Question

The reagent used in Sandmeyer reaction for converting benzene diazonium chloride into chlorobenzene is:

• A. \( CuCl/HCl \)
• B. \( NaCl \)
• C. \( Cl_2/FeCl_3 \)
• D. \( SOCl_2 \)

Hint:

Sandmeyer reactions use cuprous salts: \[ CuCl,\ CuBr,\ CuCN \] to replace diazonium groups with halogens or cyanide.

Answer 1

The Correct Option is A

Concept:
Sandmeyer reaction is an important substitution reaction of diazonium salts where the diazonium group is replaced by halogens or cyanide using cuprous salts. General reaction: \[ ArN_2^+Cl^- \xrightarrow{CuX} ArX \] where: \[ X = Cl,\ Br,\ CN \]

Step 1: Write the given transformation.
Benzene diazonium chloride: \[ C_6H_5N_2^+Cl^- \] must be converted into chlorobenzene: \[ C_6H_5Cl \]

Step 2: Identify appropriate Sandmeyer reagent.
For replacement by chlorine: \[ CuCl/HCl \] is used. Reaction: \[ C_6H_5N_2^+Cl^- \xrightarrow{CuCl/HCl} C_6H_5Cl + N_2 \] Nitrogen gas escapes, driving the reaction forward.

Step 3: Analyze incorrect options.

• \( NaCl \) cannot replace diazonium group.
• \( Cl_2/FeCl_3 \) is used for electrophilic chlorination.
• \( SOCl_2 \) converts alcohols into alkyl chlorides. Therefore the correct reagent is: \[ \boxed{CuCl/HCl} \]