Reduction of Nitro Compounds, Nitriles and Amides

Three independent starting materials all converge on a primary amine by simple

reduction:

Reduction of nitro compounds -- covered in detail in Section 25.3 -- takes

$\text{R}-\text{NO}_2$ through six electrons of reduction (via nitroso and hydroxylamine

intermediates when followed stepwise) to $\text{R}-\text{NH}_2$, using

$\text{Fe}/\text{HCl}$, $\text{Sn}/\text{HCl}$, or catalytic $\text{H}_2$.

Reduction of nitriles takes $\text{R}-\text{C}{\equiv}\text{N}$ to

$\text{R}-\text{CH}_2-\text{NH}_2$ using $\text{LiAlH}_4$ (or catalytic $\text{H}_2/\text{Ni}$,

sometimes called the Mendius reduction):

This route always installs ONE MORE carbon in the final amine than was present in the

original haloalkane used to make the nitrile in the first place (since $\text{R}-\text{X}

• \text{KCN} \to \text{R}-\text{CN}$ already added a carbon), a useful way to extend a carbon chain by exactly one unit while simultaneously installing the amine.

Reduction of amides takes $\text{R}-\text{CONH}_2$ to $\text{R}-\text{CH}_2-\text{NH}_2$

using $\text{LiAlH}_4$:

This must be carefully distinguished from the Hoffmann bromamide degradation of the SAME

starting amide (Section 25.5.4): $\text{LiAlH}_4$ reduction of an amide RETAINS the

carbonyl carbon (reducing $\text{C}=\text{O}$ down to $\text{CH}_2$, so the product amine …