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Topic: What imines are stable?  (Read 12351 times)

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Offline Enthalpy

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What imines are stable?
« on: April 20, 2015, 01:45:53 PM »
Hello nice people!

I've just read that C=N isn't stable, so:
what hydrocarbyl does it need where to get reasonably stable, as kg amount of concentrated substance?

Thanks!

Offline pgk

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Re: What imines are stable?
« Reply #1 on: April 20, 2015, 02:31:23 PM »
Imines are stable under anhydrous conditions or in anhydrous organic solvents. Contrary, imines are easily hydrolyzed to the initial amine and the carbonyl compound, in aqueous medium. Imine hydrolysis is fast under acidic or Lewis acid catalysis. Under neutral or alkaline conditions, imine hydrolysis is relatively slow.
In other words, the nature of “hydrocarbyl” radical does not play a very important role towards imine hydrolysis. Anyway, due to steric hindrance ketone imines are a little less unstable than aldehyde imines, towards hydrolysis. Also, long chain and fatty hydrocarbyl imines that are hydrophobic, are relatively more stable than short chain and hydrophilic hydrocarbyl imines, towards hydrolysis.
« Last Edit: April 20, 2015, 03:40:08 PM by pgk »

Offline pgk

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Re: What imines are stable?
« Reply #2 on: April 20, 2015, 02:39:25 PM »
Also, Imines are substrates of pericyclic reactions. This must seriously be taken in account to the choice of an appropriate solvent for imines and storage conditions (absence of double bonds, storage in non-transparent containers, etc.).

Offline Enthalpy

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Re: What imines are stable?
« Reply #3 on: April 21, 2015, 01:26:57 PM »
Thanks!

Hydrolysis wouldn't be too much of a threat... But methanamine, pure and alone, is unstable. So what kind of groups at what position make bigger imines stable? Does a methyl on the nitrogen suffice?

Offline pgk

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Re: What imines are stable?
« Reply #4 on: April 21, 2015, 02:17:33 PM »
Probably, you mean methynimine or (wrongly) methenamine (CH2=NH)
Imines prepared from ammoniac are instable and polymerize to polyamines.
Furthermore, imines prepared from formaldehyde (and paraldehyde) are instable and further form perhydro-s-triazines.
In addition, imines prepared from ammoniac and formaldehyde (and paraldehyde) are instable and further form hexamethylenetetramine (empirically called methenamine, too. So, take care of confusions).
Therefore, you need alkyls in both nitrogen and methyne groups.
Whether aldehyde or ketone imines, depends on the desired hydrolytic stability.
Aldehyde imines are easily prepared from both primary and secondary amines. The same for ketone imines from primary amines. Contrary, it is very difficult to prepare ketone imines from secondary amines.
Addition of bulky alkyl groups increases resistance to pericyclic reactions.

Offline pgk

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Re: What imines are stable?
« Reply #5 on: April 21, 2015, 03:11:04 PM »
And a last thing: Formation of aldehyde imines from 2-tertiary or aromatic aldehydes avoids isomerism to enamines, if the latter bothers you.

Offline Enthalpy

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Re: What imines are stable?
« Reply #6 on: April 22, 2015, 03:14:45 PM »
My bad, I meant methanimine H2C=NH.
So, both C and N must be substituted, if I understand properly.
Thanks!

Offline pgk

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Re: What imines are stable?
« Reply #7 on: April 22, 2015, 07:47:32 PM »
Exactly.
Sorry for the nomenclature confusions. But this is what it is, due to a mixture of empirical names.

Offline Enthalpy

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Re: What imines are stable?
« Reply #8 on: April 23, 2015, 03:03:47 AM »
Thank you!
I'll have to go more deeply with imines, maybe find course material online.

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