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Author: Subject: Benzoquinone from Paracetamol
Boffis
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[*] posted on 18-1-2017 at 11:14


@JJay and JnPS, have you considered the reaction that is actually occurring and its stoichiometry. The paper you posted on the 17th Dec is short on actual experimental detail as it is not really about the preparation of benzoquinone but rather about the distruction of paracetamol and other pharmaceuticals in waste water, hence while KMnO4 may be used in excess it is also carried out in very dilute soutions. I have tried to work out a plausible reaction scheme and come up with the following equation:

6C8H9NO2 + 10KMnO4 → 6C6H4O2 + 6KC2H3O2 + 4KOH + 3N2 + 10MnO2 + 4H2O

The products other than benzoquinone are potassium acetate, potassium hydroxide, nitrogen and Mn dioxide.

From this equation is follows that for 1.2g of paracetamol roughly 2g of KMnO4 are required, about half the amount you used. While benzoquinone is fairly resistant to further oxidation it is not indistructable. Your large excess of oxidant may break the benzoquinone down to oxalic acid and similar compounds. In support of this idea is the red-purple solution you obtained; the Mn3+ oxalato complex is of about this colour.

So the problems you are having isolating the benzoquinone may be due the the facr that there isn't much there! I suggect you try the reaction again with less permanganate.
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[*] posted on 18-1-2017 at 11:50


"After complete degradation of acetaminophen, which was
confirmed from no change in absorbance after 90 minutes,
the whole reaction mixture (acetaminophen=2x10-2
mol dm-3 i.e., 0.120gm in 50 ml distilled water and
KMnO4=10x10-2mol dm-3 i.e., 0.400gm in 25 ml distilled
water) was extracted with 50 ml chloroform. The
chloroform layer was washed with 350 ml distilled water.
Chloroform was evaporated and the product obtained was
crystallized. The product obtained was compared with benzoquinone
by spot method.[27] Melting point of these crystals
was similar to that of benzoquinone (m.p.=114–116C).
Sultan also suggested similar products by using different
oxidant.[28] Free radical formation was confirmed following
the literature method.[29] Product formation was further
supported by detection of ammonium ions in solution that
was verified by spot test.[28]"

I think the suggestion to try again with less permanganate is a good one. The excess permanganate is being consumed somehow or the solution would be dark purple when the reaction completes, and if it's being consumed destroying the benzoquinone, that's almost certainly not desirable.




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[*] posted on 19-1-2017 at 15:32


I have read the paper posted by JJay a while back. It is truly not useful as the basis of a synthetic method for obtaining benzoquinone from paracetamol. The mechanism that is proposed in the paper at step 9 (hydrolysis of N-acetylamidobenzoquinone imine [NABQI] to benzoquinone) makes no sense whatsoever. NABQI is a notoriously unstable compound unless special precautions are taken during it synthesis. It is an extremely electrophilic compound among other things. The information given in the paper (quoted in the above comment by JJay) is completely indeterminant. The product was compared to benzoquinone by a spot test but no result is stated. The product had a melting point "similar to benzoquinone" - a garbage statement. Despite all the effort being put into this KMnO4 oxidation, I suspect that you are not going to find success.

See the following for some insight:
Tet. Lett. 1980, v21, 4947
J. Med. Chem. 1982, v25, 885

There is a lot more if you do a Google scholar search.

AvB
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[*] posted on 19-1-2017 at 16:20


Quote: Originally posted by AvBaeyer  
I have read the paper posted by JJay a while back. It is truly not useful as the basis of a synthetic method for obtaining benzoquinone from paracetamol. The mechanism that is proposed in the paper at step 9 (hydrolysis of N-acetylamidobenzoquinone imine [NABQI] to benzoquinone) makes no sense whatsoever. NABQI is a notoriously unstable compound unless special precautions are taken during it synthesis. It is an extremely electrophilic compound among other things. The information given in the paper (quoted in the above comment by JJay) is completely indeterminant. The product was compared to benzoquinone by a spot test but no result is stated. The product had a melting point "similar to benzoquinone" - a garbage statement. Despite all the effort being put into this KMnO4 oxidation, I suspect that you are not going to find success.

See the following for some insight:
Tet. Lett. 1980, v21, 4947
J. Med. Chem. 1982, v25, 885

There is a lot more if you do a Google scholar search.

AvB


According to this paper, p-benzoquinone is obtained from hydrolysis of NABQI.

I definitely think it's worth another try.


Attachment: ja00194a046.pdf (1.2MB)
This file has been downloaded 16 times

Edit: I'm still reading over this paper to try to avoid making any erroneous conclusions and to try to determine experimental conditions.

