MCAT Chemical and Physical Foundations of Biological Systems 8 — Flashcards

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.