kerousel
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How to get rid of -NH2 ?
Like say you have a carboxamide, for instance let's say phenyl carboxamide. How would you get rid of the -NH2 and replace it with a hydrogen?
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kclo4
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Well, hopefully I understand your question properly, so lets see here to replace an amine with a hydrogen you could do the sendmyer reaction
to replace the NH2 with a hydrogen in an amide you'd produce an aldehyde. Carboxylic acids can be made from amides via hydrolysis.
Carboxylic acids can be reduced with some hard to get reducing agents. I think LAH may work for this.
What is the compound you are after? or are you just curious?
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kerousel
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Oh no, I was just thinking of some possible nicotine syntheses and reactions to make them. Thanks.
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JohnWW
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The method that immediately springs to mind, although applicable only to primary aromatic amines, is by initially diazotization - the formation of a
diazonium salt, -N(+)[triplebond]N, of a mineral acid, by reaction of the aromatic amine (commonly obtained by reduction of an aromatic
nitro-compound), dissolved or suspended in a cold aqueous mineral acid, with NaNO2. The diazonium group is fairly easily removed by reactions with
nucleophiles, e.g. by Cl-, Br-, CN-, or most easily I-, in Sandmeyer reactions, resulting in the corresponding halide or nitrile. It should thus be
analogously possible to remove the diazonium group and replace it with hydrogen by reaction with hydride anion, H-, in a suitable anhydrous aprotic
solvent; and this can also be easily done by reaction with aqueous hypophosphorus acid, H3PO2, producing H3PO3 and a mineral acid as byproducts.
But, because in aromatic diazonium salts the N atoms are involved in canonical structures by resonance, as regards applicability to other types of
-NH2 groups, such as those in amides, -C(=O)NH2, which include carboxamides (e.g. the amino acids asparagine and glutamine), and aliphatic amines, the
method is much less certain, unless other functional groups make them "quasi-aromatic". "Phenyl carboxamide" is benzoic acid amide, C6H5-C(=O)NH2, in
which the -NH2 is not directly bonded to the aromatic ring. "Carboxamides" in pharmaceutical chemistry are more complex amides that, as a class, are
used as anti-convulsive drugs, such as carbamazepine, which contains a tertiary N in a 7-membered quasi-aromatic ring, configured =C-N-C(=O)(NH2)-C=.
[Edited on 28-8-09 by JohnWW]
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DJF90
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If phenyl carboxamide is benzamide, then replacing the -NH2 with -H would give you benzaldehyde. I'm not sure if theres a single transformation that
will affect this, although hydrolysis to the acid and then reduction with DIBAH could provide a means of doing so. If you ask me though you're going
the wrong way to get benzaldehyde.
Also, you could dehydrate the amide to the nitrile, and then hydrolyse this to the aldehyde. I'm unsure of the conditions requred (I cant remember)
but Im sure you can find details in elsewhere here or in a textbook.
[Edited on 28-8-2009 by DJF90]
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Klute
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You can reduce nitriles to aldehydes with copper-treated raney nickel. I posted this ref somewhere on the forum.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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DJF90
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I thought there was an aqueous method to do this. I will have to check a couple of books to see if I can find what I thought I saw and then I shall
report back
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turd
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Please learn some organic chemistry and realize that it's about transforming functional groups, not replacing random atoms. Therefore "How to
transform an (aromatic) amide into an aldehyde?" is a good and "How to get rid of -NH2?" is a bad question.
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DJF90
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Couldn't have put it better myself
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