Question

Which compound is an intermediate in the Strecker synthesis ( $RCHO$, $HCN$, $NH _3$) of amino acids?

Answer 1

Hint : Strecker synthesis is a method employed for the synthesis of amino acids. The intermediate formed in strecker synthesis is an aminonitrile. An example for strecker synthesis is the synthesis of a derivative of L-valine from methyl isopropyl ketone.

Complete Step By Step Answer:
An aldehyde reacts with ammonium chloride in the presence of Potassium cyanide to give amino acids and this reaction is called strecker synthesis. This is a condensation reaction in which a water molecule is eliminated to yield alpha aminonitriles that give the desired amino acid on hydrolysis. Use of ketones instead of aldehydes give disubstituted amino acids.
Thus, Strecker synthesis is the synthesis of amino acids through hydrolysis of the nitrile, in which alpha aminonitriles are prepared as the intermediates.
Therefore, the correct option is C.

Additional Information:
In the first part of the reaction, the carbonyl oxygen of the aldehyde group is protonated. Then the carbonyl carbon is attacked by ammonia which is a nucleophile. After successive proton exchange, water is cleaved from the iminium ion intermediate. An aminonitrile is produced by the attack of cyanide ions on the iminium carbon.
In the second part of the synthesis, the nitrile nitrogen of the aminonitrile is protonated and a water molecule attacks the nitrile carbon. After subsequent proton exchange and nucleophilic attack of water on the former nitrile carbon, a $1,2 -$ diamino diol is formed. After the protonation of the amino group, ammonia is eliminated, and finally the hydroxyl group is deprotonated to produce an amino acid. This is the mechanism of Strecker synthesis.

Note :
In the asymmetric Strecker synthesis, the chiral variant of oligoethylene glycol is used as the catalyst and $KCN$ is used to generate a chiral cyanide ion. Strecker synthesis was discovered by Adolph Strecker. Strecker synthesis takes place in two stages where the aminonitrile is formed in the first stage.