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

• A

  $\mathrm{CO}_2, 6 \mathrm{~atm} \mathrm{H}_3 \mathrm{O}^{+}$
• Correct answer
  B

  $\mathrm{CHCl}_3$, aq. $\mathrm{NaOH}, \mathrm{H}_3 \mathrm{O}^{+}$
• C

  $\mathrm{CS}_2$ (at low temperature)
• D

  $\mathrm{Na}_2 \mathrm{Cr}_2 \mathrm{O}_7 / \mathrm{H}_2 \mathrm{SO}_4$

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.

Hence, the correct answer is option: 'B'.