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BobHawson
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PABA > Aniline
How would one one convert PABA (paraaminobenzoic acid) into aniline?
BobHawson
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kclo4
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Decarboxylating its salt with sodium hydroxide would probably work.
[Edited on 1-3-2009 by kclo4]
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Sauron
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Decarboxylate the PABA without oxydizing the readily oxidizable amino group, which would be a difficult trick.
As you were informed when you started a thread on acetaminophen -> aniline, you are driving against the traffic and on wrong side of the road.
Both are difficult transformations. Particularly in presence of a sensitive group.
Better to obtain or make benzoic acid, decarboxylate that to benzene, nitrate that to nitrobenzene and reduce that to aniline.
All of those are easy well documented transformations.
If you can acquire benzene or nitrobenzene directly do so. Hoppe's #8 bore solvent for cleaning the rifling of firearms is mostly nitrobenzene, you
might try distilling that (in a fume hood or outside.)
Toluene boiled with potassium permanganate solution will get you benzoic acid.
Benzoic acid -> benzene has been subject of a thread, UTFSE.
Ordinary nitrating mixture (conc sulfuric and conc nitric acids in correct proportions and amounts) gets nitrobenzene, again outside or in a hood,
nitrobenzene is harmful.
Tin and conc HCl reduces nitrobenzene to aniline, much more harmful than nitrobenzene, be warned!
Sic gorgeamus a los subjectatus nunc.
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kclo4
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What Sauron said is the smartest thing to do, but perhaps you could oxidize the PABA to 4-nitrobenzoic acid and then decarboxylate that and then
reduce it. I don't think the NO2 would survive though, but it seems like a possibility.
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Sauron
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My expectation would be a flask full or tar.
Protecting the NH2 with formyl, benzoyl or acetyl might help but somehow I doubt the thread author has formic acid, benzoyl chloride or Ac2O on hand.
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kclo4
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I'm curious, what would the tar contain, or how would the tar form?
Would the nitro group oxidize parts of the molecule, or form a salt similiar to how nitromethane and sodium hydroxide do?
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Sauron
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I am referring to the oxidation of PABA to p-nitrobenzoic acid. That sounds like a tar baby to me.
If you managed to get isolated 4-nitrobenzoic acid then there is no reason to expect further tar formation.
Reducing aryl nitro compounds to amines is facile, but oxidizing arylamines to nitro compounds is generally not a piece of cake. Last time I looked
into this a rather costly catalyst was advised.
[Edited on 2-3-2009 by Sauron]
Sic gorgeamus a los subjectatus nunc.
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BobHawson
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Could you please link to the thread covering benzoic acid into benzene? I was unable to find it.
And couldn't you get benzoic acid from sodium benzoate with HCl as well as from toluene and potassium permanganate?
BobHawson
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not_important
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Benzene summary thread
https://sciencemadness.org/talk/viewthread.php?tid=4902
And rather than
benzoic acid => benzene => nitrobenzene => aniline
I would consider
benzoic acid => ammonium benzoate => benzamide => aniline
the conversion to amide being done by heating with B(OH)3 catalyst in xylene, the water formed being azeotroped off. Chlorine bleach will convert the
amide to aniline.
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Formula409
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Why not just start with Sodium Benzoate?
http://www.sciencemadness.org/member_publications/benzene_pr...
Formula409.
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thirdharmonic
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"Decarboxylate the PABA without oxydizing the readily oxidizable amino group, which would be a difficult trick."
im not doubting it, but i dont understand. like the C02H group oxidizes the amine to the Ph-N-N-Ph diazo hydrazine thing? and in turn goes to
aldehyde?
i thought some copper salts eased decarbyoxylation, but i dont really understand the mechanism behind decarboxylation, ionic..radical..i dont know
an acidic solution in a very high boiling point solvent like glycerin and the protonated amine should be effectlivly inert, no?
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Sauron
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CORRECTION
Upthread I stated that a commercial product for cleaning the bores of firearms, Hoppe's #9, is primarily nitrobenzene.
This is erroneous.
Maybe it was true at one time, but I just looked up the MSDS for this product and it contains no nitrobenzene at all.
