Both 1,2 -diols and 1,3 -diols can be protected by treatment with 2-methoxypropene according to the following reaction. (a) Propose a mechanism for the formation of this protected diol. (b) Suggest an experimental procedure by which this protecting group can be removed to regenerate the unprotected diol.

1. Formation of carbocation In the first step, 2-methoxypropene undergoes the ionization process to generate a tertiary carbocation and hydroxide ion. This process occurs due to the presence of a strong acid catalyst in the reaction mixture. 2-methoxypropene ->[\(H^+\)][-OH] Tertiary carbocation + OH^- 2. Nucleophilic attack After the tertiary carbocation is formed, it can act as a great electrophile. The diol (1,2-diol or 1,3-diol) has two hydroxyl groups which can act as nucleophiles. The nucleophilic hydroxyl will attack the carbocation, forming a bond with the electrophilic carbon center. This bond formation will result in a protected diol molecule with an acetal group. Tertiary carbocation + Hydroxyl group of diol -> Acetal-protected diol

To remove the protecting group and regenerate the unprotected diol, we need to carry out an experimental procedure that reverses the steps mentioned in part (a). This can be done using hydrolysis under acidic conditions. 1. Add an aqueous acid The first step is to add an aqueous acid, like hydrochloric acid (HCl), to the reaction mixture containing the protected diol. The acidic conditions will help promote hydrolysis and cleaving of the acetal protecting group. 2. Heat the mixture Heat the reaction mixture to facilitate hydrolysis and promote the acid-catalyzed cleavage of the protecting group. This will generate the carbocation and the regenerated diol with two free hydroxyl groups. 3. Isolate the diol The last step is to isolate the unprotected diol from the reaction mixture. This can be achieved by using different techniques like extraction or distillation, depending on the specific properties of the diol. The overall process can be summarized as: Acetal-protected diol->[HCl][Heat] Unprotected diol + 2-methoxypropene