53E - Organic Chemistry (Mcmurry)

Question

When an optically active carboxylic acid such as (R)-2-phenylpropanoic acid is brominated under Hell–Volhard–Zelinskii conditions, is the product optically active or racemic? Explain.

Step-by-Step Solution

Answer

The compound, (R)-2-phenylpropanoic acid is brominated under Hell–Volhard–Zelinskii conditions produces racemic mixture.

Step 1: The overall reaction

The overall reaction involves the reaction between a carboxylic acid and Br₂/PBr₃ followed by hydrolysis. This forms an alpha bromo carboxylic acid.

                                                          The overall reaction

Step 2: Mechanism of Hell-Volhard-Zelinskii reaction

The mechanism of Hell-Volhard-Zelinskii reaction with (R)-2-phenylpropanoic acid is as follows,

                                                        HVZ reaction

 

Bromination of (R)-2-phenylpropanoic acid produces racemic mixture of 2-bromo-2-phenylpropanoic acid.

                                              Formation of racemic mixture