Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: linh_ngt on November 09, 2012, 11:42:47 AM
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Dear all member,
As I know, imine could be easily formed by reaction of aldehyde and amine, but when i carry out this reaction, it doesnt work and I'm really confused.
My reaction conditions: starting materials (1eq), amine (1.5 eq), MgSO4 (4eq), dry Ch2Cl2 mixed together and kept at 30 -40oC, put overnight but when I check on TLC, there's still starting material left. Even when I try to treat the reaction (just to obtain the product), purify by CC, I can not have desire product. Dont know why because this's a simple reaction??
And I also try this reaction using microwave, but no effective :-<
Is there any helpful opinion? I'm quite confused. And actually, i used directly starting material (aldehyde) from previous reaction, without treatment ( using oxalyl chloride, DMSO, dry CH2Cl2)
Thank you a lot for your comments!
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There is water formed in this reaction, you need to remove it. Add anhydrous magnesium sulphate to your DCM solution, and stir.
Imines are probably not stable to TLC, so be careful when interpreting tlc results. Same goes for CC. Use NMR to judge if the reaction is complete. Don't isolate it, remove the solvent and use it directly. I have a few methods for making various imines of amino acids with aldehydes.
Try this: (Note aden of Et3N is to generate the free amino group so it can react.
A suspension of the gylcine ester hydrochloride salt (other salts can also be used, for example tosylate salts) (1 equivalent) was stirred in methylene chloride for ten minutes and treated with 10 equivalents of anhydrous magnesium sulphate, and stirring continued for 1 hour at room temperature. A solution of the aldehyde (1 equivalent) in methylene chloride was added within 5 minutes at room temperature followed by dropwise addition of triethylamine or a similar tertiary organic base (2 equivalents). Stirring was continued for 20 hours at room temperature, and the mixture was filtered. The solvent was removed in vacuum to give an oily solid. Tert-Butyl-methyl ether was added slowly while stirring to crystallise the triethylamine hydrochloride, which was removed by filtration after stirring the mixture for 1 hour at room temperature. The solvent was then removed from the filtrate to give the desired imine as an oil, or in some cases a solid which were used without further purification.
Yields very very high >98%.
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There is water formed in this reaction, you need to remove it. Add anhydrous magnesium sulphate to your DCM solution, and stir.
Imines are probably not stable to TLC, so be careful when interpreting tlc results. Same goes for CC. Use NMR to judge if the reaction is complete. Don't isolate it, remove the solvent and use it directly. I have a few methods for making various imines of amino acids with aldehydes. I can post one if you wish.
Yes, I use anhydrous MgSO4 and dry CH2Cl2 already and I think that'll be effective to remove water. Even when I treat the reaction, I mean that I just filtrate to remove MgSO4, evaporate to remove CH2Cl2 then check it on NMR, but still can not observe the desire product :-<
Of course I thank you a lot for your post, also your comment about my reaction :)
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The hit it harder. Use toluene and Dean-Stark out the water formed. I assume you can do this on a reasonable scale?
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The hit it harder. Use toluene and Dean-Stark out the water formed. I assume you can do this on a reasonable scale?
I also think about this way. But I just wanna try with small amount of aldehyde, so I think Dean-stark's not suitable for this case?
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The aldehyde must be readily available? If so you can do a larger reaction.
If not try anhydrous copper sulphate.
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You may need to increase temperature. This usually makes drying agents less effective, so you might need to switch to molecular sieves, or if your temperature is high enough, to drying tubes or Dean-Stark traps.
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I can imagine a lot that can occur in this reaction, what are you finding? The description is as though it is no reaction. Is that really true or are you seeing different products than expected?
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when I check on TLC, there's still starting material left. Even when I try to treat the reaction (just to obtain the product), purify by CC, I can not have desire product. Dont know why because this's a simple reaction??
I can't see your picture, but I also suspect the problem is that your imine is unstable on silica, and decomposes back to the starting materials as soon as you spot it on a TLC plate or load it onto a silica column:
Imines are probably not stable to TLC, so be careful when interpreting tlc results. Same goes for CC. Use NMR to judge if the reaction is complete. Don't isolate it, remove the solvent and use it directly.
The reaction may be working perfectly well, you are just using an inappropriate technique for monitoring/purification. What does the crude NMR look like?
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Thank everyone,
actually, i just increase temp to nearly 50oC, under argon conditions and MgSO4.
As u say, maybe when i check reaction on TLC, imine could be changed into starting material. I conclude that because when I test the crude product on NMR, I dont see the starting material left but there's also no desire product (my treatment: filtration for removing MgSO4 and evaporate for removing CH2Cl2, then check by NMR).
Here I attach my reaction file. Thank u a lot for your comments!
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when I test the crude product on NMR, I dont see the starting material left but there's also no desire product
Just to make absolutely sure, you should treat your CDCl3 with anhydrous K2CO3. There can be enough HCl in chloroform to catalyse the decomposition of some imines - I have personally experienced this problem and wasted a significant amount of time because I thought my reactions were not working when in fact they were working perfectly.
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Well, i used dry CH2Cl2 for treatment process.
Here I show you the NMR data of the crude product (without purification).
Could you give some comments for that?
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I do not see the data!
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oops, I attach the data again ( jpg file)
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That NMR looks very strange, not much imine I think.
