How is 1-propoxypropane synthesised from propan-1-ol? Write mechanism of this reaction.
1-propoxypropane is synthesised from propan-1-ol by acid-catalyzed dehydration. When propan-1-ol is heated with concentrated sulphuric acid, two molecules of propan-1-ol undergo intermolecular dehydration to form 1-propoxypropane and water.
Mechanism of the reaction:
Step 1: Protonation - The alcohol is protonated by the acid to form an oxonium ion.
Step 2: Nucleophilic attack - Another molecule of propan-1-ol acts as a nucleophile and attacks the protonated alcohol.
Step 3: Deprotonation - The intermediate loses a proton to form the ether (1-propoxypropane) and regenerates the acid catalyst.
The reaction is suitable for primary alcohols like propan-1-ol as they favour substitution over elimination.
Explanation
The textbook context mentions in Question 7.27 that 'Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method,' which implies that acid dehydration IS suitable for primary alcohols like propan-1-ol. The mechanism shown in the context for elimination reactions demonstrates the principles of protonation and carbocation formation, which are adapted for ether formation with primary alcohols. The context also references Williamson's synthesis in Question 7.24 as an alternative method for preparing ethers like 1-propoxypropane, but the specific question asks for synthesis from propan-1-ol directly, which requires acid-catalyzed dehydration.
Solution Steps
Step 1: Identify that propan-1-ol is a primary alcohol suitable for acid-catalyzed dehydration to form ethers
Step 2: Write the reaction: 2 CH₃CH₂CH₂OH → CH₃CH₂CH₂-O-CH₂CH₂CH₃ + H₂O
Step 3: Describe the three-step mechanism: protonation, nucleophilic attack by another alcohol molecule, and deprotonation