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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Hachiko on December 11, 2019, 11:42:14 PM
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I synthesize the stannane compound using n-BuLi and Bu3SnCl with aryl halide. I do the experiment and monitor by TLC. Firstly I add n-BuLi,I see that after Lithiation, all starting material changes (new spot appears) so I add Bu3SnCl, but there is no new spot appears(TLC seems not to change when compare with the one when I finish lithiation).
So I wonder that will the TLC change a lot from lithiation (when Li attached) to final product (when Tin attached). Could anyone share your experience?
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If you do lithio-halogen exchange with BuLi you can se a change after lithiation, if you use BuLi to pick a proton you see no change on TLC. The Bu3Sn is very lipophilic and iften you see thespots comming higher when you get stannane.
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If you do lithio-halogen exchange with BuLi you can se a change after lithiation, if you use BuLi to pick a proton you see no change on TLC. The Bu3Sn is very lipophilic and iften you see thespots comming higher when you get stannane.
So if I get the stannane, the spot of product will go higher than the spot I get when I finish lithiation process?
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You must understand that the lithiated molecule will be hydrolysed when put on a TLC-plate. If you show your structure I can help you.
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You must understand that the lithiated molecule will be hydrolysed when put on a TLC-plate. If you show your structure I can help you.
Thank you for your information. I really don't know that before. I synthesize tributyl(5-octylthiophen-2-yl)stannane from 2-bromo-5-octylthiophene. Could you share your experience?
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Then you should se a change in RF when you lithiate because the bromo will be changed to hydrogen. I am surpised that this chemistry does not work, is there a possibility that the stannane has same Rf as the hydrogen-compound?
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Then you should se a change in RF when you lithiate because the bromo will be changed to hydrogen. I am surpised that this chemistry does not work, is there a possibility that the stannane has same Rf as the hydrogen-compound?
Yes, I see a change in TLC when I add n-BuLi, but when I add Bu3SnCL there is no change from that. I check for NMR but the structure is matched to octylthiophene. I see this kind of reaction is really straightforward with the high reaction yield, but in my case, it isn't.
Is it about the problem from Bu3SnCl reactivity?
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I have never worked with tin, so I am not sure how stable Bu3SnCl is, but is it possible that you have a bad reagent?
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The reaction can be slow, how long time do you run? I agree that the reagent can be bad if its an old bottle.
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You must understand that the lithiated molecule will be hydrolysed when put on a TLC-plate. If you show your structure I can help you.
Thank you for your information. I really don't know that before. I synthesize tributyl(5-octylthiophen-2-yl)stannane from 2-bromo-5-octylthiophene. Could you share your experience?
you should take a sample and quench it before you do the TLC the spot wou see will correspond to 5-octylthiophene. if you are having trouble with tlc then a crude NMR of a small sample of reaction mixture might help.
how are you visualizing the TLC?
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One good way to quench this time of sample is to mix it with a dropp of acetone, RF should go down if the lithiation is successfull.
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I have never worked with tin, so I am not sure how stable Bu3SnCl is, but is it possible that you have a bad reagent?
I bought it from Sigma but I have opened for several months.
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The reaction can be slow, how long time do you run? I agree that the reagent can be bad if its an old bottle.
I added BuLi and waited till all starting material change into low Rf. Adding Bu3SnCl, keep at -78oC for 1 hour and increase to room temperature for 24hrs.
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you should take a sample and quench it before you do the TLC the spot wou see will correspond to 5-octylthiophene. if you are having trouble with tlc then a crude NMR of a small sample of reaction mixture might help.
how are you visualizing the TLC?
[/quote] You mean after quenching, the spot I see will be 5-octylthiophene. I visualize TLC under UV light.
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One good way to quench this time of sample is to mix it with a dropp of acetone, RF should go down if the lithiation is successfull.
after quenching with acetone, will I see the spot of R-Li? If I don't quench, which kind of spot will I see? Because in this case, after lithiation I see a new spot with lower Rf to compare with starting material (5-octylthiophene)
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One good way to quench this time of sample is to mix it with a dropp of acetone, RF should go down if the lithiation is successfull.
after quenching with acetone, will I see the spot of R-Li? If I don't quench, which kind of spot will I see? Because in this case, after lithiation I see a new spot with lower Rf to compare with starting material (5-octylthiophene)
If you quench with acetone, you get the tertiary alcohol from addition to the carbonyl in acetone, this product will be much more polar then the starting material. If you dont quench you will see the compound with a hydrogen instead of a bromo because the lithio-compound will be hydrolyzed on contact with moisture and silica on the tlc-plate. This compound will also be a little more polar then the startingmaterial.
