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Question: Which of the following method(s) does work for the preparation of secondary amine? $\square$ R-NO$_...

Which of the following method(s) does work for the preparation of secondary amine?

□\square R-NO2→SnCl2/HCl_2 \xrightarrow{SnCl_2/HCl}

□\square R-C-NH-R' →LiAlH4\xrightarrow{LiAlH_4}

□\square RNC →Ni/H2Δ\xrightarrow{\substack{Ni/H_2 \\ \Delta}}

□\square R-NO →NH3,H2S\xrightarrow{NH_3,H_2S}

A

R-NO2→SnCl2/HCl_2 \xrightarrow{SnCl_2/HCl}

B

R-C-NH-R' →LiAlH4\xrightarrow{LiAlH_4}

C

RNC →Ni/H2Δ\xrightarrow{\substack{Ni/H_2 \\ \Delta}}

D

R-NO →NH3,H2S\xrightarrow{NH_3,H_2S}

Answer

2, 3

Explanation

Solution

Let's analyze each reaction to determine if it produces a secondary amine.

  1. R-NO2→SnCl2/HCl_2 \xrightarrow{SnCl_2/HCl}:
    This reaction involves the reduction of a nitro compound (R-NO2_2). Nitro compounds are typically reduced to primary amines (R-NH2_2). For example: R−NO2→SnCl2/HClR−NH2R-NO_2 \xrightarrow{SnCl_2/HCl} R-NH_2 This method yields a primary amine.

  2. R-C(=O)-NH-R' →LiAlH4\xrightarrow{LiAlH_4}:
    This reaction involves the reduction of an N-substituted amide (a secondary amide) using Lithium Aluminium Hydride (LiAlH4_4). LiAlH4_4 is a strong reducing agent that reduces the carbonyl group (C=O) of amides to a methylene group (CH2_2), while retaining the carbon-nitrogen bond. For example: R−C(=O)−NH−R′→LiAlH4R−CH2−NH−R′R-C(=O)-NH-R' \xrightarrow{LiAlH_4} R-CH_2-NH-R' The product is an amine where the nitrogen atom is bonded to two alkyl/aryl groups (R-CH2_2 and R'), making it a secondary amine. This method yields a secondary amine.

  3. RNC →Ni/H2\xrightarrow{Ni/H_2}:
    This reaction involves the catalytic hydrogenation of an isocyanide (RNC), also known as a carbylamine. Isocyanides are reduced by hydrogen in the presence of a catalyst like Nickel (Ni) to form secondary amines. The carbon-nitrogen triple bond in isocyanides (R-N≡C) is hydrogenated, adding hydrogen to both carbon and nitrogen. For example: R−N≡C→Ni/H2R−NH−CH3R-N\equiv C \xrightarrow{Ni/H_2} R-NH-CH_3 The product is an amine where the nitrogen atom is bonded to two alkyl/aryl groups (R and CH3_3), making it a secondary amine. This method yields a secondary amine.

  4. R-NO →NH3,H2S\xrightarrow{NH_3,H_2S}:
    This reaction involves the reduction of a nitroso compound (R-NO). Reduction of nitroso compounds, especially aromatic ones, by reagents like ammonium sulfide ((NH4_4)2_2S, which is equivalent to NH3_3/H2_2S) typically yields primary amines. For example: C6H5−NO→NH3,H2SC6H5−NH2C_6H_5-NO \xrightarrow{NH_3, H_2S} C_6H_5-NH_2 This method yields a primary amine.

Based on the analysis, methods 2 and 3 work for the preparation of secondary amines.