dormouse (Member)
04-22-00 01:36
No 108518
      Meth from Allylbenzene + MeNH2 + Hg(NO3)2 ... -ReFlux  Bookmark   


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Author  Topic:   Meth from Allylbenzene + MeNH2 + Hg(NO3)2 ... 
ReFlux
Member   posted 09-30-98 03:44 AM          
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I was thinking that aminomerc-demercuration of allylbenzene w/ Hg(NO3)2 + MeNH2 in THF might be an attractive way for hypothetical meth production. Would result in racemic product of course, but otherwise a clean and simple reaction.
What are your thoughts?

-ReFlux


Labrat
Member   posted 09-30-98 09:39 AM          
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What about the anti-Markovnikoff addition product, 1-phenyl-3-methylaminopropane? What makes you think this product won't arise from the aminomercuration-demercuration procedure?
And have you got a good source for your allylbenzene? Or have you found a way to synth it cheap and in large quantities? Lr/


KrZ
Member   posted 09-30-98 02:55 PM          
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I'm definitely very interested, if you or anybody has any ref's please post them and I'll look 'em up and post the good parts!
 
KrZ
Member   posted 09-30-98 03:02 PM          
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1-phenyl-3-methylaminopropane would require more energy to produce, with that methyl adding to a CH2 2nd deg carbon instead of a CH, so as long as the reaction was conducted over a descent period, i.e. at the low end of the conc./temp. range, there wouldn't be much 1-phenyl-3-methylaminopropane formed. You'd still probably get a little bit though, mayb 5-10%. Which I can certainly deal with...
 
ReFlux
Member   posted 09-30-98 05:14 PM          
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KrZ- The ref for this is J. Org. Chem 44,20 Pg 3580-83, 1979.
Some anti-Markownikoff product seems inevitable, but I agree that reaction conditions will play a vital role in that outcome. How do you propose to deal with seperation of the two though? Fractional distillation? Do you have any data on 1-phenyl-3-methylaminopropane? (BP, etc.)

More to come...

ReFlux


Labrat
Member   posted 10-01-98 09:25 AM          
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KrZ: What makes you think that 1-phenyl-3-methylaminopropane is formed like you say? In my opinion, not the addition step , but the reduction is the problem. The mercury-amine complex will add in a Markovnikoff-fashion. But during the reduction, an intermediate aziridine can be formed. This aziridine can be reduced to meth or 1-phenyl-3-methylaminopropane.
Ofcourse you didn't know this, but the ref ReFlux is talking about, performs the reaction at REFLUX temperature. So much for low temps. Lr/


 
KrZ
Member   posted 10-01-98 12:56 PM          
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Doh! I didn't mean methyl adding when I said that... If the mercury-amine complex will add in a Markovnikoff fashion, then the site that it binds to will be so much more reactive it seems like aziridine would be the main by-product rather than 1-phenyl-3-methylaminopropane. Then we could seperate the meth produced from the aziridine and reduce the leftover aziridine (If there was a whole lot of it). It does seem like the aziridine could be a major roadblock, suppose someone will have to dream it before we can know for sure. Reflux at different temperatures from diff. pressures is of course possible and keeping the concentration low would still apply for minimizing 1-phenyl-3-methylaminopropane formation. I should probably suspend further speculation until I check the ref. though.


ReFlux
Member   posted 10-01-98 01:21 PM          
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No aziridines are formed, just anti-markownikoff product, and I tend to agree with Labrat that it is formed during the reduction phase. Any ideas on seperating the two from a reaction mix?
-ReFlux


KrZ
Member   posted 10-01-98 04:55 PM          
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Could someone describe the mechanism in detail so I can understand whats going on exactly? I've only had about 1/3 a sem. of organic so far.
 
Labrat
Member   posted 10-02-98 09:31 AM          
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The mechanism of the aminomercuration-demercuration procedure:
The mercury-salt complexes with the alkene, making it more susceptible for attack by nucleophiles, like amine compounds. Then, the amine adds to the 2-position in the propylchain, the mercury adds on the 3-position.

The next step is to replace the Hg with a hydrogen atom by reduction with sodium borohydride. Because this reduction is performed under basic conditions, aziridines can be formed, which account for the anti-Markovnikoff product. Remember, the aziridines are intermediates, not the final product of the reduction. The final products are amines and maybe some elimination products formed during reduction (safrole).

And it's most certainly a good idea to check the literature. Lr/


ReFlux
Member   posted 10-02-98 09:23 PM          
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Also the possibility exists for the mercury salt to complex with the amine first, and then the two are added to the alkene via direct addition. The exact principle is still not completely understood.
As for the reduction stages, there is believed to be a ligand exchange (OH for whatever salt of the Hg was used, NO3 for eg) followed by reduction, though here too the exact mechanics are not completely understood.

-ReFlux


Labrat
Member   posted 10-04-98 07:14 AM          
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Thanks Reflux for filling in the blanks. But why do you think that the reaction mechanism is not completely understood here. The JOC article says that about the mode of addition of the amine-mercury complex to the alkene. But later articles proved that the slow dissociation of the HgX+ ion from the amine-mercury complex is the rate-limiting step.
The reduction stage is also pretty clear. Like you mentioned, first ligand exchange occurs, then the mercury is exchange for hydrogen by reduction. What is not clear about this? Lr/


ReFlux
Member   posted 10-04-98 06:04 PM          
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I was just conveying the fact that the reaction mechanism(s) have not actually been proven or verified, but are simply theorized at this point. But yes, these would seem to be very valid ways for the process to occur.
-ReFlux


Labrat
Member   posted 10-08-98 10:23 AM          
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That JOC article you mention does indeed state that the reaction mechanism is not clearly understood. But can you remember when we were discussion the possibility of making MDA from safrole by aminomercuration-demercuration. We dug up a lotta refs which pointed out pretty clearly what the reaction mechanism of the aminomercuration-demercuration was. I thought you understood that by now. Lr/
 
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