Question

What aldehyde is needed to synthesize each amino acid by the Strecker synthesis?

(a) Valine;

(b) Leucine;

(c) Phenylalanine.

Short answer

(a)

(b)

(c)

Step-by-step solution

Strecker synthesis

In this method, aldehyde is taken with a mixture of ammonium chloride and $\text{KCN}$to form cyanohydrene which then react with excess ${\mathrm{NH}}_3$ and gives whichfurther undergoes hydrolysis to form $\mathrm{\alpha }$-amino acid.

Reagent

In these reactions, cyanohydrene is used as a chemical weapon agent in the reaction and excess of ammonia is used for the removal of hydrogen ion.

Reaction

(a) 2-methypropanaldehyde reacts with cyanohydrene and forms a compound which on reaction with excess ${\mathrm{NH}}_3$ ,a water molecule is removed and a-aminonitride is formed which on further hydrolysis gives valine.

Formation of valine

(b) 3-methylbutanaldehyde reacts with cyanohydrene and forms a compound, which on reaction with excess of ${\mathrm{NH}}_3$, a water molecule is removed and a-aminonitride is formed which on further hydrolysis gives leucine.

Formation of leucine

(c) Phenyl acetaldehyde reacts with cyanohydrene and forms a compound which on reaction with excess of ${\mathrm{NH}}_3$, a water molecule is removed and a - aminonitride is formed, which on further hydrolysis gives phenylalanine.

Formation of phenylalanine