[Edited on 20-1-2017 by JJay]




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[*] posted on 19-1-2017 at 16:52


speculation:

Could the acetyl group be removed (as in a protective group removal) leaving p-aminophenol? From there one could diazotize then acidify to form the 2nd OH group, giving hydroquinone. Benzoquinone should be easy from there, if desired.

http://www.synarchive.com/protecting-group/Amine_Acetamide




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[*] posted on 20-1-2017 at 05:14


Quote: Originally posted by Magpie  
speculation:

Could the acetyl group be removed (as in a protective group removal) leaving p-aminophenol? From there one could diazotize then acidify to form the 2nd OH group, giving hydroquinone. Benzoquinone should be easy from there, if desired.

http://www.synarchive.com/protecting-group/Amine_Acetamide

p-amino-phenol will yield a relatively stable diazo-phenoxide...concentrated acid will simply make the diazonium back. See DDNP tread into energetic material section

Hydrolysis of paracetamol is exposed into that vast tread as a starting material for iso-para-diazo-dinitrophenol.

I think that maybe to submit p-amino-phenol to water hydrolysis into the warm (acidic or basic?) will take the NH3 off.
Because phenols as their name indicates are enols...and so anilins are enamines...as discrete transcient structure
-CH=C(-OH)-CH= <----> -CH2-C(=O)-CH=
-CH=C(-NH2)-CH= <----> -CH2-C(=NH)-CH=
This is proven by much specific organic reactions like picric acid (trinitrophenol) conversion to picramide (trinitroanilin) with NH3; or like the formation of cyclohexan-trion-trioxime from phloroglucidol (1,3,5-trihydroxybenzen) and hydroxylamine.




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[*] posted on 20-1-2017 at 13:14


It might be met with utter failure, but I am going to make an attempt at oxidizing acetaminophen again tonight in an acetate buffer with a stoichiometric amount of permanganate.



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[*] posted on 20-1-2017 at 14:01


Quote: Originally posted by Magpie  
speculation:

Could the acetyl group be removed (as in a protective group removal) leaving p-aminophenol? From there one could diazotize then acidify to form the 2nd OH group, giving hydroquinone. Benzoquinone should be easy from there, if desired.

http://www.synarchive.com/protecting-group/Amine_Acetamide


If acetaminophen can be easily de-acetylated by reflux in potassium hydroxide, I think sodium dichromate could be used to oxidize it to benzoquinone. DJF90 pointed out earlier this oxidation of a chlorinated aminophenol to benzoquinone with sodium dichromate, and the researcher mentioned in the notes that he's prepared benzoquinone by this same reaction at 5-10 C: http://www.orgsyn.org/demo.aspx?prep=CV4P0148

Other oxidants might work too.






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[*] posted on 20-1-2017 at 16:12


Quote: Originally posted by PHILOU Zrealone  

p-amino-phenol will yield a relatively stable diazo-phenoxide...concentrated acid will simply make the diazonium back.


Thanks PHILOU for your comments. I don't have the depth of knowledge about diazotization to add much here. I understand that diazonium ions can couple with themselves if sufficiently electron rich as I imagine a phenol might be.

This link shows a Chinese patent that purports to use this technology to make resorcinol. Using the patent translator I converted this to English from Chinese. Then I went a step further and converted the "Example 1" into English usable to me. This is shown in the attached Word file.

Do you think this patent is untrustworthy?


Attachment: Preparation of Resorcinol CN105601476.doc (30kB)
This file has been downloaded 11 times




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[*] posted on 20-1-2017 at 17:55


Quote: Originally posted by Magpie  
Quote: Originally posted by PHILOU Zrealone  

p-amino-phenol will yield a relatively stable diazo-phenoxide...concentrated acid will simply make the diazonium back.


Thanks PHILOU for your comments. I don't have the depth of knowledge about diazotization to add much here. I understand that diazonium ions can couple with themselves if sufficiently electron rich as I imagine a phenol might be.

This link shows a Chinese patent that purports to use this technology to make resorcinol. Using the patent translator I converted this to English from Chinese. Then I went a step further and converted the "Example 1" into English usable to me. This is shown in the attached Word file.

Do you think this patent is untrustworthy?



It is trustworthy...

Meta-amino-phenol doesn't form diazo-oxides; only ortho-amino-phenol and para-amino-phenol do.
If you read the DDNP tread, you will see that the formation of diazo-oxide seems to have a link with (require) the possibility of a quinonic structure formation...while p-quinon or o-quinon are possible; m-quinon is not.

For the same kind of reason, you get benzotriazole from o-diamino-benzen diazotation and another weird imino-diazo-compound from p-diamino-benzen and no or with difficulty bis-diazoniums...while m-diamino-benzen provides exclusively the bis-diazonium (and coupling products if accessible positions onto another aminobenzenic molecule; or triazenes if position unavailable).

Diazoniums are really strange and fascinating weird beasts.




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[*] posted on 20-1-2017 at 22:55


I think this is the balanced equation for oxidation of acetaminophen to NAPQI:

2 C8H9NO2 + KMnO4 -> 2 C8H7NO2 + KOH + MnO2 + H2O

Here's what I'm about to try:

--

Place 3.64 grams of sodium bicarbonate in a 1000 mL beaker. Add 50.00 mL 5% distilled vinegar. Dilute the resulting buffer to 500 mL with distilled water and dissolve 1.20 grams acetaminophen in it then cool to 0C on an ice bath.

Dissolve 0.63 grams potassium permanganate in 50 mL distilled water and chill to 0C.

Mix the two solutions thoroughly and allow to slowly warm to room temperature, then filter and extract the product with a suitable solvent.

--





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