Problem 25 - A Complete Resource Book in Chemistry for JEE Main

Question

Glycerol on heating with oxalic acid at \(110^{\circ} \mathrm{C}\) gives (a) ethanol (b) formic acid (c) ethanal (d) ether

Step-by-Step Solution

Answer

Formic acid is produced when glycerol is heated with oxalic acid at \(110^{\circ}C\).

Step 1: Identify Reactants and Conditions

The problem involves heating glycerol (propane-1,2,3-triol) with oxalic acid at a temperature of \(110^{\circ}C\). Recognizing the reactants and the conditions is crucial for predicting the chemical reactions that might occur.

Step 2: Analyze Possible Reactions

When glycerol is heated with oxalic acid, a decomposition reaction occurs. At around \(110^{\circ}C\), oxalic acid decomposes to formic acid and carbon dioxide. Glycerol can then react with the formic acid produced during this process.

Step 3: Identify the Product Formation

The formic acid that forms reacts further with the glycerol. This reaction results in the formation of formic esters and the liberation of water. Since we are looking for products, formic acid is a primary candidate.

Step 4: Evaluate the Options

The problem asks which of the given options is produced under the reaction conditions: - (a) ethanol: not typically produced with glycerol and oxalic acid - (b) formic acid: directly forms from the decomposition of oxalic acid - (c) ethanal: unlikely to form under these conditions - (d) ether: not relevant to the reaction Hence, formic acid is the most likely product.

Key Concepts

Glycerol Chemistry

Glycerol, also known as propane-1,2,3-triol, is a colorless, odorless, viscous liquid that has three hydroxyl (OH) groups. These groups make glycerol a type of alcohol, more specifically a polyol due to its multiple alcohol groups. Glycerol is soluble in water, which allows it to participate in various chemical reactions and makes it a versatile substance in both industrial and scientific contexts.

Glycerol is commonly used in the production of soaps and cosmetics due to its hygroscopic nature, meaning it attracts moisture from the air. Its chemical properties, including the ability to form esters and ethers, make it a key ingredient in the manufacturing of many products.

• Reactivity with Acids: Glycerol can react with acids in esterification reactions where hydroxyl groups form esters and release water.
• Industrial Uses: Aside from cosmetics, glycerol's non-toxic attribute makes it suitable for food and pharmaceutical applications.
• Chemical Structure: The molecular formula of glycerol is \( C_3H_8O_3 \), and its structure can be described as a carbon chain with three attached OH groups.

Understanding glycerol's chemistry provides insight into its behavior and reactions in various chemical processes, such as when mixed with oxalic acid, where its properties change subtly under heat to produce different compounds.

Oxalic Acid Reactions

Oxalic acid is an organic compound with the formula \( C_2H_2O_4 \) and is known as a simple carboxylic acid. It naturally occurs in many plants and vegetables, often involved in plant metabolism. When in pure form, it appears as a white crystalline solid that is highly soluble in water.

Oxalic acid is characterized by its ability to donate protons, interacting with bases to form salts and other compounds. Upon heating, particularly when the temperature reaches around \(110^{\circ}C\), oxalic acid undergoes decomposition, which is crucial in understanding its reactivity profile with other substances.

• Decomposition: When heated, oxalic acid decomposes into formic acid and carbon dioxide. Formic acid is another simple acid that can further participate in chemical reactions.
• Uses in Chemistry: Oxalic acid is used for rust removal, due to its ability to react with iron oxides, and as a mordant in dyeing processes.
• Medical and Toxicity Considerations: Despite its presence in some foods, oxalic acid should be consumed in moderation as high intakes can lead to kidney stones.

In chemical reactions such as with glycerol, oxalic acid's decomposition plays a pivotal role in the creation of new compounds, emphasizing its importance in organic synthesis.

Decomposition Reactions

Decomposition reactions are a type of chemical reaction where one compound breaks down into two or more simpler substances. These reactions are critical in chemistry and are characterized by their ability to release energy, often as heat, light, or electricity. They usually require some form of energy input, such as heat or light, to occur.

In the context of glycerol and oxalic acid, a decomposition reaction is pivotal. Oxalic acid, when heated, breaks down into formic acid and carbon dioxide, demonstrating a classic case of decomposition reaction:

• Role in Synthesis: Decomposition reactions are essential in the synthesis of materials, especially when new compounds need to be created from existing materials.
• Energy Aspect: These reactions are endothermic, meaning that they absorb energy, often requiring a heat source to sustain.
• Common Examples: Besides oxalic acid, other examples include the decomposition of calcium carbonate to calcium oxide and carbon dioxide, as well as the electrolysis of water to hydrogen and oxygen.

This understanding of decomposition reactions is crucial, especially when predicting the products of a reaction involving complex substances such as glycerol and oxalic acid. It aids in elucidating the possible pathways and outcomes when such compounds are subjected to specific conditions.