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Author: Subject: Methyl iodide purification
DoctorOfPhilosophy
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[*] posted on 30-5-2016 at 16:25
Methyl iodide purification


Just prepared some methyl iodide using the "aluminum foil" method (https://www.youtube.com/watch?v=8zzQVLr1ddo). Any idea if I can purify with sodium bicarbonate? I added a little and it reacts, but I don't know if it's destroying the MeI. Also Wikipedia says sodium thiosulfate but I don't have it on hand.

MeI(3).png - 262kB
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BromicAcid
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[*] posted on 30-5-2016 at 19:08


Old school would be to shake it with mercury. But what are you trying to purify from? Do you have yellow/brown coloration? Trying to get rid of water? Trying to get rid of MeOH? Trying to increase the purity in general?



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UC235
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[*] posted on 30-5-2016 at 19:35


Methyl iodide doesn't react with bicarbonate solution at any reasonable pace. If it fizzes, you have some HI present from decomposition/solvolysis.

Saturated bicarb (add a tiny bit of sulfite or bisulfite to remove iodine traces) will remove HI and methanol (to an extent)
Concentrated sulfuric acid will remove anything that isn't MeI (but watch out for heating if it's very wet or contains MeOH)

MeI is best stored in a freezer in the dark over copper powder.
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chemplayer...
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[*] posted on 31-5-2016 at 05:04


Washing with a little dilute sodium hydrogen sulfite or sodium thiosulfate solution will remove any yellow/brown iodine. If the product is still coloured after this then you've got some unusual impurity present. Separate off the dense bottom liquid and then re-distill it to get pure methyl iodide. Keep this in a very well sealed bottle (as UC235 says in the freezer is a good idea) and with a few granules of anhydrous CaCl2 to keep it dry. Then it's pretty much Grignard ready out of the bottle.

If the product after washing is pure water coloured and you don't mind accepting a slightly lower quality of product, you can then separate and dry at this stage without re-distilling. If you want to use for a Grignard reaction then best to re-distill though. Depends what your ultimate aim is...




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DoctorOfPhilosophy
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[*] posted on 1-6-2016 at 19:09


Thanks everyone for your help. That explains why I couldn't get the colour out with bicarb. I'll try thiosulfate, I found some from an old chemistry set. the colour probably is the iodine.
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