shrent
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Silyl protection with HMDS
Hi friends ! 
I'm trying silyl protection of l-Alanine with Hexamethyldisilazane (HMDS).
i.e. making H2NCH(CH3)COOH to H2NCH(CH3)COOSi(CH3)3.
How can I do this task ? Just mixing & reflux in acetonitrile or something else ? Adding base (TEA) is necessary ?
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shrent
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Making Trimethylsilyl Ester of l-Alanine
I again try to clarify my requirement.
I want to make trimethylsilyl Ester of l-alanine with silylating agents like HMDS, TMCS, BSA (mono silylation at COOH).
I tried stirring alanine with all the above agents separately in diff. solvents (MDC, EDC, EA, CH3CN, etc.) but did not get conversion. 
Can I pls get proper method for this silylation ?
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Nicodem
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Look, you probably haven't noticed it, but this forum is about hobby chemistry. So I don't think any of the members feel the need to do the
Beilstein/SciFinder searches for you. You keep asking the same questions all over again under a couple of nicknames. As a hobby chemist, it is a bit
humiliating to be asked to do work for someone else for free, when this someone is already paid by his company for exactly such work. Don’t you
think so?
OK, I would understand if you would ask for a paper unavailable in your libraries and I would gladly do you a favor. But you are actually asking the
forum members to do the work you are seemingly paid for!
That is damn arrogant if you ask me.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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shrent
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Nicodem versus Shrent
Dear Nicodem,
I simply disagree with you & the views you posted. What is wrong with you, dear ?
First, for your kind information, I'm not being paid by any company & doing my own research for my own r&d laboratory. It is right that from
these r&d I'm earning something by getting ideas & views from the chemists around the globe for my work. But what is wrong with it ? Because
ultimately it is a simple exchange of knowledge from an experienced person to an unexperienced buddy.
I'm sure there are so many members on this board who are having background like me & are pleased to exchange their knowledge without any
hesitations. Even I'm always willing to help someone with my experience & upon this help, if he gets some rewards or money than what is wrong in
it ?
I kindly request most of the members of this forum to pls give views on this discussion (not on my original query but between me & Nicodem !). So
that, ultimately, if I'm wrong from my side, I will simply rub-out my name from this forum.
Awaiting your replies............
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chemoleo
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Could you please cite some papers/publications where it states that this reaction is supposed to work in the first place?? What is the reaction
mechanism? You realise that the COOH exists as COO-, so this may prevent the reaction, depending on the mechanism.
| Quote: | | i.e. making H2NCH(CH3)COOH to H2NCH(CH3)COOSi(CH3)3. |
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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mick
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Try blocking/protecting the NH groups first and then activating the COOH by forming an amide,amidite or imidate.
mick
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shrent
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| Quote: | Originally posted by chemoleo
Could you please cite some papers/publications where it states that this reaction is supposed to work in the first place?? What is the reaction
mechanism? You realise that the COOH exists as COO-, so this may prevent the reaction, depending on the mechanism.
| Quote: | | i.e. making H2NCH(CH3)COOH to H2NCH(CH3)COOSi(CH3)3. |
Dear chemoleo,
I had attached one file I have, if it is of interest to you. Take a look at that.
[Edited on 24-6-2006 by shrent]
Attachment: E019936073.pdf (215kB)
This file has been downloaded 2043 times
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shrent
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Removing HCl
Hey friends !
I got a very nice process for this. I just mixed TMCS (1.1 eq.) with L-Alanine in DMF at room temperature & after 10-15 minutes stirring, all
alanine got dissolved.
But the problem here I face is the HCl liberated during the reaction. For this, I added TEA (1 eq. against TMCS) in the reaction but besides making
the TEAHCl, it also affects the TMS ester generating insoluble particles.
Can you pls suggest me how to overcome this HCl & making the reaction media neutral without using TEA ?
By the way, here I assume that the TMS-L-Alanine is liquid ????? Do you have exact idea about that if it is liquid or solid ? (Sorry, I tried first
time for this material & could not get any information about its nature from net......)
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stoichiometric_steve
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| Quote: | Originally posted by shrent
Can you pls suggest me how to overcome this HCl & making the reaction media neutral without using TEA ? |
bwahahaha...sodium carbonate.
