm{~K}\)

Step-by-Step Solution

Answer

(a) heating sodium ethoxide with ethyl bromide.

Step 1: Understand Williamson Synthesis

Williamson synthesis is a method used to prepare ethers by reacting a sodium alkoxide with an alkyl halide. Ethoxyethane, which is a type of ether, can be synthesized using this method.

Step 2: Identify the Reactants in Williamson Synthesis

For Williamson synthesis to occur, sodium ethoxide (an alkoxide) is needed to react with an alkyl halide. In this context, sodium ethoxide reacts with ethyl bromide to form ethoxyethane.

Step 3: Evaluate Each Option

Option (a) describes heating sodium ethoxide with ethyl bromide, which matches the Williamson synthesis process of forming ethoxyethane. Options (b), (c), and (d) involve different chemical processes and do not use sodium ethoxide with an alkyl halide.

Step 4: Select the Correct Option

Based on the requirements of Williamson synthesis, heating sodium ethoxide with ethyl bromide correctly creates ethoxyethane. Therefore, option (a) is the correct choice.

Key Concepts

Sodium Ethoxide

Sodium ethoxide is a vital component in the world of organic synthesis. It is a type of alkoxide, which means it's an ion made from an alcohol where a hydrogen atom is replaced by a sodium atom. This transformation is crucial because sodium ethoxide acts as a strong base and a good nucleophile.

• Strong Base: In solutions, sodium ethoxide can deprotonate weakly acidic hydrogen atoms, a common step in many organic reactions. This makes it essential for eliminations and substitutions.
• Good Nucleophile: It is highly reactive towards electrophiles, like alkyl halides, which makes it perfect for the Williamson synthesis.

In the practical lab world, sodium ethoxide is typically prepared by dissolving sodium metal in ethanol, resulting in a strong, highly reactive solution ready for use in various organic reactions. It's especially useful in the creation of ethers through the Williamson synthesis. This reaction showcases sodium ethoxide's ability to efficiently bond with other molecules, expanding the diversity of chemical structures we can create.

Alkyl Halide

Alkyl halides are a group of chemical compounds in which a halogen atom (like chlorine, bromine or iodine) is bonded to an alkyl group. These compounds play a significant role in organic chemistry because of their high reactivity.

• Electrophilic Centers: The carbon atom directly bonded to the halogen becomes electrophilic, making it susceptible to attacks by nucleophiles.
• Halogen Reactivity: The bond between carbon and halogen is polarized, with the carbon being slightly positive, thus easy for nucleophiles like sodium ethoxide to attack it.

In the context of Williamson synthesis, an alkyl halide such as ethyl bromide reacts with a nucleophile like sodium ethoxide to form an ether. This reaction path clearly shows how the polar carbon-halogen bond in alkyl halides is effectively utilized, leading to the synthesis of new organic compounds. Ethyl bromide, specifically, is often used due to its ideal reactivity in these processes.

Ethoxyethane

Ethoxyethane, also known as diethyl ether, is a common ether with the chemical formula \( C_4H_{10}O \). It has interesting properties that make it crucial in both laboratory and industrial settings.

• Solvent Use: Due to its low boiling point and good miscibility with various organic compounds, ethoxyethane is a widely used solvent, especially in extractions and during synthesis reactions.
• Easily Volatilizable: It is highly volatile, making it easy to remove from reaction mixtures by simple distillation.

In Williamson synthesis, ethoxyethane is synthesized by the reaction between sodium ethoxide and ethyl bromide, showcasing a classic example of ether formation. The ether linkage in ethoxyethane (\(-O-\)) is a result of the nucleophilic attack by sodium ethoxide on the ethyl group of ethyl bromide, demonstrating the efficient use of both starting materials in forming this valuable organic compound.