4-Bromobenzaldehyde

4-Bromobenzaldehyde, or p-bromobenzaldehyde, is an organobromine compound with the formula BrC6H4CHO. It is one of three isomers of bromobenzaldehyde. 4-Bromobenzaldehyde is a colorless liquid. It displays reactivity characteristic of benzaldehyde and an aryl bromide.

Preparation
4-Bromobenzaldehyde may be prepared in the laboratory in two steps by oxidation 4-bromotoluene. In the first step, two bromine atoms are added to the methyl group of 4-bromotoluene by free radical bromination to form 4-bromobenzal bromide. In the second step, the dibrominated methyl group is hydrolyzed with calcium carbonate, then steam distilled to collect 4-bromobenzaldehyde.

Reactions
Owing to the bromoaryl group, 4-bromobenzaldehyde participates in various cross coupling reactions, such as Suzuki coupling. In a Sonogashira coupling it couples with trimethylsilylacetylene to form 4-((trimethylsilyl)ethynyl)benzaldehyde, precursor to 4-ethynylbenzaldehyde.