Question

The two reactions involved in the conversion of benzene diazonium chloride to biphenyl are respectively

• A. Swarts, Fittig
• B. Gattermann, Swarts
• C. Sandmeyer, Wurtz
• D. Sandmeyer, Fittig

Hint:

In organic synthesis, biphenyl can be prepared using the Sandmeyer reaction (to obtain aryl halides) followed by the Fittig reaction (coupling of aryl halides using sodium in dry ether). This method is commonly used for biphenyl and other aromatic coupling reactions.

Answer 1

The Correct Option is D

The conversion of benzene diazonium chloride to biphenyl involves two critical reactions. To break down these reactions:

1. Sandmeyer Reaction: This reaction is utilized to transform benzene diazonium chloride into chlorobenzene. The process involves the use of copper(I) chloride (CuCl) as a catalyst, resulting in the substitution of the diazo group by a chlorine atom:
   C₆H₅N₂Cl + CuCl → C₆H₅Cl + N₂ + CuCl
2. Fittig Reaction: Subsequently, chlorobenzene undergoes the Fittig reaction, which is a coupling reaction using sodium (Na) in an ether medium. This reaction helps in forming biphenyl through the coupling of two chlorobenzene molecules:
   2C₆H₅Cl + 2Na → C₆H₅-C₆H₅ + 2NaCl

Combining these steps provides the pathway for converting benzene diazonium chloride to biphenyl, confirming that the correct pair of reactions is Sandmeyer followed by Fittig.

Answer 2

Step 1: Understanding the conversion of benzene diazonium chloride to biphenyl
The conversion of benzene diazonium chloride to biphenyl (\( C_6H_5 - C_6H_5 \)) involves two key reactions:
1. Sandmeyer Reaction:
- This reaction replaces the diazonium group (-\( N_2^+ \)) with a halogen (Cl, Br, I) using a copper(I) halide catalyst (\( CuX \)).
- In this case, benzene diazonium chloride reacts with CuCl to form chlorobenzene (\( C_6H_5Cl \)).
2. Fittig Reaction:
- This reaction is similar to the Wurtz reaction but involves aryl halides.
- Two molecules of chlorobenzene undergo coupling in the presence of sodium metal in dry ether, forming biphenyl (\( C_6H_5 - C_6H_5 \)).
Step 2: Examining the given options
- Option 1 (Swarts, Fittig) → Incorrect, as Swarts reaction is used for halogen exchange and is not involved in this conversion.
- Option 2 (Gattermann, Swarts) → Incorrect, as Gattermann reaction involves formylation of benzene derivatives, which is unrelated to biphenyl formation.
- Option 3 (Sandmeyer, Wurtz) → Incorrect, as Wurtz reaction applies to alkyl halides, not aryl halides.
- Option 4 (Sandmeyer, Fittig) → Correct, as these two reactions successfully convert benzene diazonium chloride to biphenyl.
Step 3: Conclusion
Since the correct sequence involves Sandmeyer reaction (for halogen substitution) followed by the Fittig reaction (for biphenyl formation), the answer is Option (4).