PROBLEM 25.8 - Organic Chemistry

Question

Question: What alkyl halide is needed to prepare each 1° amine by a Gabriel synthesis?

a.

b.

c.

Step-by-Step Solution

Answer

Answer

a.

Starting material for heptanamine

b.

Starting material for 3-methyl butanamine

c.

Starting material for 2-(3-methoxycyclohexyl)ethanamine.

Synthesis of amines

Amines are Lewis bases. The Amine group is nucleophilic and therefore amines are primarily prepared by nucleophilic addition or substitution reactions.

For example, halides on substitution with ammonia or ammonia derivatives give amines.

The reduction of other nitrogen-containing compounds like amides, nitriles, and nitro compounds also gives amines.

 

Gabriel synthesis

Haloalkanes on reaction with ammonia give amines and halogen acids. This reaction for the synthesis of amines is called Gabriel synthesis.

The reaction is a two-step process- nucleophilic substitution followed by hydrolysis.

To find the starting material for amine synthesized by Gabriel synthesis, the amino group is replaced by the halogen group.

Starting material for the given amines

a. The given amine is heptanamine. Replacing the amino group, the halide used will be bromoheptane

Retro analysis of heptanamine

b.The given amine is 3-methyl butanamine. Replacing the amino group, the starting material is 3-methyl bromobutane.

Retroanalysis of 3-methyl butanamine

c.The given compound is 2-(3-methoxycyclohexyl)ethanamine. Replacing the amino group, the starting material is 2-(3-methoxycyclohexyl) bromoethane.

Retro analysis of 2-(3-methoxycyclohexyl)ethanamine.