c
Reaction of phenol with chloroform in presence of dilute sodiute sodium hydroxide finally introduces aldehyde \(-CHO \) functional group and hydroxy group at-ortho position. The reaction is known as Reimer-Tiemann reaction.

\(C_{6} H_{5} O H \frac{a q^{N a O H}}{C H C l_{3}} 2-O H-C_{6} H_{4}-C H O\)