chlorobenzaldehyde

Chlorobenzaldehyde refers to any of the three isomeric benzaldehydes that contain one chlorine substituent on the benzene ring. The isomers are 2-chlorobenzaldehyde (o-chlorobenzaldehyde), 3-chlorobenzaldehyde (m-chlorobenzaldehyde), and 4-chlorobenzaldehyde (p-chlorobenzaldehyde). They are generally colorless to pale yellow solids or liquids and possess the characteristic odor associated with many aldehydes. The aldehyde group is meta-directing in electrophilic substitution, so direct chlorination of benzaldehyde typically yields a mixture with a predominance of the meta isomer, along with smaller amounts of the ortho and para isomers; separation of the isomers is commonly required.

Synthesis of chlorobenzaldehydes is commonly accomplished by electrophilic chlorination of benzaldehyde under controlled conditions, which affords a mixture of isomers that can be separated by distillation or crystallization. Other methods include formylation of chlorinated benzenes (for example via Gattermann–Koch or related routes) to install the aldehyde group onto a chlorinated ring, which can provide access to specific isomers depending on the starting material and conditions.

Applications of chlorobenzaldehydes arise from the reactivity of both the formyl group and the chloro substituent. They serve as important building blocks in the synthesis of dyes, pigments, pharmaceuticals, agrochemicals, and fragrances. The aldehyde can participate in a range of reactions (nucleophilic additions, condensations, and cross-coupling after halogen substitution), while the chlorine atom enables further functionalization through nucleophilic substitution or metal-catalyzed coupling.

Safety considerations include handling as irritants to skin, eyes, and respiratory tract. They should be used in well-ventilated facilities with appropriate protective equipment and stored away from oxidizers.