July 07, 2020, 02:44:21 PM
Forum Rules: Read This Before Posting


Topic: Mechanism of deprotection of TMS-alkynyl compound by K2CO3  (Read 31952 times)

0 Members and 1 Guest are viewing this topic.

Offline Zainb

  • Regular Member
  • ***
  • Posts: 29
  • Mole Snacks: +0/-0
Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« on: November 22, 2011, 04:11:54 AM »
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
~~~~~

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +404/-70
  • Gender: Male
    • My research history
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #1 on: November 22, 2011, 05:35:40 AM »
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
~~~~~

I take it that this is aqueous pot carb?
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Honclbrif

  • Chemist
  • Full Member
  • *
  • Posts: 659
  • Mole Snacks: +58/-10
  • Gender: Male
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #2 on: November 22, 2011, 09:22:34 AM »
Silicon loves oxygen almost as much as it loves fluorine.

EDIT: Si can also go pentavalent if attacked by oxygen or fluorine.
Individual results may vary

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +404/-70
  • Gender: Male
    • My research history
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #3 on: November 22, 2011, 10:25:28 AM »
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.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Honclbrif

  • Chemist
  • Full Member
  • *
  • Posts: 659
  • Mole Snacks: +58/-10
  • Gender: Male
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #4 on: November 22, 2011, 10:40:34 AM »
Excellent point. I was assuming it was aqueous (or water-THF/MeOH/ACN/whatever).
Individual results may vary

Offline Zainb

  • Regular Member
  • ***
  • Posts: 29
  • Mole Snacks: +0/-0
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #5 on: November 22, 2011, 12:45:20 PM »
The used solvent is methanol which firstly reacted with K2CO3 to give potassium methoxide CH3O-K+

Offline fledarmus

  • Chemist
  • Sr. Member
  • *
  • Posts: 1676
  • Mole Snacks: +203/-28
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #6 on: November 22, 2011, 02:35:05 PM »
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?

Offline Zainb

  • Regular Member
  • ***
  • Posts: 29
  • Mole Snacks: +0/-0
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #7 on: November 22, 2011, 03:07:38 PM »
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.

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +404/-70
  • Gender: Male
    • My research history
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #8 on: November 22, 2011, 03:12:54 PM »
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?
« Last Edit: November 22, 2011, 03:59:07 PM by discodermolide »
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Zainb

  • Regular Member
  • ***
  • Posts: 29
  • Mole Snacks: +0/-0
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #9 on: November 24, 2011, 03:08:52 AM »

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..


Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +404/-70
  • Gender: Male
    • My research history
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #10 on: November 24, 2011, 05:37:47 AM »

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.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Zainb

  • Regular Member
  • ***
  • Posts: 29
  • Mole Snacks: +0/-0
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #11 on: January 31, 2012, 10:08:20 AM »
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.

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +404/-70
  • Gender: Male
    • My research history
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #12 on: January 31, 2012, 10:38:05 AM »
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.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Zainb

  • Regular Member
  • ***
  • Posts: 29
  • Mole Snacks: +0/-0
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #13 on: February 02, 2012, 05:00:36 AM »
The solvent is MeOH...

Thanks a lot discodermolide.

Offline nelson correia

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
Re: Mechanism of deprotection of TMS-alkynyl compound by K2CO3
« Reply #14 on: May 05, 2016, 07:24:52 AM »
Hello

You can show a complete mechanism of this reaction please.
Thanks

Sponsored Links