Question

\(\mathrm{CH}_{3} \mathrm{CHO}\) can be oxidised in ester effectively by : (A) \(\mathrm{Al}\left(-\mathrm{OCH}_{2} \mathrm{CH}_{3}\right)_{3}\) (B) \(\mathrm{AgNO}_{3} / \mathrm{NH}_{4} \mathrm{OH}\) (C) \(\mathrm{Cu}_{2} \mathrm{Cl}_{2} / \mathrm{NH}_{4} \mathrm{OH}\) (D) \(\mathrm{m}-\mathrm{CPB} \mathrm{A}\)

Short answer

The effective oxidising agent to convert acetaldehyde (\(\mathrm{CH}_{3} \mathrm{CHO}\)) into an ester is (B) \(\mathrm{AgNO}_{3} / \mathrm{NH}_{4} \mathrm{OH}\).

Step-by-step solution

Identify the given compound

The given compound is \(\mathrm{CH}_{3} \mathrm{CHO}\), which is acetaldehyde. Our task is to find the appropriate oxidising agent to oxidize it into an ester.

Analyse each oxidising agent

Let's look at each option one by one and determine if it can effectively oxidize acetaldehyde into an ester: (A) \(\mathrm{Al}\left(-\mathrm{OCH}_{2} \mathrm{CH}_{3}\right)_{3}\): This is an aluminum-based compound, which is a Lewis acid, not an oxidizing agent. It cannot oxidize acetaldehyde to an ester. (B) \(\mathrm{AgNO}_{3} / \mathrm{NH}_{4} \mathrm{OH}\): This mixture contains silver nitrate and ammonium hydroxide. Silver ions are mildly oxidizing agents, which can effectively convert aldehydes into carboxylic acids or esters under controlled conditions, such as using Tollen's reagent (\(\mathrm{Ag}(\mathrm{NH}_{3})_{2}^+\)). This is a promising candidate. (C) \(\mathrm{Cu}_{2} \mathrm{Cl}_{2} / \mathrm{NH}_{4} \mathrm{OH}\): This mixture contains copper(II) chloride and ammonium hydroxide. Copper(II) ions are only weak oxidizing agents and can convert aldehydes into carboxylic acids but not very effectively into esters. (D) \(\mathrm{m}-\mathrm{CPB} \mathrm{A}\): This is meta-Chloroperoxybenzoic acid (mCPBA), which is an organic peroxide and a strong oxidizing agent. It can oxidize various functional groups, such as alkenes to epoxides and sulfides to sulfoxides. However, it isn't known for directly oxidizing aldehydes to esters.

Choose the correct oxidising agent

Based on our analysis, the effective oxidising agent to convert \(\mathrm{CH}_{3} \mathrm{CHO}\) (acetaldehyde) into an ester is: (B) \(\mathrm{AgNO}_{3} / \mathrm{NH}_{4} \mathrm{OH}\)

Key concepts

Oxidizing Agents

Oxidizing agents are substances that have the ability to oxidize other compounds. They accept electrons from a substance, consequently reducing themselves. This action allows the oxidizing agent to convert molecules into more oxidized forms, like converting aldehydes into carboxylic acids or further into esters.

These agents have varying strengths and specificities. For instance:

• Strong oxidizing agents, such as permanganates, can oxidize a wide range of functional groups.
• Selective oxidizing agents, like Tollens' reagent, selectively oxidize specific groups.

Understanding the appropriate oxidizing agent for a reaction is crucial because it affects the products formed. Using the correct oxidizing agent means achieving the desired transformation efficiently without undesired side reactions.

Acetaldehyde

Acetaldehyde, with the chemical formula \(\mathrm{CH_3CHO}\), is one of the simplest aldehydes. Its structure consists of a carbonyl group attached to a methyl group. It's a highly reactive compound and is common in many industrial and biological processes.

When oxidized, acetaldehyde can be converted into different products, depending on the oxidizing agent used:

• Weak oxidizing agents may oxidize it to acetic acid.
• Under specific conditions, it can be further converted into esters.

This versatility makes acetaldehyde an important compound in organic synthesis. By choosing the correct method, acetaldehyde can undergo reactions that lead to a variety of meaningful chemical transformations.

Esterification

Esterification is the chemical process of forming an ester. It typically involves the reaction between an alcohol and a carboxylic acid in the presence of an acid catalyst.

During this process, a water molecule is typically produced as the alcohol and acid combine:

• This transformation is crucial in producing esters, which are widely used in flavorings, fragrances, and polymers.
• Oxidizing agents can sometimes play a role in this transformation by first preparing the necessary intermediates, like turning aldehydes into carboxylic acids before reaction with alcohols.

The importance of esterification cannot be understated, as it is not only fundamental in organic chemistry but also in industrial applications involving the synthesis of various functional products.

Tollens' Reagent

Tollens' reagent is a versatile oxidizing agent primarily used to detect the presence of aldehydes, including acetaldehyde. It's an ammoniacal solution of silver nitrate consisting of \(\mathrm{Ag(NH_3)_2^+}\) complex ions, which make it a mild yet selective oxidizer.

When reacted with aldehydes, Tollens' reagent oxidizes them to carboxylic acids or further products under specific conditions:

• This results in the reduction of silver ions to metallic silver, which is deposited as a mirror-like coating on the reaction vessel, known as the "silver mirror test."
• It's not typically used for esterification directly but can prepare aldehydes for subsequent reactions, contributing to the formation of esters.

Tollens' reagent is especially useful in qualitative analysis in laboratories, giving clear indications of aldehyde presence and helping guide further chemical experiments.