Why is it important to use dry tubes for the reactinos involving sodium iodide in acetone? (SN2 reaction..)

Question

This is organic chem experiment question.

quick answer needed . Thanks! I think if tube is not dry, water would make the solvent polar protic instead of aprotic? preventing SN2 to happen? thanks for your answer.

Answer 1

The Finkelstein reaction NaI + R-Br/Cl  ----   R-I  + NaBr/Cl takes advantage of the fact that all the halides of Na+ except NaI are NOT soluble in acetone. This means that the reaction is shifted to the right because the formation of the alkyl iodide is accompanied by the precipitation of NaBr/Cl.  If water is present , the salts are now much more soluble in the medium and thus the reaction will not proceed to completion. NaBR and NaCl are more soluble in aqueous acetone.

Answer 2

You answered it.