The Finkelstein Reaction involves the substitution of a halogen atom in an alkyl halide with another halogen atom via an SN2 reaction, using acetone and a metal halide salt. The driving force behind the reaction is the lower solubility of the newly formed metal halide salt in acetone compared to the original one, shifting the equilibrium forward according to Le Chatelier’s principle.

This reaction is named after the German chemist Hans Finkelstein.

• Reagents: Acetone, metal halide salt

• Reactant: Alkyl halide

• Product: Substituted derivative

• Reaction Type: SN2

Experimental Tips:

• Alkyl bromides, alkyl chlorides, tosylates, and mesylates are readily converted into the corresponding alkyl iodides, which are often difficult to synthesize by other methods. [1]

• Alkyl fluorides are generally unreactive in SN2 reactions due to their high stability. One method to replace the fluorine atom with iodide involves the use of trimethylsilyl iodide (TMSI). [2]

• Primary, secondary, allylic, and benzylic halides are the most suitable substrates. In the presence of Lewis acids (e.g., AlMe₃, ZnCl₂, FeCl₃), NaI/CS₂ can be used to convert sterically hindered secondary and tertiary alkyl halides into alkyl iodides. [3]

• α-Haloketones and α-haloacids also undergo this reaction readily. [1]

• High-pressure microwave irradiation can accelerate the reaction. [4]

Reaction Mechanism:

Mechanism of the SN2 halogen exchange in the Finkelstein reaction.

Original Literature:
Finkelstein, H. Darstellung Organischer Jodide Aus Den Entsprechenden Bromiden Und Chloriden. Berichte der deutschen chemischen Gesellschaft, 1910, 43 (2), 1528–1532.

Key References:

• Nickel-Catalyzed Aromatic Finkelstein Reaction of Aryl and Heteroaryl Bromides, Chem. Commun., 2012, 48 (33), 3993–3995.

• Copper-Catalyzed Halogen Exchange in Aryl Halides: An Aromatic Finkelstein Reaction, J. Am. Chem. Soc., 2002, 124 (50), 14844–14845.

• Photo-Induced Metal-Catalyst-Free Aromatic Finkelstein Reaction, J. Am. Chem. Soc., 2015, 137 (26), 8328–8331.