To avoid mixing up Kolbe's and Reimer-Tiemann reactions, remember:
\(\text{CO}_2\) has 2 oxygens \(\rightarrow\) gives an acid (Salicylic acid, \(\text{-COOH}\))
\(\text{CHCl}_3\) has no oxygen \(\rightarrow\) introduces an aldehyde group (Salicylaldehyde, \(\text{-CHO}\))
Step 1: Understanding the Concept:
This problem requires knowledge of the standard chemical reactions of phenol. Phenol undergoes characteristic substitution and oxidation/reduction reactions depending on the reagents used. Step 2: Key Formula or Approach:
The approach involves identifying the specific name reaction or standard transformation for each of the three pathways provided in the reaction scheme. Step 3: Detailed Explanation:
Let's analyze the three distinct reactions of phenol: Reaction 1: Formation of A
\(\text{Phenol} \xrightarrow{\text{NaOH, CO}_2} \text{Product A}\)
- This specific combination of reagents corresponds to the Kolbe's reaction (or Kolbe-Schmitt reaction).
- Phenol reacts with sodium hydroxide to form sodium phenoxide, which is even more reactive towards electrophilic aromatic substitution.
- It then reacts with the weak electrophile, carbon dioxide (\(\text{CO}_2\)), under pressure and heat.
- Acidification yields the final main product, which is 2-hydroxybenzoic acid, commonly known as Salicylic acid.
- This matches Structure A in the options. Reaction 2: Formation of B
\(\text{Phenol} \xrightarrow{\text{Zn dust, } \Delta} \text{Product B}\)
- When phenol is heated with zinc dust, it undergoes a reduction reaction.
- The zinc acts as a reducing agent, abstracting the oxygen from the phenol to form zinc oxide (\(\text{ZnO}\)), while the aromatic ring is reduced to Benzene (\(\text{C}_6\text{H}_6\)).
- This matches Structure B in the options. Reaction 3: Formation of C
\(\text{Phenol} \xrightarrow{\text{Na}_2\text{Cr}_2\text{O}_7, \text{H}_2\text{SO}_4} \text{Product C}\)
- Sodium dichromate (\(\text{Na}_2\text{Cr}_2\text{O}_7\)) in acidic medium is a strong oxidizing agent.
- Phenol is easily oxidized by chromic acid. The oxidation disrupts the aromaticity to produce a conjugated diketone.
- The product is cyclohexa-2,5-diene-1,4-dione, which is universally known as p-Benzoquinone.
- This matches Structure C in the options. Step 4: Final Answer:
By systematically solving the reactions, we find that A is Salicylic acid, B is Benzene, and C is p-Benzoquinone, which correspond precisely to the provided options A, B, and C.