It is composed of kerosene, ethanol, amyl acetate, xylene, NH4OH, and other ingredients.
We used to refer to this as "Nitro" in the old days and it smelled of nitrobenzene strongly. I also used a great deal of surprus military bore
cleaner, same smell. These were not kerosene and alcohol and banana oil etc.
Anyway I just wanted to go on record that harvesting nitrobenzene from this product is a nonstarter.
[Edited on 2-3-2009 by Sauron]
Sic gorgeamus a los subjectatus nunc.
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Nicodem
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In literature there are only examples using the Cu/quinoline method for decarboxylating p-aminobenzoic acids (for example: Synthesis (1985)
778-779; JACS, 129 (2007) 4824-4833).
You can't just heat a carboxylic acid and expect it to decarboxylate just like some magic thing. There must be a viable mechanism, either a SET
mechanism as in Cu/quinoline method or one of the several other mechanistic possibilities, but all are substrate specific (none is general).
PS: I'm moving this thread to the Beginnings section due to the original poster not using references and obviously not using neither the search engine
or literature.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Globey
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BobHawson,
One of the dead giveaways you have an old nitro bore cleaner, is the smell is very similar (yet peculiarly different) than benzaldehyde. Still, it is
similar enough that if you have old bore cleaner, and it smells like bitter almonds, you probably have the old nitro formulation. If you look in the
reagent aq section, you can see benzoic acid is readily available from cider mill supplies.
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Siddy
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PABA > p-nitrobenzoic acid clean and easy with acidic dichromate, very standard procedure - consult vogels.
No tar, 70% yield, did it in second year as the first step to semi-synthetic benzocaine.
[Edited on 5-3-2009 by Siddy]
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PHILOU Zrealone
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Maybe by Kolbe electrolysis...?
Aromatic carboacid decarboxylate in such conditions...while aliphatic do a kind of dimerisation...
2R-CO2H --> R-R + 2CO2 + H2
C6H5-CO2H --> C6H6 + CO2
...so maybe?
H2N-C6H4-CO2H --> C6H5-NH2 + CO2
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Random
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What is obtained by electrolysis of sodium p-aminobenzoate? Maybe amino group wouldn't survive, but sodium p-nitrobenzoate could be electrolysed to
make nitrobenzene?
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draculic acid69
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Quote: Originally posted by Nicodem  | In literature there are only examples using the Cu/quinoline method for decarboxylating p-aminobenzoic acids (for example: Synthesis (1985)
778-779; JACS, 129 (2007) 4824-4833).
You can't just heat a carboxylic acid and expect it to decarboxylate just like some magic thing. There must be a viable mechanism, either a SET
mechanism as in Cu/quinoline method or one of the several other mechanistic possibilities, but all are substrate specific (none is general).
PS: I'm moving this thread to the Beginnings section due to the original poster not using references and obviously not using neither the search engine
or literature. |
Does anyone else believe this or have doubts?
https://m.youtube.com/watch?v=S0T-sR-nn2Y
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zed
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So.... Perhaps it would be better to actually try an experiment, rather than just declare an endeavor impossible?
I always figured it was possible. I just didn't like the high price of PABA.
I like the experimental technique. Even though, I'm a little rusty, I think I could handle it.
Another positive... No shipping problems! Lord knows what hazard fees might be for shipping Aniline.
One of the supplement companies, is selling PABA at $47.00 US/kilo....
Oh, and thank you for your post.... It was illuminating.
Well enough, for some Gold to be out there.. Somewhere.
Very helpful, for someone to find it, and holler "Eureka!"
Swiped from Draculic.... https://m.youtube.com/watch?v=S0T-sR-nn2Y
[Edited on 3-3-2021 by zed]
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draculic acid69
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I always wondered if this would work but I always thought of
Na benzoate+NaOH = benzene so
PABA+NaOH = aniline
Thing is in the video no base is used so I was dubious.
But if it works awesome.
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zed
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Well, my concern would have been polymerization. That is what happens, when you heat Glycine neat.
Yes, Glycine does decarboxylate... Some. But, it also produces a flask containing plenty of brown crud. And, a distillate of semi-solid white
material, appearing to be principally Methylamine Carbonate.
