Problem 113 - A Complete Resource Book in Chemistry for JEE Main

Question

The reagent used for the preparation of higher ethers from halogenated ethers is (a) sodium alkoxide (b) Grignard reagent (c) concutrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (d) dry silver oxide

Step-by-Step Solution

Answer

The reagent used is sodium alkoxide (option a).

Step 1: Understanding Ethers

Ethers are a class of organic compounds that have an oxygen atom connected to two alkyl or aryl groups. In this exercise, we are focused on preparing higher ethers, which means forming ethers with longer or more complex carbon chains.

Step 2: Identifying the Role of Reagents

The reagent needed must facilitate the conversion of halogenated ethers to higher ethers. For this, a reagent that can effectively replace the halogen atom with an alkoxide ion is ideal, as the alkoxide can act as a nucleophile, attacking the carbon the halogen is attached to.

Step 3: Analyzing Sodium Alkoxide

Sodium alkoxide is commonly used in the Williamson Ether Synthesis, where it reacts with halogenated compounds to form ethers through a nucleophilic substitution reaction. It is suitable for the preparation of both simple and higher ethers.

Step 4: Evaluating the Options

Let's assess the options: - (a) Sodium alkoxide is known for its use in ether synthesis.- (b) Grignard reagent typically forms alcohols and is not suitable for ether preparation.- (c) Concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is used for dehydration reactions, not ether synthesis.- (d) Dry silver oxide is not commonly used for ether synthesis.

Step 5: Selecting the Correct Answer

Based on the analysis, sodium alkoxide is the reagent that directly facilitates the preparation of ethers from halogenated ethers through the Williamson synthesis approach. It fits the requirement for forming higher ethers.

Key Concepts

Ether Synthesis

In organic chemistry, ether synthesis is a fundamental method for creating organic compounds where an oxygen atom links two carbon-containing groups. The Williamson Ether Synthesis is a classic approach used to produce ethers efficiently. This process involves the reaction of an alkoxide ion with a primary alkyl halide or tosylate, forming a new ether linkage.

Key traits of this synthesis include:

• Simultaneous **nucleophilic attack** and **leaving group departure**, resulting in direct production of an ether.
• Applicable to create both **simple** and **more complex ethers** with varying chain lengths.

As we prepare for the synthesis of higher ethers, the structure of starting materials needs careful consideration. Ensuring minimal steric hindrance in the alkyl halide can lead to a better yield and smoother reactions.

Sodium Alkoxide

Sodium alkoxides are pivotal in the Williamson Ether Synthesis due to their role as a reactive nucleophile. When a sodium atom binds with an alkoxide ion, it forms a strong base capable of displacing a halide ion in a substitution reaction.

Sodium alkoxides are tailored for effectiveness based on the type of ether being prepared:

• Common types include **sodium methoxide** (\( ext{CH}_3 ext{ONa} \)) and **sodium ethoxide** (\( ext{C}_2 ext{H}_5 ext{ONa}\)), selected based on the desired ether.
• These compounds are typically synthesized in situ from alcohols treated with sodium metal.

In the synthesis process, the basicity of sodium alkoxide is crucial. It makes sodium alkoxide reactive enough to engage in a swift Williamson Ether reaction, producing ethers efficiently.

Nucleophilic Substitution Reaction

Nucleophilic substitution reactions are integral to the formation of ethers in organic chemistry, especially in the context of the Williamson Ether Synthesis. In this reaction type, a nucleophile is attracted to an electrophilic center, such as a carbon atom attached to a leaving group like a halide.

The **nucleophile** (in this case, the alkoxide ion) initiates the reaction:

• The process involves **bimolecular substitution (S_N2 reaction)**, where the nucleophile attacks the substrate carbon, forcing the simultaneous ejection of the leaving group.
• This results in the formation of a new bond between the oxygen of the alkoxide and the substrate carbon, leading to the creation of the ether.

Understanding the intricacies of nucleophilic substitution is crucial for success in ether synthesis, ensuring efficient conversion of reactants to the desired ether products.