Salicylaldehyde is prepared by heating phenol and chloroform together in the presence of potassium hydroxide or sodium hydroxide. This reaction is called the Reimer-Tiemann reaction.
The Reimer Tiemann reaction is an organic chemical reaction where phenol is converted into an ortho hydroxy benzaldehyde using chloroform, a base, and an acid workup. This reaction can also be described as the chemical reaction used for the ortho-formylation of phenols.

