Problem 63 - A Complete Resource Book in Chemistry for JEE Main

Question

When ethylene glycol is heated with acidified potassium permanganate, the main organic compound obtained is (a) acetaldehyde (b) glyoxal (c) formic acid (d) oxalic acid

Step-by-Step Solution

Answer

The main organic compound obtained is (d) oxalic acid.

Step 1: Identify the Reactants

The reaction given involves ethylene glycol and acidified potassium permanganate. Ethylene glycol, which is 1,2-ethanediol, is a diol with the chemical structure \( \text{HOCH}_2\text{CH}_2\text{OH} \). Acidified potassium permanganate is a strong oxidizing agent commonly used in organic oxidation reactions.

Step 2: Understanding the Reaction Type

When alcohol groups are oxidized by a strong oxidizer like acidified KMnO ext{4}, they are usually converted to carbonyl compounds such as aldehydes and further oxidation can lead to carboxylic acids or smaller molecules.

Step 3: Predict the Oxidation Outcome

Ethylene glycol contains two primary alcohol (-OH) groups. Upon oxidation by acidified KMnO ext{4}, each -OH group is oxidized first to an aldehyde, and usually, further oxidation occurs to generate carboxylic acids or carbon dioxide. Since ethylene glycol is small and both alcohol groups are primary, oxidation will proceed in several stages.

Step 4: Determine the Main Product

During oxidation of ethylene glycol with KMnO ext{4}, both alcohol groups are oxidized, and given this strong oxidation condition, the final product is typically a dicarboxylic acid. The expected main organic product from this complete oxidation would be oxalic acid \( \text{COOH-COOH} \). Thus (d) oxalic acid is the preferred choice.

Key Concepts

Ethyl Glycol Oxidation

Ethylene glycol is a simple organic compound with the formula \( \text{HOCH}_2 \text{CH}_2 \text{OH} \). It contains two hydroxyl groups, making it a diol. In organic chemistry, the oxidation of alcohols is an important type of reaction that results in the conversion of alcohol groups into carbonyl groups or further. Ethylene glycol oxidation is particularly interesting because it contains two hydroxyl groups, which means there are two possible sites for oxidation to occur.

When ethylene glycol is subjected to oxidation, it initially forms carbonyl compounds. Each hydroxyl group is first oxidized to form an aldehyde; however, due to the presence of a strong oxidizing agent such as potassium permanganate, further oxidation occurs.

In the oxidation of ethylene glycol using a potent oxidizer like acidified potassium permanganate, the process goes through multiple oxidation steps:

• Initially, each hydroxyl group is oxidized to a carbonyl group, forming glyoxal.
• Further oxidation can lead to the formation of carboxylic acids.
• The complete oxidation results in the formation of a dicarboxylic acid, specifically oxalic acid \( \text{COOH-COOH} \).

Understanding this process is crucial in organic synthesis and industrial applications where precise control over oxidation levels is required.

Potassium Permanganate Oxidation

Potassium permanganate (KMnO extsubscript{4}) is a powerful oxidizing agent often used in organic chemistry to oxidize alcohols to carbonyl compounds or even further to carboxylic acids. It is particularly useful because it can proceed at room temperature and be acidic, neutral, or slightly basic, allowing for versatility in reactions.

The role of potassium permanganate in oxidation is significant due to its strong oxidative capabilities, which allow it to add oxygen to other compounds effectively. Its use in ethylene glycol oxidation showcases its efficiency:

• KMnO extsubscript{4} first oxidizes the alcohol groups in ethylene glycol to form aldehydes.
• In the presence of acidic conditions, which enhance oxidative strength, the process continues until stable products like carboxylic acids or even carbon dioxide are formed.
• For ethylene glycol, this results in the production of oxalic acid.

The behavior of KMnO extsubscript{4} is different from milder oxidants, which may halt at the aldehyde stage, illustrating its potency as an oxidizer in organic transformations.

Organic Chemistry Reactions

Organic chemistry reactions encompass a wide range of transformations that alter the structure of organic molecules. Understanding these reactions is key to manipulating organic matter in both lab and industrial settings.

Organic reactions are broadly categorized into several types, such as substitution, elimination, addition, and oxidation-reduction reactions. Oxidation-reduction, or redox reactions, are of particular interest as showcased in the ethylene glycol oxidation.

Reactions involving oxidation use oxidizing agents, such as potassium permanganate, to increase a molecule's oxygen content or decrease the hydrogen content. In the case of ethylene glycol, oxidation follows a stepwise transformation from alcohols to aldehydes and finally to dicarboxylic acids.

When studying organic chemistry reactions like oxidation, consider these topics:

• Reaction mechanisms: Understanding the step-by-step process of how reactants transform into products.
• Reactivity and selectivity: How different conditions and reagents affect reaction pathways.
• Practical applications: How these reactions are used in industrial processes, such as the synthesis of pharmaceuticals or polymers.

This foundational knowledge opens up the ability to predict outcomes in complex chemical reactions, crucial for any aspiring chemist.