Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: baum0372 on July 08, 2014, 11:27:19 PM
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I am trying to use 8 ul of trimethylsilyl iodide to perform a deprotection of a benzyl ester on a small scale 15mg, then heating to 40C overnight in DCM.
I am wondering how you all would set up the reaction, including reaction vessel, how you would ensure water is removed. I know I can always use xs reagent, but I am wondering what else one can do.
Currently my set up is in a 25mL schlenk tube (smallest we have). I did my best to add 8ul by hamilton syringe but I feel a lot of it didn't quite make it down the schlenk tube, plus some white smoke was noticed, so I'm sure that all 8ul didn't get in.
Also, trimethylsilyl iodide is shipped in a 25mL ampoule. I just broke it and quickly transferred to a schlenk tube, the color is now a pale yellow, rather than clear. Was this the proper way to store it?
Any advice in general on working with air sensitive reactions on small scale would be appreciated. Thanks!
Ryan
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1) Make the trimethylsilyl iodide in solution. I suggest using hydrophobic solvent like hexane, benzene, toluene. This gives much larger volume to ease accurate measurement of the amount you add to the system
2) The pale yellow color might be iodine which might be resulted from hydrolysis and subsequent oxidation of I-.
3) The initial transfer of the sample may be done in glove box. But glove box does not welcome liquids.
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I did not have access to state-of-the-art organic laboratory equipment, and I am not a card-carrying organic chemist. Bearing those things in mind, I can still say that I found TMSI very difficult to handle. It tended to decompose very rapidly in my hands. I ended up essentially making it in situ. Is this a carboxylic ester or a phosphoric ester? If it is the latter, I think that TMSBr might be an easier reagent to use.
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Hi Babcock and kamiyu, thanks for the reply.
It's good to know the TMSI is difficult to handle because that is certainly how I found it. I may end up making a stock solution in an organic solvent using the glovebox, then using a mini-inert valve to keep the solution sealed off to the air. Then I should be able to use a regular syringe to measure out the reagent at regular intervals.
I am reducing a carboxylic ester so I will likely need to use the TMSI instead of TMSBr.
It looks like one can use hexamethyldisilane + I2 to make the TMSI in situ, but is the hexamethyldisilane just as difficult to handle?
Thanks guys.
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Hexamethyldisilane is a sterically hindered secondary amine. Should be fine.
Is the preparation of TMSI from iodine and hexamethyldisilane previously reported??
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The synthesis of TMSI is previously reported, however they use hexamethyldisilane which does not contain an amine, it's just a dimer of TMS. From my searching it looks like this is more reasonably stable.
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I used TMS-O-trifluoromethanesulfonate and tetrabutylammonium iodide.
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I think this is typical SN2 reaction. DMSO, rt, excess TBAI right?
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The reaction I am thinking of was the removal of methylester protecting groups from a derivative of phosphoric acid. The reaction conditions were in DCM around -30 °C if I recall correctly.