My book states that:
Finkelstein reaction is particularly useful for preparing iodoalkanes. The iodoalkanes are obtained by heating chloro or bromoalkanes with a concentrated solution of sodium iodide in dry acetone.
$$\ce{R-X~+~NaI->[\ce{acetone,~reflux}]R-I~+NaX}$$ $(\ce{X=Cl,~Br;~R=alkyl ~group})$
Sodium chloride and sodium bromide being less soluble in acetone get precipitated from the solution and can be removed by filtration. This also prevents the backward reaction to occur according to Le Chartelier's principle. The reaction gives the best results with primary halides.
My question:
Can we prepare alkyl fluoride (not aryl fluoride) by Finkelstein reaction?
My book mentions about another reaction called Swarts reaction, through which alkyl fluoride is prepared. In Swarts reaction, alkyl fluorides are prepared by heating alkyl chlorides or bromides with salts such as mercurous fluoride ($\ce{Hg2F2}$), silver fluoride ($\ce{AgF}$), cobalt fluoride ($\ce{CoF3}$) or antimony trifluoride ($\ce{SbF3}$). Why can't we prepare alkyl fluoride by treating sodium fluoride with alkyl halide (Finkelstein reaction)?