Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Zainb on November 22, 2011, 04:11:54 AM
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Any help is welcome to explain:
Mechanism of deprotection of TMS-alkynyl compound by K2CO3
TMS–C≡C-R + K2CO3 :rarrow: H–C≡C-R
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Any help is welcome to explain:
Mechanism of deprotection of TMS-alkynyl compound by K2CO3
TMS–C≡C-R + K2CO3 :rarrow: H–C≡C-R
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I take it that this is aqueous pot carb?
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Silicon loves oxygen almost as much as it loves fluorine.
EDIT: Si can also go pentavalent if attacked by oxygen or fluorine.
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Silicon loves oxygen almost as much as it loves fluorine.
EDIT: Si can also go pentavalent if attacked by oxygen or fluorine.
But there must be a proton source in this example.
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Excellent point. I was assuming it was aqueous (or water-THF/MeOH/ACN/whatever).
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The used solvent is methanol which firstly reacted with K2CO3 to give potassium methoxide CH3O-K+
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The used solvent is methanol which firstly reacted with K2CO3 to give potassium methoxide CH3O-K+
Really? From the pKas, that looks to me to be about five orders of magnitude in the wrong direction. Do you think there would be any significant concentration of methoxide in this solution?
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http://pubs.acs.org/doi/abs/10.1021/je020012v
in this paper, there are more explanation on the solubility of potassium carbonate in the methanol.
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http://pubs.acs.org/doi/abs/10.1021/je020012v
in this paper, there are more explanation on the solubility of potassium carbonate in the methanol.
In that case the mechanism of de-silylation becomes obvious. In fact it should be catalytic in base.
Do you have any ideas?
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In that case the mechanism of de-silylation becomes obvious. In fact it should be catalytic in base.
Do you have any ideas?
TMS-acetylenes can removed under basic conditions
K2CO3 + 2MeOH ::equil:: 2K+-OMe + H2O + CO2
-OMe will attack Si to give pentavalent coordination intermediate..
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In that case the mechanism of de-silylation becomes obvious. In fact it should be catalytic in base.
Do you have any ideas?
TMS-acetylenes can removed under basic conditions
K2CO3 + 2MeOH ::equil:: 2K+-OMe + H2O + CO2
-OMe will attack Si to give pentavalent coordination intermediate..
And the proton originates from the methanol regenerating methoxide which is what I meant about being catalytic in base.
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Still not clear if the triple bond will contribute in the breaking of the bond (with red colour) Si–C≡C in the structure TMS–C≡C-R.
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Still not clear if the triple bond will contribute in the breaking of the bond (with red colour) Si–C≡C in the structure TMS–C≡C-R.
No contribution from the triple bond.
The nucleophile attacks the Si atom and the electrons from the C-Si bond pick up a proton from the solvent, which is why I said it is catalytic in base.
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The solvent is MeOH...
Thanks a lot discodermolide.
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Hello
You can show a complete mechanism of this reaction please.
Thanks