Question

The radical-chain reaction in the Hunsdiecker reaction is:

• A. the homolytic cleavage of the relatively weak carbon-bromine bond
• B. the homolytic cleavage of the relatively weak oxygen-bromine bond
• C. the hetrolytic cleavage of the relatively weak oxygen-bromine bond
• D. none of these

Answer 1

Answer: (B)

the homolytic cleavage of the relatively weak oxygen-bromine bond

Hunsdiecker reaction is a halogenation reaction. The reaction mechanism of the Hunsdiecker reaction is believed to involve organic radical intermediates. The silver salt of the carboxylic acid 1 will quickly react with bromine to form acyl hypohalite intermediate via homolytic cleavage of weak oxygen-bromine bond 2. Formation of the diradical pair 3 allows for radical decarboxylation to form the diradical pair 4, which will quickly recombine to form the desired organic halide 5. The trend in the yield of the resulting halide is primary > secondary > tertiary.