Wohl–Ziegler bromination

Wohl–Ziegler Bromination is a chemical reaction that involves the bromination of alkenes to form allylic bromides. This reaction is significant in organic chemistry for the functionalization of alkenes, allowing for further chemical modifications. The Wohl–Ziegler Bromination is named after the chemists Alfred Wohl and Karl Ziegler, who developed the reaction.

Reaction Mechanism

The Wohl–Ziegler Bromination proceeds through a radical mechanism. The reaction is initiated by the decomposition of a bromine source, typically N-bromosuccinimide (NBS), in the presence of a radical initiator like azobisisobutyronitrile (AIBN) or benzoyl peroxide under light or heat. This generates bromine radicals, which abstract a hydrogen atom from the allylic position of the alkene, forming an allylic radical. The allylic radical then reacts with a bromine molecule to form the allylic bromide product.

Applications

The Wohl–Ziegler Bromination is widely used in organic synthesis for the preparation of allylic bromides. These compounds are valuable intermediates in various chemical transformations, including nucleophilic substitutions, eliminations, and cross-coupling reactions. The ability to selectively brominate allylic positions in the presence of other potentially reactive functional groups makes this reaction a powerful tool in the synthesis of complex organic molecules.

Advantages and Limitations

One of the main advantages of the Wohl–Ziegler Bromination is its high regioselectivity for the allylic position, which is often difficult to achieve with other bromination methods. However, the reaction conditions can sometimes lead to the formation of side products, such as dibrominated compounds or rearranged products, which can complicate the purification process. Additionally, the use of radical initiators and light or heat can pose safety concerns and requires careful handling.

Related Reactions

• Allylic Bromination: A general term for reactions that introduce bromine atoms at allylic positions of alkenes.
• N-Bromosuccinimide (NBS): A brominating agent commonly used in the Wohl–Ziegler Bromination and other bromination reactions.
• Radical Reactions: A class of chemical reactions involving radicals, which are species with unpaired electrons.

See Also

• Organic Synthesis
• Halogenation
• Alkene Functionalization

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  NBS allylic bromination scheme
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  Goldfinger and Bloomfield Mechanisms
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  Addition vs. Substitution