Q28E - Organic Chemistry (Mcmurry)

Question

Treatment of the following epoxide with aqueous acid produces a carbocation intermediate that reacts with water to give a diol product. Show the structure of the carbocation, and propose a mechanism for the second step.

Step-by-Step Solution

Answer

The mechanism that followed shown below as:

Step1: Reaction of epoxide

Epoxide on reaction with acid catalyst opens as an electrophile on the addition of the proton of acid, and the formation of alcohol occurs.

The hydroxyl group and the alkyl group have a trans relation with each other.

Step 2: Formation of intermediate

In the reaction of alcohol with sulfuric acid, the catalyst formation of alkyloxonium, an ion, occurs, followed by the addition of water molecules. Next by the addition of the base, a hydrogen ion is lost,  and the formation of the hydroxyl group occurs.

Step 3: Mechanism

1. protonation

2. loss of water

3. loss of hydrogen proton

4. formation of hydroxyl