Phenol - Reimer-Tiemann reaction

 Reimer-Tiemann reaction:
When phenol is refluxed with chloroform in the presence of acqueous sodium hydroxide at 340 K followed by hydrolysis, an aldehydic group (HC=O) gets introduced in the ring at a position ortho to the phenolic group. So ortho hydroxy bezaldehyde is formed. It is also called salicylaldehyde.