15.18 : Dehydration of Aldols to Enones: Acid-Catalyzed Aldol Condensation

As shown in Figure 1, under acidic conditions, the β-hydroxy ketone undergoes dehydration via an E1 elimination reaction to form an enone.

Figure 1. The dehydration reaction of a β-hydroxy ketone.

Figure 2 depicts the sequential processes involved in the mechanism of the reaction. Here, the acid protonates the hydroxyl group in the β-hydroxy ketone to form a hydrated hydroxyl group, which then departs to form a tertiary carbocation intermediate. Subsequently, the loss of the hydrogen atom from the α carbon yields an enone as the final product.

Figure 2. The mechanism of the dehydration reaction of a β-hydroxy ketone.