Explain preparation of alkyl halides by halogen exchange methods.

Explanation

(i) Finkelstein Reaction : Alkyl iodides are often prepared by the reaction of alkyl chlorides or alkyl bromides with NaI in dry acetone.
`underset("Bromoethane")(CH_(3)-CH_(2)-Br)+NaI overset(" Acetone ")rarr underset("Iodoethane")(CH_(3)CH_(2))-I + NaBr`
`underset("Chloroethane")(CH_(3)CH_(2)Cl)+NaI overset(" Acetone ")rarr underset("Iodoethane")(CH_(3)CH_(2)I)+NaCl`
NaCl or NaBr thus formed is precipitated in dry acetone. It facilitates the forward reaction according to Le Chatelier.s Principle.
(ii) Swartz Reaction : The synthesis of alkyl fluorides is best accomplished by heating an alkyl chloride or alkyl bromide in the presence of a metallic fluoride such as `AgF, Hg_(2)F_(2), CoF_(2)` or `SbF_(3)`.
`H_(3)C-Br+AgF to H_(3)C-F+AgBr`.