well a colleage was having a problem getting this reaction to go to completion using potassium iodide as the iodide source as oppsosed to sodium iodide as the iodide source and he pointed out rather correctly that sodium iodide is about 35-40 times more soluble in acetone than potassium iodide.
Hence, the reason sodium iodide is the preffered salt used in these reactions.
So i was put in a corner having to defend myself that yes it does indeed work with potassium iodide.
it requires good mechanical stirring (he shook his mix approx 15 minutes) the minimal time to run this reaction is 30 minutes if not more.
but i came across some good reading as to why this reactions proceeds that you all might find interesting,

http://www.ch.ic.ac.uk/rzepa/blog/?p=439

'the mystery of the finkelstein reaction'
and also a SM thread that sort of backs of the veracity of potassium iodide working in spite of it's lower solubiity in acetone.

http://www.sciencemadness.org/talk/viewthread.php?tid=12205

also it is important to point out that the relative rates of reaction for primary vs. secondary alkyl chlorides are 1 to .0179

electron donating groups like double bonds and aromatic rings increase this rate so benzyl chloride/bromide would react faster than it's alkyl counterpart.
in the case of methylenedioxyphenyl-2-bromopropane there may be some inductive effect considering the ring has two activating groups, i don't know.


the thread ends with an unintelligent noob question  don't they all?

i'm not sure i think it is because it's isolated in it's natural state as a potassium salt.
any modifications of this reaction are welcome in this thread for examle aromatic substitution with nai and catalyzed by cuppric iodide it is'nt a finkelstein reaction per se but the idea is similar.

The cynic in me would say it's because iodide is expensive and the molar weight of potassium is 1.7x that of sodium.

That is a point, how well does your colleage know chemistry? Hes not just trying to plug KI in for NaI is he?

Incomplete reaction is my point. Did this fellow just attempt to add the same weight of KI instead of NaI not paying attention to molar ratios of avalible iodine?

I've used KI and had an almost complete conversion using 2-bromosafrole. Confirmed using TLC, slight spotting, shaken mechanically for 45min (probably could have left it on longer). Due to solubility NaI works much faster but each gets the job done just as well.