Explain how 2-hexanol is prepared by acid catalyzed hydration of an appropriate alkene showing the reaction mechanism as well

Answer 1

2-Hexanol can be synthesized through the acid-catalyzed hydration of 1-hexene, which is an appropriate alkene for this reaction. The process involves adding water across the double bond of the alkene in the presence of an acid catalyst, typically sulfuric acid or another strong acid. Below is an explanation of the preparation, along with the mechanistic steps involved.

Preparation of 2-Hexanol

1. Starting Alkene: The starting material is 1-hexene (CH₃(CH₂)₄CH=CH₂).

2. Acid-Catalyzed Hydration Reaction: The overall reaction can be represented as follows: \[ \text{CH₃(CH₂)₄CH=CH₂} + \text{H₂O} \xrightarrow{\text{H}^+} \text{CH₃(CH₂)₄CHOHCH₃} \] This reaction yields 2-hexanol (CH₃(CH₂)₄CHOHCH₃).

Mechanistic Steps:

1. Protonation of the Alkene: The first step involves the protonation of the alkene, where the double bond of 1-hexene attacks a proton (H⁺) from the acid catalyst.

   \[ \text{CH₃(CH₂)₄CH=CH₂} + \text{H}^+ \rightarrow \text{CH₃(CH₂)₄C}^+(H)CH₂ \]

   This forms a more stable, tertiary carbocation at the 2-position.

2. Nucleophilic Attack by Water: Next, water (acting as a nucleophile) attacks the carbocation. The oxygen of water has a pair of electrons that can be donated to the positively charged carbon atom.

   \[ \text{CH₃(CH₂)₄C}^+(H)CH₂ + \text{H₂O} \rightarrow \text{CH₃(CH₂)₄C(OH)(H)CH₂}^+ \]

   This step forms an oxonium ion (protonated alcohol).

3. Deprotonation: In the final step, the oxonium ion loses a proton to give the neutral alcohol 2-hexanol.

   \[ \text{CH₃(CH₂)₄C(OH)(H)CH₂}^+ \rightarrow \text{CH₃(CH₂)₄CHOHCH₃} + \text{H}^+ \]

Overall Reaction Summary:

Putting it all together, the overall transformation is the hydration of 1-hexene to yield 2-hexanol via an acid-catalyzed mechanism that includes protonation, nucleophilic attack, and deprotonation.

Key Points:

• The reaction proceeds via a carbocation intermediate, which shows Markovnikov's rule at work, where the nucleophile (water) adds to the more substituted carbon atom of the alkene.
• This method is advantageous for producing alcohols with good yields and can be carried out under relatively mild conditions compared to other methods.
• The reaction is often carried out in an aqueous solution with strong acid to enhance the rate and efficiency of the hydration process.