Question

The reagent ‘R’ in the given sequence of chemical reaction is

• A. CuCN/KCN
• B. H₂O
• C. CH₃CH₂OH
• D. HI

Answer 1

The Correct Option is C

To determine the reagent ‘R’ in the given chemical reaction sequence, we need to analyze the transformation from the starting material to the product.

The reaction sequence starts with a diazonium salt formation from an aniline derivative using \text{NaNO}_2 and \text{HCl} at 0^\circ \text{C}. This converts the -NH₂ group to a diazonium group (-N⁺₂Cl^-).

The next step involves replacement of the diazonium group with a hydrogen atom. This type of transformation can be achieved by reduction, often using ethanolic solvents. Among the given options, CH₃CH₂OH (ethanol) is commonly used as the solvent and reagent in reductive decomposition of diazonium salts. This process leads to the formation of the final product by replacing the diazonium group with a hydrogen atom.

Now, let's analyze the options:

• CuCN/KCN: Used for introducing a cyano group (-CN), not suitable here.
• H₂O: Would lead to the formation of phenol, not the desired reaction.
• CH₃CH₂OH (Correct Answer): Suitable for reducing diazonium salts to replace with hydrogen.
• HI: Not relevant to this type of reaction.

The reagent ‘R’ is thus CH₃CH₂OH, confirming the transformation from the diazonium salt to the desired bromo-benzene derivative.