Q35E - Organic Chemistry (Mcmurry)

Question

Amino acids can also be prepared by a two-step sequence that involves Hell–Volhard–Zelinskii reaction of a carboxylic acid followed by treatment with ammonia. Show how you would prepare leucine, (CH₃)₂CHCH₂CH(NH₂)CO₂H, and identify the mechanism of the second step.

Step-by-Step Solution

Answer

In the process of formation of leucine, a carboxylic acid undergoes a Hell-Volhard-Zelinskii reaction followed by ammonia.

Step 1: Preparation of leucine

In the process of formation of leucine, a carboxylic acid undergoes a Hell-Volhard-Zelinskii reaction followed by ammonia.

The preparation is,

                                                 HVZ-reaction

Step 2: Explanation

In the first step, the alpha hydrogen atom is substituted with bromide ion. Then the carboxylic –OH group is replaced with –Br atom.

Thus, the carboxylic acid group is protected.

Then, ammonia reacts with the bromide in the alpha position and forms the required product that is leucine.