Write the mechanism of hydration of ethene to yield ethanol.
The mechanism of hydration of ethene to yield ethanol involves acid-catalyzed hydration. Alkenes react with water in the presence of acid as catalyst to form alcohols. The reaction is: C=C< + H₂O ⇌ C-C< H OH
The mechanism involves three steps:
Step 1: Protonation of alkene to form carbocation by electrophilic attack of H₃O⁺. First, H₂O + H⁺ → H₃O⁺. The alkene then reacts with H₃O⁺: C=C< + H-O⁺-H ⇌ -C-C< + H₂O, forming a carbocation intermediate.
Step 2: Nucleophilic attack of water on carbocation. Water molecule acts as a nucleophile and attacks the carbocation.
In case of unsymmetrical alkenes, the addition reaction takes place in accordance with Markovnikov's rule.
Explanation
The textbook context clearly describes the acid-catalyzed hydration mechanism under section 7.4.1 Preparation of Alcohols. The mechanism involves protonation of the alkene to form a carbocation (Step 1), followed by nucleophilic attack by water (Step 2). The context explicitly states that the mechanism involves three steps and mentions Markovnikov's rule for unsymmetrical alkenes. The reaction is reversible, as indicated by the equilibrium arrows in the context.
Solution Steps
Step 1: Formation of H₃O⁺ from H₂O and H⁺, followed by protonation of alkene to form carbocation
Step 2: Nucleophilic attack of water on the carbocation intermediate
Step 3: Final formation of alcohol product