Picric-A
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Alternative Oxidisers in Skraup reaction
I am trying to synthesise some Quinoline from Phenylamine and glycerol however we dont have any Nitrobenzene and the school will only be ordering some
in a month.
Are there any oxidisers (exept arsenic acid!) that would work for this? Must they be organic oxidisers? I guess something like H2O2 would just oxidise
the Phenylamine.. 
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JohnWW
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The Skraup Synthesis of quinoline (1-aznaphthalene) seems to be well-covered in the organic textbooks. Aniline is heated with glycerol,
CH2(OH)-CH(OH)-CH2(OH), in the presence of H2SO4 and an oxidant. Various oxidants have been used, including (according to the textbooks) nitrobenzene
and air. The mechanism consists of 5 steps: acid-catalyzed partial dehydration (-2H2O) of the glycerol to propenaldehyde, Michael addition of this to
the -NH2 group (which loses an H), acid-catalyzed reduction of the aldehyde group to -OH, ring closure with loss of H+, dehydration of the cyclic
amino-alcohol to form a cyclic secondary amine with a double bond conjugated to the benzene ring (dihydroquinoline), then oxidative removal of the H
on the N and an adjacent H with aromaticization.
It is in the last step only that moderate oxidation is required. Besides air or O2 (which could be simply bubbled in under pressure) or a
nitro-compound like nitrobenzene, I suppose H2O2 or a peroxy-acid would probably do. Chromate/dichromate may also do, but there would probably be the
danger of the resulting Cr(III) forming a complex with the quinoline. Stronger oxidants are liable to cleave the double bond in the dihydroquinoline
instead.
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entropy51
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It is said here http://curlyarrow.blogspot.com/2009/01/skraup-reaction-how-t...
that NaI can be used in place of nitrobenzene, but I'm too dislexic to know if it will work or not. But I LOVE the idea of you doing a Skraup! Wear
a hat.
Better to remain silent and appear a fool than to open your mouth and remove all doubt.
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Klute
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Hehe, entropy, your sarcasm is actually pretty funny.. I like the picture of wearing a hat 
\"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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entropy51
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The smell of quinolines is very difficult to wash out of one's hair. Trust me.
It would be interesting to know if NaI actually works. Mr. Picric could make a contribution if he could tell us.
Better to remain silent and appear a fool than to open your mouth and remove all doubt.
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JohnWW
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What are you going to use the quinoline for? I suppose one use would be to form quaternary ammonium salts by reaction with reagents which release
carbocations, e.g. organic halides; these salts are potent antiseptics and fungicides and in some cases herbicides (and also have a strong distinctive
smell).
See http://en.wikipedia.org/wiki/Quaternary_ammonium_cation
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Paddywhacker
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In those conditions the H2SO4 will oxidize the iodide to I2, which should be perfectly adequate as the mild oxidizing agent required by the reaction.
And the I2 would be quickly regenerated, explaining why only catalytic amounts of NaI are required.
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not_important
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Besides substituted nitrobenzenes and the aforementioned iodine/iodide, ferric compounds and V2O5 have been used; nitrobenzenes and arsenate give the
best yields though.
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Paddywhacker
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A side question is what is the nitrobenzene reduced to? ... azobenzene?
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JohnWW
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The nitrobenzene used as a mild oxidant in the final step would most likely be reduced to nitrosylbenzene, and possibly then to phenylamine in view of
the fact that 2 Hs are removed in the final oxidation. If this second reduction occurs, it would be a source of phenylamine for repetition of the
synthesis.
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panziandi
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I have a nagging feeling that some vanadium compound also works, perhaps V2O5... should have some of the stuff I sent you left, so long as Saber
didn't use it all in his contact plant.
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Picric-A
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Yep unfortunatly i did use most (about a gram left) of the V2O5 on a catalyst but i am at school now so i guess the school will have some.
The iodide route seems pleasing as only a catalytic amount is needed and i know the school has iodides.
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entropy51
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You're welcome. All three of you. You can come down off the porch long enough to Skraup yourself.
Better to remain silent and appear a fool than to open your mouth and remove all doubt.
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stateofhack
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This thread is hilarious.
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entropy51
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We don't hate each other nearly so much when we're laughing.
We even managed to sneak in some interesting chemistry.
[Edited on 10-9-2009 by entropy51]
Better to remain silent and appear a fool than to open your mouth and remove all doubt.
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JohnWW
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P.S. to my post of yesterday on this thread:
Further possible uses of quinoline, when you have made the stuff: see http://en.wikipedia.org/wiki/Quinoline
Extract:
Quinoline is mainly used as a building block to other specialty chemicals. Approximately 4 tonnes are produced annually according to a report
published in 2005. Its principal use is as a precursor to 8-hydroxyquinoline, which is a versatile chelating agent and precursor to pesticides. Its 2-
and 4-methyl derivatives are precursors to cyanine dyes. Oxidation of quinoline affords quinolinic acid (pyridine-2,3-dicarboxylic acid), a precursor
to the herbicide sold under the name "Assert".[1 - Gerd Collin, Hartmut Höke "Quinoline and Isoquinoline" Ullmann's Encyclopedia of Chemical
Technology; 2005 Wiley-VCH, Weinheim].
Quinoline was first extracted from coal tar in 1834 by Friedlieb Ferdinand Runge. Coal tar remains the principal source of commercial quinoline. There
are several other methods for its synthesis besides the Skraup reaction ( http://en.wikipedia.org/wiki/Skraup_synthesis , using ferrous sulfate, glycerol, aniline, nitrobenzene, and sulfuric acid). The others, linked in
the Wikipedia article, are:
* Combes quinoline synthesis using anilines and β-diketones.
* Conrad-Limpach synthesis using anilines and β-ketoesters.
* Doebner-Miller reaction using anilines and α,β-unsaturated carbonyl compounds.
* Friedländer synthesis using 2-aminobenzaldehyde and acetaldehyde.
* Povarov reaction using an aniline, a benzaldehyde and an activated alkene.
* Camps quinoline synthesis utilizing an o-acylaminoacetophenone and hydroxide
* Knorr quinoline synthesis, using a β-ketoanilide and sulfuric acid.
* Gould-Jacobs reaction starting from an aniline and ethyl ethoxymethylenemalonate
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entropy51
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John, I see your list includes the Doebner-Miller synthesis of quinolines. That reaction is much better behaved than the Skraup (legendary for
runaways). I once ran the Doebner-Miller many times on a very large scale and there was never a problem with runaways. I would never have tried the
Skraup on a large scale.
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