Which reagent from following is used in Reimer-Tiemann reaction?

Which reagent from following is used in Reimer-Tiemann reaction?
  1. $\mathrm{CO}_2, 6 \mathrm{~atm} \mathrm{H}_3 \mathrm{O}^{+}$
  2. $\mathrm{CHCl}_3$, aq. $\mathrm{NaOH}, \mathrm{H}_3 \mathrm{O}^{+}$
  3. $\mathrm{CS}_2$ (at low temperature)
  4. $\mathrm{Na}_2 \mathrm{Cr}_2 \mathrm{O}_7 / \mathrm{H}_2 \mathrm{SO}_4$

Solution

When phenol reacts with chloroform in the presence of bases $(\mathrm{NaOH} / \mathrm{KOH})$, an aldehyde $(-\mathrm{CHO})$ group gets introduced in the ring at a position ortho to the phenolic group and salicylaldehyde is formed. This reaction is called the Reimer-Tiemann reaction.

Asked in: MHT CET 2024 (11 May Shift 1)

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