Question

What happens when Aldols readily lose water?

Answer 1

1. Aldol is a short term used for aldehyde and alcohol.
2. Aldol is a product formed when two carbonyl compounds join together to form a $\mathrm{\beta }$-hydroxy-carbonyl product where one acts as a nucleophilic donor (enol or enolate ion) and the other acts as an electrophilic acceptor.

Mechanism: Aldol Formation

• When an aldol product readily loses water it forms $\mathrm{\alpha }-\mathrm{\beta }$unsaturated carbonyl compounds. $\mathrm{\beta }-$hydroxy aldehydes or aldol and $\mathrm{\beta }-$hydroxy ketone or ketal lose the water molecule easily to form enal or enone. This is called Aldol Condensation. For example$$\begin{gathered} 2{\mathrm{CH}}_3\mathrm{CHO}\left(\mathrm{l}\right)\hspace{0.17em}\stackrel{\mathrm{dil}\mathrm{NaOH}}{\rightleftharpoons }{\mathrm{CH}}_3{\mathrm{CHOHCH}}_2\mathrm{CHO}\left(\mathrm{l}\right)\stackrel{-{\mathrm{H}}_2\mathrm{O}}{\rightleftharpoons }{\mathrm{CH}}_3\mathrm{CH}=\mathrm{CHCHO}\left(\mathrm{l}\right) \\ \mathrm{Ethanal}3-\mathrm{hydroxy}\mathrm{butanal}\mathrm{But}-2-\mathrm{enal} \\ (\mathrm{Aldol}\mathrm{product})(\mathrm{Aldol}\mathrm{condensation}) \end{gathered}$$
• Since, the aldehyde is a better electrophile than ketone (less steric hindrance) so it minimizes products from the self reaction from the ketone. It readily loses water molecule and undergo aldol condensation.