The synthesis of alkyl fluorides is best accomplished by the Swarts reaction. This reaction involves the conversion of alkyl chlorides or bromides into alkyl fluorides by heating them with metallic fluorides such as silver fluoride (AgF), mercurous fluoride (Hg₂F₂), or cobalt fluoride (CoF₃). The reaction proceeds via a nucleophilic substitution mechanism where fluoride ion replaces the chloride or bromide ion.

The general reaction can be represented as:

where R is an alkyl group, X is Cl or Br, and M is a metal like Ag, Hg, or Co.

This method is preferred because direct fluorination using F₂ is highly exothermic and difficult to control, often leading to side reactions such as carbon chain fragmentation. The Swarts reaction provides a controlled and efficient way to produce alkyl fluorides.

Now, let's evaluate the other options:

• Finkelstein reaction: This is used to prepare alkyl iodides or bromides by exchanging chloride with iodide or bromide using NaI or NaBr in acetone. It does not produce fluorides.
• Free radical fluorination: Direct fluorination with F₂ is highly violent and non-selective, making it unsuitable for controlled synthesis.
• Sandmeyer's reaction: This is used to synthesize aryl halides from diazonium salts, not alkyl fluorides.

Thus, the correct choice is the Swarts reaction.

Related Topics

Nucleophilic Substitution Reactions: These involve the replacement of a leaving group by a nucleophile. The Swarts reaction is an example of this, where fluoride acts as the nucleophile.

Preparation of Haloalkanes: Various methods exist for synthesizing different haloalkanes, such as Finkelstein for iodides/bromides, and Swarts for fluorides.

Important Formulae

Swarts Reaction Equation: