Write a note on Reimer-Tiemann reaction.

(N/A) The Reimer-Tiemann reaction is a chemical reaction used for the ortho-formylation of phenols.
When phenol is treated with chloroform $(CHCl_3)$ in the presence of an aqueous base like sodium hydroxide $(NaOH)$,a formyl group $(-CHO)$ is introduced at the ortho position of the benzene ring.
This reaction proceeds through the formation of a substituted benzal chloride intermediate,which upon hydrolysis with $NaOH$ followed by acidification with $HCl$,yields salicylaldehyde ($2$-hydroxybenzaldehyde).
The overall reaction can be represented as:
$C_6H_5OH + CHCl_3 + 3NaOH \rightarrow C_6H_4(OH)CHO + 3NaCl + 2H_2O$.