Problem 105 - A Complete Resource Book in Chemistry for JEE Main

Question

Isopropyl alcohol is obtained by reacting which of the following alkenes with concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) followed by boiling with water? (a) 2 -methylpropene (b) ethylene (c) isoprene (d) propylene

Step-by-Step Solution

Answer

Propylene (option d) forms isopropyl alcohol when reacted with \( \mathrm{H}_{2} \mathrm{SO}_{4} \) and water.

Step 1: Identify the Reaction Components

The problem states that we need to find the alkene which, when reacted with concentrated \( \mathrm{H}_{2} \mathrm{SO}_{4} \) and then boiled with water, produces isopropyl alcohol. We know that this involves an alkene hydration reaction.

Step 2: Know the Desired Product's Structure

Isopropyl alcohol has the chemical formula \( \mathrm{C}_{3}\mathrm{H}_{8}\mathrm{O} \) and is a secondary alcohol, implying that the hydroxyl group \( \text{-OH} \) is attached to the second carbon of the carbon chain.

Step 3: Analyze Potential Alkenes

Let's consider each option:- (a) 2-methylpropene has a formula of \( \mathrm{C}_4\mathrm{H}_8 \) and forms tert-butyl alcohol when hydrated.- (b) Ethylene \( \mathrm{C}_2\mathrm{H}_4 \) produces ethanol.- (c) Isoprene \( \mathrm{C}_5\mathrm{H}_8 \) is complex with multiple DBs, and doesn't form isopropyl alcohol.- (d) Propylene \( \mathrm{C}_3\mathrm{H}_6 \) can be converted to isopropyl alcohol when hydrated.

Step 4: Determine the Correct Alkene

Since isopropyl alcohol (\( \mathrm{C}_{3}\mathrm{H}_{8}\mathrm{O} \)) results from the hydration of propylene, the correct answer is (d) propylene.

Step 5: Verification of the Reaction

In the reaction of propylene with concentrated \( \mathrm{H}_{2} \mathrm{SO}_{4} \) followed by boiling with water, the double bond of propylene opens up, and water adds across it, forming isopropyl alcohol.

Key Concepts

Isopropyl Alcohol

Isopropyl alcohol, also known as isopropanol or 2-propanol, is a type of alcohol commonly used in industrial and household products. Its chemical formula is \( \mathrm{C}_{3}\mathrm{H}_{8}\mathrm{O} \). This molecule is categorized as a secondary alcohol, which means the hydroxyl group \( \text{-OH} \) is attached to the second carbon atom in the carbon chain.

• It is often used as a disinfectant and cleaning fluid.
• Isopropyl alcohol is volatile and flammable, similar to other alcohols.
• It serves as a common solvent in laboratories and medical settings.

In the context of the hydration reaction, isopropyl alcohol is produced from alkenes like propylene when they react with acids and water. Understanding the synthesis of isopropyl alcohol is crucial for many industrial chemical processes.

Propylene

Propylene, also known as propene, is a colorless gas with the chemical formula \( \mathrm{C}_{3}\mathrm{H}_{6} \). It is a crucial building block in the chemical industry, especially in the production of plastics and alcohols.

• Propylene contains a double bond between two carbon atoms, which makes it an alkene.
• In industrial applications, propylene is typically obtained from the cracking of larger hydrocarbons.
• Its structure enables it to engage in various chemical reactions, such as hydration and oxidation.

The process of alkene hydration uses this double bond. During the hydration of propylene, the double bond opens, and water adds across the bond, producing isopropyl alcohol. The ability to transform this simple molecule into more complex structures is what makes propylene a versatile compound.

Secondary Alcohols

Secondary alcohols are a class of alcohols where the hydroxyl group \( \text{-OH} \) is bound to a carbon atom that is itself connected to two other carbon atoms. This structural arrangement defines many of their chemical properties, which distinguish them from primary and tertiary alcohols.

• Secondary alcohols like isopropyl alcohol have moderate oxidation potential, leading to the formation of ketones.
• They are less reactive than primary alcohols but more so than tertiary alcohols.
• In terms of solubility, secondary alcohols are typically more soluble in water than tertiary alcohols.

An example of a secondary alcohol is isopropyl alcohol, produced via a hydration reaction with propylene. Mastering the structural and chemical properties of secondary alcohols is essential for understanding many biochemical and industrial processes.