Question

Which of the following reagents are used to prepare primary amines by Hoffmann bromamide degradation reaction ? \[ (i)\quad \begin{array}{c} O\\ || \end{array} R-C-NH_2 \] \[ (ii)\quad NaOH \] \[ (iii)\quad Br_2 \] \[ (iv)\quad CHCl_3 \]

• A. (i), (ii) and (iv)
• B. (i) and (iii)
• C. (i), (ii) and (iii)
• D. (i), (iii) and (iv)

Hint:

Hoffmann bromamide degradation converts an amide into a primary amine containing one carbon atom less. Always remember the reagents: \[ RCONH_2 + Br_2 + NaOH \] Amide + Bromine + Sodium hydroxide.

Answer 1

The Correct Option is C

Concept: Hoffmann bromamide degradation reaction, also known as Hoffmann bromamide reaction or Hoffmann rearrangement, is an important method for the preparation of primary amines from amides. In this reaction, an amide containing one carbonyl carbon is converted into a primary amine having one carbon atom less than the parent amide. The reaction involves the use of bromine and a strong base such as sodium hydroxide. During the reaction, the carbonyl carbon of the amide is lost as carbon dioxide, resulting in the formation of a primary amine. The general reaction is \[ RCONH_2 + Br_2 + 4NaOH \rightarrow RNH_2 + Na_2CO_3 + 2NaBr + 2H_2O \] Thus, the essential reagents are:

• Amide \((RCONH_2)\)

• Bromine \((Br_2)\)

• Sodium hydroxide \((NaOH)\)

Step 1: Identifying the reagents listed in the question. The reagents given are: \[ (i)\; RCONH_2 \] \[ (ii)\; NaOH \] \[ (iii)\; Br_2 \] \[ (iv)\; CHCl_3 \] We must determine which of these are required for Hoffmann bromamide degradation.

Step 2: Recalling the reaction conditions of Hoffmann bromamide degradation. The reaction proceeds according to \[ RCONH_2 + Br_2 + NaOH \longrightarrow RNH_2 \] Hence the required reagents are: \[ RCONH_2,\; Br_2,\; NaOH \] Therefore, \[ (i),\;(ii),\;(iii) \] are necessary.

Step 3: Checking whether chloroform is required. Chloroform \((CHCl_3)\) is not used in Hoffmann bromamide degradation. Instead, chloroform is commonly used in the Carbylamine reaction for preparing isocyanides. Hence, \[ CHCl_3 \] is not required.

Step 4: Selecting the correct option. The correct combination is \[ (i),\;(ii),\;(iii) \] which corresponds to Option (C). \[ \boxed{\text{Option (C)}} \]