Consider the following chemical reaction and identify the intermediate involved in the reaction.
Show Hint
Phenol going to salicylaldehyde is the Reimer-Tiemann reaction (CHCl\(_3\) with aqueous NaOH). Find the species formed after the dichlorocarbene attacks the phenoxide ring.
Step 1: Understanding the Question.
The question gives phenol on the left and salicylaldehyde on the right. We must pick the species that sits between them.
A CHO group added at the ortho position of phenol points to the Reimer-Tiemann reaction.
Step 2: Work backwards from the product.
The CHO group in the product can come from hydrolysis of a CHCl$_2$ group. In base, a carbon with two chlorine atoms and one hydrogen turns into an aldehyde.
So the species just before the product must carry CHCl$_2$ at the ortho position.
The reaction is run in aqueous NaOH, so the oxygen of this species is present as the sodium salt, O-Na$^+$.
Step 3: Work forwards from phenol to confirm.
Phenol + NaOH gives phenoxide. CHCl$_3$ + NaOH gives dichlorocarbene $:CCl_2$.
The ring carbon next to the O-Na$^+$ carbon attacks the carbene, which puts a CHCl$_2$ group at the ortho position.
This gives the ortho CHCl$_2$ phenoxide, which is later hydrolysed to the aldehyde.
Step 4: Match with the options.
Option (1) has CHO already, so it is a later stage, not the intermediate.
Option (3) has a free OH, but the medium is strongly basic, so the phenoxide form must be shown.
Option (4) has CH$_2$Cl, which has only one chlorine and cannot come from a carbene with two chlorines.
Only option (2), with O-Na$^+$ and CHCl$_2$, fits both the forward and the backward route.
Final Answer:
Option (2) is the intermediate of the Reimer-Tiemann reaction.
\[ \boxed{\text{Option (2)}} \]