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I think it has my desire product already. This is just the crude product but I'll not purify this crude, just use for next reaction.
Do you think it's ok?
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I don't think there is much imine in there.
I would start again. Use the method Dan suggested for purifying the chloroform.
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In this reaction, i use dichloromethane, not chloroform.
In NMR data, I observe some peaks of desire product: aromatic protons of phenyl group, proton of CH=N- bond, 4H of -O-CH2-CH2-O-, 2CH3 and there is no starting material left ( no more peak of CH of aldehyde group, for sure).
I'll try to make this reaction again using CHCl3 solvent dried by K2CO3; and also I'll try the next reaction without purification
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As far as I could see there were 24 aromatic protons in this spectrum, but it was difficult to see the number.
24 aromatic protons don't fit with the structure.
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I think 24 aromatic protons would be include aromatic protons of amine left ( I used 1.5 eq amine compared with 1 eq aldehyde)
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I posted a method for you give that a try?
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There is water formed in this reaction, you need to remove it. Add anhydrous magnesium sulphate to your DCM solution, and stir.
Imines are probably not stable to TLC, so be careful when interpreting tlc results. Same goes for CC. Use NMR to judge if the reaction is complete. Don't isolate it, remove the solvent and use it directly. I have a few methods for making various imines of amino acids with aldehydes.
Try this: (Note aden of Et3N is to generate the free amino group so it can react.
A suspension of the gylcine ester hydrochloride salt (other salts can also be used, for example tosylate salts) (1 equivalent) was stirred in methylene chloride for ten minutes and treated with 10 equivalents of anhydrous magnesium sulphate, and stirring continued for 1 hour at room temperature. A solution of the aldehyde (1 equivalent) in methylene chloride was added within 5 minutes at room temperature followed by dropwise addition of triethylamine or a similar tertiary organic base (2 equivalents). Stirring was continued for 20 hours at room temperature, and the mixture was filtered. The solvent was removed in vacuum to give an oily solid. Tert-Butyl-methyl ether was added slowly while stirring to crystallise the triethylamine hydrochloride, which was removed by filtration after stirring the mixture for 1 hour at room temperature. The solvent was then removed from the filtrate to give the desired imine as an oil, or in some cases a solid which were used without further purification.
Yields very very high >98%.
U mean this method??? WHen can I put my amine (1-phenyl ethylamine) because I dont see this information and I also dont have this kind of salts
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Tell us what you are trying to do. I suspect you are trying way to hard and you can make your desired product a lot more easily, but I could be wrong because I don't know what you are trying to make.
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Tell us what you are trying to do. I suspect you are trying way to hard and you can make your desired product a lot more easily, but I could be wrong because I don't know what you are trying to make.
I just wanna synthesize this imine from this aldehyde
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Look, instead of the glycine ester substitute your amine, and leave out the triethylamine. Everything else the same.
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Leaving out of triethyl amine means that I did this method already, just change the amount of MgSO4 (10 eq--> 5eq) :)
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I just wanna synthesize this imine from this aldehyde
… This is just the crude product but I'll not purify this crude, just use for next reaction.
Next reaction? Why not just react 4-methoxybut-3-en-2-one with your amine? Wait, we still don't know what you are trying to do in the next reaction. Even as naive as I may appear, the dioxolane looks suspiciously like a protecting group. If so, there must be a next reaction. If that were true, perhaps you could take a chance that not only could we suggest how to make the imine, but we could actually suggest how to get to the product of the next reaction.
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I just wanna synthesize this imine from this aldehyde
… This is just the crude product but I'll not purify this crude, just use for next reaction.
Next reaction? Why not just react 4-methoxybut-3-en-2-one with your amine? Wait, we still don't know what you are trying to do in the next reaction. Even as naive as I may appear, the dioxolane looks suspiciously like a protecting group. If so, there must be a next reaction. If that were true, perhaps you could take a chance that not only could we suggest how to make the imine, but we could actually suggest how to get to the product of the next reaction.
Next reaction that I want to make is the reaction of Danishefsky's diene with imine to obtain the follwing compound ( attached file). Exactly the dioxolane is a protecting group :)Could you kindly give me some clues?
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That makes it a horse of a different color. Is the imine of alpha-methylbenzylamine or benzylamine and butyraldehyde a known compound? I would check to see how they were made.
I don't have experience with imines of the type you are trying to prepare. I know that if one wishes to prepare an enamine of an aldehyde, what forms is the aminal with potassium carbonate. This is cracked to get the enamine. Although it seemed better that you had a dioxolane, but I don't necessarily think it survived the imine forming reaction. This looked different than what I thought the spectrum should look like, but I really don't know. I don't know what the starting materials looked like. It could be okay, but aldehydes are pretty easily enolized, etc. I could imagine competing reactions occurring here.
I cannot advise you on this particular reaction, but you should be able to find reaction conditions for more simple analogs to find optimal conditions. Given the difficulties you are incurring, the complexity of the reaction you wish to try, I would hone my technique by synthesizing a simpler intermediate first. We've all faced your question, "Is it me, or is it the reaction?" We can't answer that. You need to establish that yourself. Your conditions were plausible enough. Do they work with enolizable aldehydes? with beta-alkoxy aldehydes?