Write a note on Kolbe's reaction.

(N/A) Kolbe's reaction is a chemical reaction used to synthesize salicylic acid from phenol.
$1$. Phenol is treated with sodium hydroxide $(NaOH)$ to form sodium phenoxide.
$2$. Sodium phenoxide is then reacted with carbon dioxide $(CO_2)$ at a temperature of $398 \ K$ and a pressure of $4-7 \ bar$.
$3$. This leads to the formation of sodium salicylate,which upon acidification with concentrated hydrochloric acid $(HCl)$ yields salicylic acid ($2$-hydroxybenzoic acid).
Reaction sequence:
$C_6H_5OH + NaOH \rightarrow C_6H_5ONa + H_2O$
$C_6H_5ONa + CO_2 \xrightarrow{398 \ K, 4-7 \ bar} C_6H_4(OH)COONa$
$C_6H_4(OH)COONa + H^+ \rightarrow C_6H_4(OH)COOH$ (Salicylic acid)