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

Oxalic acid is the main compound formed.

Step 1: Understanding the Reactants

Identify the reactants in the chemical reaction. We have ethylene glycol and acidified potassium permanganate. Ethylene glycol is an alcohol with the formula \(C_2H_6O_2\), and potassium permanganate \((KMnO_4)\) is a strong oxidizing agent used in acidic conditions.

Step 2: Predicting the Reaction

Ethylene glycol will undergo oxidation when treated with an acidified oxidizing agent like potassium permanganate. Potassium permanganate in acid generally oxidizes alcohols to carboxylic acids or other oxygenated compounds.

Step 3: Determine the Oxidation Products

Recognize that ethylene glycol, as a diol, can be oxidized to different products. In this scenario, we focus on the main compound formed, which involves breaking the carbon-carbon bond and fully oxidizing both to their respective carboxyl groups.

Step 4: Identifying the Main Product

The main organic compound obtained when ethylene glycol is oxidized by acidified \(KMnO_4\) is oxalic acid \((C_2H_2O_4)\). This is because both the hydroxyl groups of ethylene glycol are oxidized, leading to the formation of oxalic acid.

Key Concepts

Ethylene Glycol

Ethylene glycol is a simple yet fascinating molecule, often known for its use in antifreeze and de-icing solutions. Its chemical formula is \(C_2H_6O_2\), and it's characterized by having two hydroxyl (\(-OH\)) groups. These alcohol groups make ethylene glycol a type of alcohol called a diol, specifically a vicinal diol since the \(-OH\) groups are on adjacent carbon atoms.
When ethylene glycol enters an oxidation reaction, these hydroxyl groups are crucial because they tend to be sites where the reaction will occur. During oxidation, the oxygen from an oxidizer, like potassium permanganate, interacts with the hydrogen atoms of the \(-OH\) groups. This reaction is characteristic because it leads to the conversion of alcohols into more oxidized compounds such as aldehydes, ketones, or acids, depending on the conditions and reagents used.
In this context, ethylene glycol serves as a classic example of how simple organic compounds can be transformed into entirely new substances through oxidative processes.

Acidified Potassium Permanganate

Potassium permanganate \((KMnO_4)\) is a strong oxidizing agent that is often used to oxidize alcohols and other organic compounds. When it is 'acidified,' typically by adding sulfuric acid \((H_2SO_4)\), it becomes especially efficient in facilitating oxidation reactions.
Acidified potassium permanganate is a powerful tool in chemistry labs. It is known for its ability to completely oxidize alcohols to carboxylic acids and other oxygenated products. Its oxidizing power comes from the manganese atom, which is in its highest oxidation state of +7. During reactions, the manganese is reduced, often turning from purple to faint pink or brown, indicating the progress of the reaction.
In the specific reaction with ethylene glycol, acidified potassium permanganate helps break down the carbon-carbon bond and oxidize the alcohol groups to carboxyl groups. This explains how ethylene glycol is transformed into oxalic acid in this oxidation process.

Oxalic Acid

Oxalic acid \((C_2H_2O_4)\), also known as ethanedioic acid, is one of the simplest dicarboxylic acids. It is the main product formed when ethylene glycol is oxidized by acidified potassium permanganate.
In terms of structure, oxalic acid consists of two carboxyl groups \(\text{(-COOH)}\) each bonded to a carbon atom. These atoms are linked by a carbon-carbon bond, forming a simple linear molecule. This complete transformation under oxidation converts the hydroxy groups in ethylene glycol into carboxyl groups of oxalic acid.
Oxalic acid is commonly found in plants, but it can also be produced synthetically. It is used in various applications, from cleaning agents to rust removers. Its transformation from ethylene glycol in an oxidizing reaction highlights the versatility and reactivity of organic molecules under the right conditions. The ability of simple molecules like ethylene glycol to morph into different substances showcases the principle that underpins so much of organic chemistry.