Perhaps PABA's aromatic amino-group is less subject to amidization. That demo looked like a pretty clean conversion.
The thermal decarboxylation of Niacin works to produce Pyridine, though it requires a catalyst to work well.
And, the Nitrogen present is less vulnerable to attack.
The procedure looked pretty legit to me. Why would this guy fake it?
I'd like to give it a test run. Just because I have wondered about it for so long. But, if It actually works as advertised... Well, then I'd have
Aniline on my premises. And, I don't want Aniline on my premises. At least, I don't think I do.
Hmmm. Poisonous. Oily liquid. No earthly use for it. Oh, wait a second. I could use it to make Phenyl Hydrazine. Easy make, and it might be
relatively difficult to buy now. I 've got a lingering interest in the Fischer Indole synthesis.
Always wondered what pure Skatole really smells like.
Hmmm. Maybe I'll try it. There is a nifty new method for producing Phenyl Hydrazines. Involves reducing a Benzene Diazonium salt, with ascorbic
acid.
So... Easy Aniline.
Guess I better check on the availability of Phenyl Hydrazine.
[Edited on 4-3-2021 by zed]
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draculic acid69
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Im just amazed at how many ppl have thought of paba to aniline but no one has tried it until now.
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draculic acid69
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After asking if anyone else has done this or does he have any posts, papers, references etc of anyone actually doing this before ( lots of ppl have
theorised this but no actual experiments) I got this reply where he says other ppl have replicated it and it has a the corresponding products made
from it and has the same rxns as aniline so I'm satisfied it's genuine aniline formed.im convinced it's legit: here's the response:
One the reasons I wanted to film this was because I hadn't seen it done before and it's practically useful for the amateur chemist. I started looking
into this reaction about two years ago after running the decarboxylation of niacin to pyridine, I figured that a similar thing could be done for paba
to aniline. I was unable to find any papers using simple thermal decarboxylation of paba but I did find similar papers demonstrating the thermal
decarb of anthranlic acid to aniline here: https://cdnsciencepub.com/doi/pdf/10.1139/v52-065 In early 2019 first tried decarboxylation in aqueous H2SO4 but I only got a tiny yield of what I
presumed to be aniline from its immiscibility in water and subsequent solubility in acid. Moving onto thermal decarb, I then figured that I may as
well try just heating the solid before experimenting with adding Cu chromite or anything else. To my surprise, I found that simple thermal decarb
yielded an oily liquid with chemical and physical properties corresponding to aniline. I've used the aniline from this to make quinoline and
phenylhydrazine which I then made into tetrahydrocarbazole in another video, also the product has a hypergolic reaction with nitric acid. My procedure
has been replicated by a number of people on Explosions&Fire's discord server as well.
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wg48temp9
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Below is a link to the first page of a 1963 article describing the decarboxylation of molten PABA and other acids. Unfortunately I can not retrieve
the full article at the moment.
https://pubs.acs.org/doi/abs/10.1021/j100795a033
I am wg48 but not on my usual pc hence the temp handle.
Thank goodness for Fleming and the fungi.
Old codger' lives matters, wear a mask and help save them.
Be aware of demagoguery, keep your frontal lobes fully engaged.
I don't know who invented mRNA vaccines but they should get a fancy medal and I hope they made a shed load of money from it.
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Fyndium
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The most common things are:
1) People speak about something, but their life carries on and they never return to it, or
2) they come asking, meanwhile gather data on the web, try it and make it work, they either need it for some purpose or something, and never return to
tell here that they got it working, because they got what they wanted.
I find it annoying that people come to be spoon-fed for some synthesis, but never input any of their own info. I've slowly gained a decent info on all
of the basic stuff and still going on, and every now and then I come up with these simple, otc synthesis for useful reagents and memorize them.
I suppose I'm gonna write up a bunch of synthesis during this year once I get everything else in my life order and make some time. I've already got a
list ready.
-
But, as salicylic acid readily decarboxylates to phenol, and niacin turns into pyridine with help of a little catalyst, this would be a logical
continuation.
[Edited on 4-3-2021 by Fyndium]
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