crotonaldehyde

Crotonaldehyde, or trans-2-butenal, is an alpha,beta-unsaturated aldehyde with the formula CH3-CH=CH-CHO. It exists mainly as the trans (E) isomer; the cis (Z) isomer is less common. It is a colorless to pale yellow liquid with a sharp, acrid odor. It is a reactive dienophile and a Michael acceptor.

Industrial production commonly proceeds by aldol condensation of acetaldehyde to give 3-hydroxybutanal, followed by dehydration to crotonaldehyde; it can also be obtained by oxidation of crotyl alcohol or as a byproduct in hydroformylation processes.

In organic synthesis, crotonaldehyde participates in 1,4-additions and other conjugate additions, owing to its conjugated aldehyde motif. It readily polymerizes in the absence of stabilizers. It can be hydrogenated to butanal or oxidized to crotonic acid; derivatives are accessible via further functionalization.

Uses of crotonaldehyde include serving as an intermediate for the manufacture of fine chemicals such as fragrances, flavors, and certain pharmaceutical building blocks. Its reactivity makes it a useful building block, but its toxicity and lachrymatory properties limit handling.

Safety and handling: Crotonaldehyde is a corrosive irritant to skin, eyes, and the respiratory tract. It is flammable and reacts with oxidizers; exposure is controlled by regulations. Stabilizers such as hydroquinone are used to inhibit polymerization, and handling typically requires ventilation, personal protective equipment, and closed systems.