Problem 25 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

When ethane-1,2-dioic acid is heated with conc. \(\mathrm{H}_{2} \mathrm{SO}_{4^{\prime}}\) it gives (a) \(\mathrm{CO}+\mathrm{HCOOH}\) (b) \(\mathrm{CO}_{2}+\mathrm{HCOOH}\) (c) \(\mathrm{CO}+\mathrm{CO}_{2}+\mathrm{HCOOH}\) (d) \(\mathrm{CO}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The answer is (d) \(\mathrm{CO} + \mathrm{CO}_{2} + \mathrm{H}_{2} \mathrm{O}\).

Step 1: Identify the Compound

Ethane-1,2-dioic acid is known as oxalic acid with a chemical formula of \( ext{C}_2 ext{H}_2 ext{O}_4\).

Step 2: Understand Reaction with Conc. Sulfuric Acid

When oxalic acid is heated with concentrated \( ext{H}_2 ext{SO}_4\), it undergoes dehydration. Concentrated sulfuric acid acts as a dehydrating agent, causing oxalic acid to decompose.

Step 3: Determine the Products of Decomposition

Oxalic acid, \( ext{C}_2 ext{H}_2 ext{O}_4\), breaks down to form carbon monoxide (CO), carbon dioxide (CO\(_2\)), and water (H\(_2\)O) when treated with concentrated sulfuric acid.

Step 4: Select the Correct Answer

Based on the decomposition reaction, the products formed are \( ext{CO} + ext{CO}_2 + ext{H}_2 ext{O}\). Therefore, the correct answer is option (d).

Key Concepts

Oxalic acid decomposition

Oxalic acid, chemically known as ethane-1,2-dioic acid, is represented as \( \text{C}_2 \text{H}_2 \text{O}_4 \). This compound is interesting because it readily undergoes decomposition upon heating, especially in the presence of certain substances. Decomposition is a process where a compound breaks down into simpler chemical species. For oxalic acid, this occurs via thermal decomposition and is often facilitated by a catalyst or an agent like sulfuric acid.
When oxalic acid decomposes, it primarily splits into carbon monoxide (\( \text{CO} \)), carbon dioxide (\( \text{CO}_2 \)), and water (\( \text{H}_2\text{O} \)).
One thing to remember is:

• Oxalic acid is a reducing agent.
• Its decomposition involves the conversion of some elements to a more oxidized form (\( \text{CO}_2 \)) and some to a reduced form (\( \text{CO} \)).
• It is an endothermic reaction, meaning it absorbs heat.

This is crucial in many industrial processes where gases like carbon monoxide and carbon dioxide are desired.

Sulfuric acid as dehydrating agent

Concentrated sulfuric acid (\( \text{H}_2 \text{SO}_4 \)) is renowned for its role as a strong dehydrating agent. A dehydrating agent is a substance that removes water from other compounds, effectively driving certain chemical reactions forward by reducing the water content.
When applied to oxalic acid, sulfuric acid induces the removal of water from the molecular structure, facilitating its decomposition:

• This process involves breaking the covalent bonds within oxalic acid.
• The output is a release of water along with the formation of carbon monoxide and carbon dioxide.
• The dehydration is a necessary step before the actual breakdown of the molecule into these gases.

Sulfuric acid's strong affinity for water molecules makes it ideal for reactions where water need to be driven off to favor product formation. Its capability goes beyond just dehydration; it can also catalyze reactions by making certain pathways more viable.

Thermal decomposition reactions

Thermal decomposition is a chemical reaction where a compound breaks down into two or more substances when it is heated. A classic example is the breakdown of oxalic acid into gases, as mentioned before.
This process is crucial because:

• It requires heat to overcome the activation energy necessary for the reaction to occur.
• Decomposition reactions are generally endothermic, meaning they absorb energy (heat) from their surroundings.
• They are essential in industries for extracting elements or removing unwanted substances from compounds.

For example, in oxalic acid decomposition:

• Heating provides the energy needed for the breaking of chemical bonds in the compound.
• The products include more stable molecules like carbon monoxide and carbon dioxide.

Thus, understanding thermal decomposition helps in recognizing how heat can be utilized for chemical transformations in laboratory and industrial settings.