Hunsdiecker reaction template

Silver propanoate and bromine form an acyl hypobromite; its O–Br bond breaks homolytically, the carboxyl radical loses CO₂ and the ethyl radical takes Br in a chain to give bromoethane.

Mechanism step by step

A silver carboxylate and Br₂ give an alkyl bromide with one carbon fewer

1. Acyl hypobromite – Carboxylate O attacks Br₂; Ag⁺ pulls off bromide as AgBr
2. Initiation – The weak O–Br bond breaks evenly on heating
3. Decarboxylation – The carboxyl radical loses CO₂: an ethyl radical
4. Propagation – The ethyl radical takes Br from the hypobromite, regenerating the carboxyl radical

Key points

• The product has one carbon fewer than the acid: a decarboxylative bromination.
• Fish-hook arrows move one electron each; propagation keeps the number of radicals.
• The silver salt must be dry; AgBr precipitating drives the first step.
• Yield order of the alkyl group: 1° > 2° > 3°. Cl₂ also works; I₂ gives esters (Simonini).

Drawn with 70 atoms, 15 arrows, 9 shapes – every one editable in MolDraw.

Sources

• Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005 Textbook
• Smith, March's Advanced Organic Chemistry, 8th ed., Wiley 2020 Textbook