Problem 68 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{A} \frac{\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}}{\mathrm{H}_{2} \mathrm{SO}_{4}}-\mathrm{B} \underset{\text { vigrous oxidation }}{[\mathrm{O}]} \mathrm{CH}_{3} \mathrm{COOH}\) Here, B is propanone so A will be (a) Ethyl alcohol (b) Isopropyl alcohol (c) n-propyl alcohol (d) tertiary butyl alcohol

Step-by-Step Solution

Answer

The correct answer is (b) Isopropyl alcohol.

Step 1: Identify the Reaction Process

The problem involves a vigorous oxidation reaction where compound B, propanone (acetone), is formed from an alcohol (compound A) using an oxidizing agent, potassium dichromate (K₂Cr₂O₇), in a sulfuric acid medium (H₂SO₄). The reaction aims to identify the precursor alcohol that gets oxidized to propanone.

Step 2: Recall the Oxidation Pathway of Alcohols

In organic chemistry, secondary alcohols are oxidized to produce ketones. Propanone, being a ketone, suggests it is derived from the oxidation of a secondary alcohol.

Step 3: Identify Secondary Alcohol

Among the options, identify which alcohol is a secondary alcohol. Secondary alcohols have the -OH group attached to a carbon atom that is connected to two other carbon atoms. Check the options: (a) Ethyl alcohol - primary (b) Isopropyl alcohol - secondary (c) n-propyl alcohol - primary (d) tertiary butyl alcohol - tertiary

Step 4: Determine the Correct Answer

Since isopropyl alcohol is a secondary alcohol and can be oxidized to produce propanone, the correct answer is: (b) Isopropyl alcohol.

Key Concepts

Propanone Formation

Propanone, commonly known as acetone, is a simple ketone with the chemical formula \( ext{CH}_3 ext{COCH}_3 \). It is an important compound in organic chemistry due to its wide range of applications and as a precursor in various chemical reactions. The formation of propanone typically involves the oxidation of a secondary alcohol. In the context of the given problem, propanone is formed from isopropyl alcohol during a vigorous oxidation process. Here, the oxidizing agent used is potassium dichromate \( ext{K}_2 ext{Cr}_2 ext{O}_7 \), in an acidic medium like sulfuric acid \( ext{H}_2 ext{SO}_4 \).During oxidation, the secondary alcohol loses hydrogen atoms and gains oxygen atoms, converting into a ketone. This process is crucial in differentiating between alcohols based on their reactivity and structure. Understanding the formation of propanone is especially important for students learning about the behavior of alcohols in oxidation reactions.

Secondary Alcohol Oxidation

Secondary alcohols, such as isopropyl alcohol, are characterized by having their hydroxyl group (\(- ext{OH}\)) attached to a carbon atom that is also bonded to two other carbon atoms. This distinguishes them from primary and tertiary alcohols, impacting their oxidation pathways and products.When a secondary alcohol undergoes oxidation, it typically forms a ketone. This process is facilitated by strong oxidizing agents, such as potassium dichromate, and often occurs in an acidic medium like sulfuric acid. The reaction generally follows this pathway:

• Loss of two hydrogen atoms from the alcohol.
• Formation of a double bond between the oxygen and the carbon, resulting in a ketone.

In the exercise context, isopropyl alcohol is oxidized to propanone. It's important to grasp the structural changes that occur during such reactions to understand the differences in reactivity among alcohol types. Oxidation reactions serve as a foundation in organic synthesis and are key to producing various chemical compounds.

Organic Chemistry Reactions

Organic chemistry is the study of carbon-containing compounds and their reactions. It covers a wide range of transformations, including oxidation reactions like the one described in the exercise. These reactions involve the conversion of alcohols into carbonyl compounds, such as aldehydes, ketones, and carboxylic acids. In organic chemistry:

• Oxidation reactions are crucial for understanding how different functional groups transform.
• Secondary alcohol oxidation results in ketones, which are important for industrial and laboratory synthesis.
• Different oxidizing agents can selectively convert alcohols, highlighting their application in synthetic chemistry.

Recognizing how these transformations occur and the factors influencing them, such as the type of oxidizing agent and the specific substrate, helps students predict reaction outcomes and design synthetic pathways. Mastery of these reactions allows for the advancement of organic chemistry, leading to the development of new materials and medicinal compounds.