Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: manhnhan510 on February 10, 2012, 12:28:15 PM
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Help me!
I measured 0.21g (2mmol) benzaldehyde (liquid), 0.25g (2mmol) anilin (liquid), 0.3g Montmorillonte K-10. Then, the mixture was placed in a flask and mechanically stirred for 1h at room temperature conditions. Next, i added Cloroform (15mL) to the mixture, filtered it off, with vaporization of the filtrate. Accord theory, i should get the solid product, but i didn't. Why??? Plz help me!
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Did you perchance get a liquid product, or no product at all?
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Help me!
I measured 0.21g (2mmol) benzaldehyde (liquid), 0.25g (2mmol) anilin (liquid), 0.3g Montmorillonte K-10. Then, the mixture was placed in a flask and mechanically stirred for 1h at room temperature conditions. Next, i added Cloroform (15mL) to the mixture, filtered it off, with vaporization of the filtrate. Accord theory, i should get the solid product, but i didn't. Why??? Plz help me!
This would suggest that the reaction did not take place. Try leaving it longer, overnight?
Aniline is not the best base for this.
Try a different agent to remove the water, anhydrous copper sulfate is a good one.
Use dichloromethane instead of chloroform. the latter is too toxic.
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What did your TLC show you? (Was your benzaldehyde and aniline fresh?)
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Did you perchance get a liquid product, or no product at all?
yes, i got a liquid product, lightyellow liquid, but no any crystal
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Did you perchance get a liquid product, or no product at all?
yes, i got a liquid product, lightyellow liquid, but no any crystal
What does an NMR indicate or a HPLC? Or even an IR.
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Did you perchance get a liquid product, or no product at all?
yes, i got a liquid product, lightyellow liquid, but no any crystal
What does an NMR indicate or a HPLC? Or even an IR.
OMG, the price for every running NMR or HPLC is very high :(. I'm in Viet Nam, you know. According a theory, the reaction between anilin & benzaldehyde with Montmorillonite K-10 are take place in 10mns at room temperature. But i don't know why i can't do that.
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Did you perchance get a liquid product, or no product at all?
yes, i got a liquid product, lightyellow liquid, but no any crystal
What does an NMR indicate or a HPLC? Or even an IR.
OMG, the price for every running NMR or HPLC is very high :(. I'm in Viet Nam, you know. According a theory, the reaction between anilin & benzaldehyde with Montmorillonite K-10 are take place in 10mns at room temperature. But i don't know why i can't do that.
If you are going to do organic chemistry research access to such instrumentation is an absolute necessity.
Perhaps the yellow oil is your product, at least run an IR.
Place it under High Vac. to remove last traces of solvent, perhaps it will crystallize.
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While an NMR would be useful, TLC is sufficient in this case. Mixing two liquids and getting a liquid is insufficient evidence of success. A TLC should show benzaldehyde disappear and a new spot appear. If you have access to other analytical tools, they too would work, HPLC or GC.
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While an NMR would be useful, TLC is sufficient in this case. Mixing two liquids and getting a liquid is insufficient evidence of success. A TLC should show benzaldehyde disappear and a new spot appear. If you have access to other analytical tools, they too would work, HPLC or GC.
Imines are not too stable towards silica- gel and you can get misleading results.
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Every silica TLC I've seen of an imine has been a terrible streak that yields no useful information. There's not a lot that can go wrong with this reaction so I also think this may be a case of incomplete removal of solvent or one (or both) of the liquid starting materials. Try putting the product under vacuum overnight to see if it solidifies.
Also, a question: Are your starting materials clean? Was your aniline colorless? It can go bad if exposed to light and oxygen yielding nasty yellow or red stuff. Is your benzaldehyde clean? It can oxidize to benzoic acid on standing and I've seen bottles of "benzaldehyde, 99%" that were mostly benzoic acid. If your materials aren't clean you can't expect a reaction to proceed properly.
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I am presuming that the poster's statement the product is a solid indicates this is a literature procedure. None the less, when training students, for example, I liked to advise students to determine whether a reaction had succeeded before working it up. As the poster had indicated, he did not have access to sophisticated equipment. Even with non-sophisticated equipment, can the disappearance of benzaldehyde be monitored? I have succeeded in doing this with TLC. It shouldn't matter greatly if the imine does not chromatograph well. If benzaldehyde does not disappear, I don't think the reaction is working.
Secondly, I too have found that benzaldehyde oxidizes very readily. If a TLC of the benzaldehyde had been done as part of identifying what peaks correspond to starting material, a lack of purity of the benzaldehyde could have been noted.
I have little doubt the product would crystallize if that is what had been reported previously. I am skeptical that the poster's product had sufficient purity to crystallize.
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Yeah, i found out the reason why, because the reation of benzaldehyde with anilin take place in the rate of mol 1:1. But i measured 0.21g benzaldehyde and 0.25g anilin, that means the anilin is residual, then it will react with the product. Now, i measure 0.21g benzaldehyde with 0.18g anilin, and i get the solid product.
I'm very happy. Thank all of you for giving the aids! :x
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Imines are not too stable towards silica- gel and you can get misleading results.
Every silica TLC I've seen of an imine has been a terrible streak that yields no useful information.
This is a moot point now, but I'll share this:
I have used N-Benzylideneaniline before and it actually has a very nice TLC profile. So does 4-methoxy-N-benzylideneaniline. Even N-benzylidene-p-toluenesulfonamide, N-benzylidene-2-pyridinesulfonamide and N-benzylidenedimethylaminosulfonamide, which are much more reactive than aniline derived imines, are stable enough on silica for a decent TLC. N-benzylidene(diphenylphosphoroso)amide can even be purified by silica gel chromatography.