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shrent
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Na2CO3 !!!!!
No dear, It is not possible to use Na2CO3. Becoz it will generate water upon neutralization & consequently it will immediately hydrolyze my
silylester.....!!!
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chemoleo
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Question- have you ascertained that TEAHCl is soluble in the solvents you use? Maybe it is simply precipitated TEA salt... and not your 'affected'
trisilyl ester.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Nicodem
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Na2CO3 + HCl --> NaHCO3 + HCl
Where do you see any water formation in the reaction of Na2CO3 with HCl?
Only if you used too little Na2CO3, could H2O be formed by further neutralization of NaHCO3. Furthermore, Na2CO3 is a drying agent!
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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shrent
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Pls balance
| Quote: | Originally posted by Nicodem
Na2CO3 + HCl --> NaHCO3 + HCl
Where do you see any water formation in the reaction of Na2CO3 with HCl? |
Oh dear !
I will be so happy, if you can you pls balance your reaction..! I am very much
surprised that you can make NaHCO3 from simply the Nacarbonate & HCl....!!!! 
I hope, it should be :
Na2CO3 + 2HCl --------> 2NaCl + H2O + CO2
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Nicodem
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You got me there.
It should be:
Na2CO3 + HCl --> NaHCO3 + NaCl
No water forms, as you can see. It is simply because the pKa1 and pKa2 of "carbonic acid" are far apart (in water they are 6.3 and 10.3; hence a
10,000 difference in basicity!).
Your equation can not happen, unless you use only half equivalent of Na2CO3. Anyway, if you are an organic chemist you should be familiar of the
common use of sodium and potassium carbonate as weak bases where anhydrous conditions are preferred. Obviously, K2CO3 is way preferred due to its much
higher solubility in organic solvents (acetone, acetonitrile, alcohols...) and higher basicity in them. Therefore, I see absolutely no point in
discussing on such a common method that’s used already for more than a century.
I still think you should do your own literature search before asking others to them for you. You keep on posting these questions on several chemistry
forums all over the net under several nicknames. You even use different nicknames on this same forum. Why do you do that? Can’t you go to the
library like every normal chemist and do the job you are supposed to do by yourself? Then, if you stumble in some problem you are unable to solve with
your own effort, you can still ask other chemists. But you are doing this in reverse which is highly annoying to me.
PS: And stop dear-ing me! I find it humiliating. I’m not your “dear”!
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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shrent
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Just stop this......
Nicodem,
You're right that I'm posting my questions with other online forums also, BUT NOT WITH ANY OTHER NICKNAMES.......
YOU GOT IT ?
You're also not at all to be called a "DEAR" from any sort, that I also fully agree with you...!!
I request you to pls just don't post your comments onto my posting & just discard it from your views. I'm sure, I will be getting enough replies
for my queries from other friends.
Goodbye......
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enhzflep
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| Quote: | Originally posted by shrent
Dear Nicodem,
First, for your kind information, I'm not being paid by any company & doing my own research for my own r&d laboratory. It is right that from
these r&d I'm earning something by getting ideas & views from the chemists around the globe for my work.
I kindly request most of the members of this forum to pls give views on this discussion (not on my original query but between me & Nicodem !). So
that, ultimately, if I'm wrong from my side, I will simply rub-out my name from this forum.
Awaiting your replies............ |
Well, Shrent.
Where to start? Where to start?
I am personally curious as to what the development is needed for if not the production of an income.
Pretty much everybody here performs R but the &D? Perhaps one of the manifestations of your struggle over the language barrier.
While understanding that if your intentions are pure and you are in fact engaged in some other activity for the procurement of a wage, that you would
feel somewhat riled by some of the comments directed at yourself, I must say that it does seem rather amusing that somebody with your slippery grip on
the English language has decided to use condecention against an established member such as Nicodem.
If you were to improve the grammar, punctuation and spelling of your posts, so as they were not all over the shop like a drunk on Friday night - if
you were to do this and respect the etiquete displayed (for the most part) on this board, then you would find it somewhat easier to obtain the
information that you seek.
UNDERSTAND?? Bloody.
[Edited on 5-7-2006 by enhzflep]
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shrent
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Okay........
Okay.
Thanks for your support friends.......
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