Which set of reaction conditions could have been used to obtain the products in the isobutylene Prins reaction with formaldehyde described in the passage?

Questions are based on the following passage: The Prins reaction is the acid-catalyzed addition of aldehydes to alkenes. A general scheme for the Prins reaction is shown in Figure 1. With water and a protic acid as the reaction medium, the 1,3-diol is the reaction product. When water is absent, the allylic alcohol forms. A molar excess of formaldehyde and reaction temperature lower than 70°C gives the dioxane product. The replacement of water with acetic acid forms the corresponding esters. In a putative general mechanism for the Prins reaction using formaldehyde, the first step is the... Show more

Questions are based on the following passage:

The Prins reaction is the acid-catalyzed addition of aldehydes to alkenes. A general scheme for the Prins reaction is shown in Figure 1. With water and a protic acid as the reaction medium, the 1,3-diol is the reaction product. When water is absent, the allylic alcohol forms. A molar excess of formaldehyde and reaction temperature lower than 70°C gives the dioxane product. The replacement of water with acetic acid forms the corresponding esters.


In a putative general mechanism for the Prins reaction using formaldehyde, the first step is the protonation of the oxygen in formaldehyde to form a carbocation, followed by the addition of the alkene (CH2 = CRR') to form a new carbocation X (Figure 2A). Carbocation X then reacts with water to form the 1,3-diol. The 1,3-diol is then protonated at its alcohol, forming water as a leaving group, which makes the allylic alcohol product. Carbocation X also reacts with the aldehyde to form a linear ether−containing carbocation, which cyclizes to form the 1,3-dioxane product.

The Prins reaction was performed by reacting isobutylene (Figure 2B) with formaldehyde. The main products formed are 75% 1,3-dioxane (Figure 2C) and 9% 1,3-diol.

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