The unstable intermediate dichlorocarbene $\left[: \mathrm{CCl}_{2}\right]$ is formed during

• A

  Kolbe's reaction
• B

  Friedel-Crafts reaction
• C

  Williamson synthesis
• Correct answer
  D

  Reimer-Tiemann reaction

Solution

The unstable intermediate $\left[: \mathrm{CCl}_{2}\right]$ is formed in Reimer-Tiemann reaction which is an electrophilic substitution reaction and occurs through the following steps. (i) Generation of electrophile

(ii) Electrophilic substitution

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