Chapter 21, Problem 21.47P

Interpretation Introduction

(a)

Interpretation:

The complete mechanism and the major organic product of the given reaction are to be written.

Concept introduction:

In the reaction between a carboxylic acid and ${\text{PBr}}_{\text{3}}$ gives an acid bromide. In this reaction the bonds around the $\text{C=O}$ and C-OH are broken and $\text{C=O}$ and C-Br are formed. Therefore, the original carbon skeleton remains unchanged. Further ${\text{HOPBr}}_{\text{2}}$ takes H from the alpha carbon atom to form a resonance stabilized carbonyl group. Enol is formed at the alpha carbon takes place after bromination. Finally, the hydrolysis of acyl bromide forms a tetrahedral intermediate which on the reformation of carbonyl forms corresponding carboxylic acid.

Interpretation Introduction

(b)

Interpretation:

The complete mechanism and the major organic product of the given reaction are to be written.

Concept introduction:

In the reaction between a carboxylic acid and ${\text{PBr}}_{\text{3}}$ gives an acid bromide. In this reaction the bonds around the $\text{C=O}$ and C-OH are broken and $\text{C=O}$ and C-Br are formed. Therefore, the original carbon skeleton remains unchanged. Further ${\text{HOPBr}}_{\text{2}}$ takes H from the alpha carbon atom to form a resonance stabilized carbonyl group. Enol is formed at the alpha carbon takes place after bromination. Finally, the hydrolysis of acyl bromide forms a tetrahedral intermediate which on the reformation of carbonyl forms corresponding carboxylic acid.