Mechanism of dehydration:

If the above reaction is performed with heating, after that a different product is acquired. This occurs from elimination of a molecule of water from the Aldol reaction product. There are two causes why this can take place.

Figure: Formation of 2-butenal.

Very first, the product still has an acidic proton (that is there are still a carbonyl group exist and an α-hydrogen next to it). This type of proton is prone to attack from base. Secondly, the dehydration process results in a conjugated product that results in raised stability. The mechanism of dehydration is displayed in below figure. Very firstly, the acidic proton is removed and a new enolate ion is created. After that the electrons in the enolate ion can move in such a fashion that the hydroxyl group is expelled to provide the last product - an α, β-unsaturated aldehyde.

Figure: Mechanism of dehydration.

In this instance, it is probable to vary the conditions like that one acquires the Aldol reaction product or the α, β-unsaturated aldehyde, but in a number of cases just only the α,β-unsaturated carbonyl product is acquired, particularly while extended conjugation is possible. The Aldol reaction is best performed with aldehydes. A number of ketones will go through an Aldol reaction, although equilibrium is set up among the products and starting materials and it is essential to remove the product as it is being created in order to pull the reaction through to completion.