I think you are doing everything right, its surprising it does not work.
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One good way to quench this time of sample is to mix it with a dropp of acetone, RF should go down if the lithiation is successfull.
after quenching with acetone, will I see the spot of R-Li? If I don't quench, which kind of spot will I see? Because in this case, after lithiation I see a new spot with lower Rf to compare with starting material (5-octylthiophene)
If you quench with acetone, you get the tertiary alcohol from addition to the carbonyl in acetone, this product will be much more polar then the starting material. If you dont quench you will see the compound with a hydrogen instead of a bromo because the lithio-compound will be hydrolyzed on contact with moisture and silica on the tlc-plate. This compound will also be a little more polar then the startingmaterial.
I think you are doing everything right, its surprising it does not work.
Thank you for your sharing.
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Are there any methods for me to treat Bu3SnCl to reuse it?
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Do you mean purify it? Distillation.
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Do you mean purify it? Distillation.
Thank you!
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Do you mean purify it? Distillation.
Distillation seems a little bit dangerous because it's toxic. Could I use the molecular sieve to remove water inside? Because I think the problem may come from the moisture.
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No, if you get moisture it will react very fast, you get the tributyltinoxide.
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No, if you get moisture it will react very fast, you get the tributyltinoxide.
You means moisture will react with Bu3SnCl to form tributyltinoxide. So could it be the reason why Bu3SnCl doesn't work? I doubt that problem come from Bu3SnCl.
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I would check the purity of the stannane, NMR works fine for it. If your bottle is old, get a new one its not that expensive.
Im not sure exactly about your procedure but I would use different base because BuLi can react with tributyltinCl to form tetrabutyl tin. Try LDA or tBuLi.
Quench the organoLi with water before TLC to get the dehalogenated aryl (if you have TLC of that) you can also use DMF to get the aldehyde and stain it with DMP.
Also, the reaction might need some time and temperature, maybe warm it to room temperature after the addition is complete. The organotin reagents are super nonpolar, be sure to check with suitable mobile phases (we used pure hexanes for that).
Maybe check this procedure
http://orgsyn.org/demo.aspx?prep=CV8P0268
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I would check the purity of the stannane, NMR works fine for it. If your bottle is old, get a new one its not that expensive.
Im not sure exactly about your procedure but I would use different base because BuLi can react with tributyltinCl to form tetrabutyl tin. Try LDA or tBuLi.
Quench the organoLi with water before TLC to get the dehalogenated aryl (if you have TLC of that) you can also use DMF to get the aldehyde and stain it with DMP.
Also, the reaction might need some time and temperature, maybe warm it to room temperature after the addition is complete. The organotin reagents are super nonpolar, be sure to check with suitable mobile phases (we used pure hexanes for that).
You can not use LDA if you want metal-halogen excange as in this case. N-BuLi works fine is my experience. You will get quench automaticaly if you put the lithiated material on a TLC-plate.
Maybe check this procedure
http://orgsyn.org/demo.aspx?prep=CV8P0268
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Yeah youre right, LDA doesnt exchange, I mixed that up with procedure we used (Bu3SnH + LDA then quench with electrophile)
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Yea kriggy, thats an interesting reagent, Bu3SnLi, I have used it too. Its a "lithiated metal".
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Thank you all for your valuable advice.
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I have already known my problem for a time but I'm so busy. Now I think that someone may need to know the reason. The reason I'm failed with reaction is that I don't use 2 equiv of n-BuLi.
For lithium halogen exchange, to be certain you should use 2 equivalents of t-BuLi at -78 degrees, generally takes about an hour.
The first equivalent undergoes Li-halogen exchange and the second equivalent of t-BuLi causes E2 elimination of the t-BuBr side product to produce unreactive isobutylene. If you don't use two equivalents the desired thiophenyllithium may cause the E2 elimination giving you thiophene.
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Do you use t-BuLi or n-BuLi? n-BuLi does not give elimination. With t-BuLi its important sometimes to use 2equi. like you say.
If you do lithium-halogen exchange with n-BuLi you get n-BuBr and this can react with you lithio-thiophene but generally the tin chloride reacts faster.
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I used n-BuLi but base on my experience, 2 equiv n-BuLi is necessary for reaction. I changed from 1.2 equiv to 2 equiv and saw a huge difference.
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This could be explained by presence of protic material in you reaction solution, such as water, also oxygen or carbon dioxide would consume BuLi.
n-BuLi does not react with n-BuBr, att least not att any significant speed.
Its nice that you got it working!
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Thank you. Protic source may be also a possibility as you mentioned.