Domo_Kun
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Finkelstein swap of DCM to DIM
If I was to run a Finkelstein reaction to get diiodomethane out of dichloromethane using NaI:
1. Does everything need to be in acetone solution?
2. Do I have to reflux, and if so, at what temperature and for how long?
3. What yeild should I expect?(how can this be calculated? something to do with the solubility of reactant/products?)
Thanks
[EDIT]
Also, would it be a problem if if there was sodium hydroxyde in the NaI?
[Edited on 30-10-2011 by Domo_Kun]
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ldanielrosa
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Thank you for the inspiration, I think I'll try something similar with NaBr and methanol.
1. Acetone is used because NaI is soluble in acetone, but NaCl is not. The insolubility of the product NaCl pushes the reaction, and replenishing the
NaI would also help.
3. On the first guess I'd think the yield would be the ratio of NaI:NaCl dissolved in acetone if you keep it saturated with NaI and let it go to
equilibrium which should favor the product _but_ you also have the intermediate product of CH2ICl.
2NaI(org) + CH2Cl2(org) <-> NaI(org) + NaCl(?) + CH2ICl(org) <-> 2NaCl(s) + CH2I2(org)
Check the Keq for each step to see if the intermediate production is the faster or slower of the two, and also check to see if NaCl has appreciable
solubility in CH2ICl.
http://www.sciencemadness.org/talk/viewthread.php?tid=12205
[Edited on 31-10-2011 by ldanielrosa]
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Domo_Kun
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Thanks for your answer.
How would I go about figuring out the Keq? You think I can find data on that particular reaction somewhere?
I understand the use of acetone to use the solubility difference and push in one direction.
Will the reaction need heat? And how do I figure out how long I should have the reaction going?
Do I just try it out and see what happens?
Is the boiling point a good enough indicator to indicate that the product is actually DIM? How do I test for or estimate the amount of CH2ICl in the
product?
lots of questions I know, interesting stuff though...
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ldanielrosa
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I don't have answers to all your questions, but I'll do what I can. This has come up before, and I edited my earlier post to include a link.
I don't regularly access the best of the resources, so I can't really help much with the Keq.
I don't know if it is endothermic or exothermic. If you mix some up and there is a significant change in temperature, then you can make some good
guesses: Temperature drop means adding heat may increase the RXN speed. Temperature rise _may_ mean the opposite, but it may also mean it can run
out of control.
I would recommend a freezing point test first. If you can freeze the product at or close to 6°C then it is relatively pure DIM. DCM freezes at
-96°C, and even if it were higher any impurity would depress the freezing point of the majority solvent.
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Domo_Kun
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Thank you for that!
I'll just try something out and post the results here layer 
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