Question

Ethylamine can be prepared by all except:

• A. Curtius reaction
• B. Hoffman bromamide reaction
• C. Gabriel Phthalimide reaction
• D. Reduction of formaldoxime

Answer 1

The correct option is D Reduction of formaldoxime

In Curtius reaction, first the conversion of acyl azide $(R-CO-N_3)$ into isocyanate $(R-N=C=O)$ takes place followed by its reaction with water to give primary amine $\left(RN{H}_2\right)$. So, for the preparation of ethyl amine,

$C_2{H}_5-CO-N=N^{+}=N^{-}\underset{-N_2}{\stackrel{\Delta }{\to }}{C}_2{H}_5-N=C=O\stackrel{H_{2}O}{\to }{C}_2{H}_5-N{H}_2$

Hoffmann bromamide reaction is the conversion of primary amide into primary amine with one carbon less. Primary amide reacts with bromine $\left(B{r}_2\right)$ and a base $\left(NaOH\right)$ to form an intermediate isocyanate $(R-N=C=O)$ which upon hydrolysis gives primary amine (with one carbon less) along with the evolution of $C{O}_2$ gas.

$C_2{H}_5-CO-N{H}_2\underset{NaOH}{\stackrel{B{r}_2}{\to }}{C}_2{H}_5-N=C=O\stackrel{H_{2}O}{\to }{C}_2{H}_5-N{H}_2$

Gabriel Phthalimide reaction involves the conversion of primary alkyl halides into primary amines. Phthalimide undergoes deprotonation and reacts with alkyl halide to form an intermediate which reacts with hydrazine to give primary amine as the final product.

Reduction of formaldoxime does not yield primary amine.