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Boffis
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@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:
6C<sub>8</sub>H<sub>9</sub>NO<sub>2</sub> + 10KMnO<sub>4</sub> →
6C<sub>6</sub>H<sub>4</sub>O<sub>2</sub> +
6KC<sub>2</sub>H<sub>3</sub>O<sub>2</sub> + 4KOH + 3N<sub>2</sub> + 10MnO<sub>2</sub> +
4H<sub>2</sub>O
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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JJay
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"After complete degradation of acetaminophen, which was
confirmed from no change in absorbance after 90 minutes,
the whole reaction mixture (acetaminophen=2x10<sup>-2</sup>
mol dm<sup>-3</sup> i.e., 0.120gm in 50 ml distilled water and
KMnO<sub>4</sub>=10x10<sup>-2</sup>mol dm<sup>-3</sup> 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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AvBaeyer
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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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JJay
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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 580 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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Magpie
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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
The single most important condition for a successful synthesis is good mixing - Nicodem
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PHILOU Zrealone
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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.
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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JJay
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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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JJay
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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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Magpie
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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 581 times
The single most important condition for a successful synthesis is good mixing - Nicodem
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PHILOU Zrealone
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| Quote: Originally posted by Magpie |
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.
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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JJay
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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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JJay
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I just noticed something that I didn't notice in my last attempt: There is a pale precipitate on top of the dark brown precipitate. I can't see its
color clearly due to the dark solution.
I'm not too sure about what that is... I'd think benzoquinone would be somewhat soluble... with 550 mL of solution and the solubility of benzoquinone
being 11.1 mg/mL at 18 °C... around 6 grams would dissolve... but there are ions in solution... hmm....
I think it is premature to declare victory, but I'm very curious about what the precipitate is.
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JJay
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I haven't forgotten about this, but I've been busy with other things and haven't done the workup yet. I did take out my beaker and take a look at it
earlier, and the solution is visibly much darker than it was previously... it's now almost opaque, and the precipitates are not visible. Not sure
why....
I decanted the contents into another beaker and observed as I was pouring the mixture that there are most definitely two different precipitates: A
dark one that I assume is manganese dioxide and a fluffy lighter one that *hopefully* is benzoquinone.
I'm going to try steam distilling first and then do a solvent extraction if I see any product.
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JnPS
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So the purpose of performing the reaction in an acetate buffer was simply to reduce the solubility of benzoquinone in the reaction mixture? If you get
any product let me know so I can try and repeat the procedure. I'll start looking to buy the vinegar necessary to make the buffer in the mean time
between classes.
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JJay
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The effect of an acetate buffer was to increase the yield from hydrolosys of NAPQI in the paper cited here: http://www.sciencemadness.org/talk/viewthread.php?tid=8250&a...
I tried to make the pH at the midpoint of the oxidation equal to 5.6.
[Edited on 23-1-2017 by JJay]
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Magpie
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I was doing some reading in Groggins, "Unit Processes in Organic Synthesis," 3rd ed (1947), a chemical engineering text. There I found a synthesis
for "quinone." (Quinone is an archaic name for p-benzoquinone.) What surprised me is that the precursor was aniline. Here's the synthesis:
"A mixture of 25 parts aniline, 200 parts of water-white sulfuric acid, and 600 parts of water, contained in a wooden or corrosion-resistant vat, is
cooled by ice or refrigeration. A solution of 25 parts of sodium dichromate in 100 parts of water is then slowly added with agitation, and stirring
continued for 12 hrs. A solution of 50 parts of sodium dichromate in 200 parts of water is then added, and stirring continued until the reaction is
complete. During the whole operation, the temperature is maintained below 5°C through the addition of ice or by refrigeration. Quinone is recovered
by skimming from the surface of the solution and purified by steam distillation.
Oxidation of aniline with MnO2-H2SO4 mixtures is claimed to give 73 per cent yield of quinone (Gibbs, US patent 2,343,768)."
The single most important condition for a successful synthesis is good mixing - Nicodem
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JJay
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Aniline has largely fallen out of favor as a precursor to benzoquinone in the U.S. and Europe due to environmental regulations, but that process is
still widely used in China.
I am curious as to whether the dark color in my beaker is due the formation of a quinhydrone complex between hydroquinone and benzoquinone. I'm not
completely sure what would cause hydroquinone to form in solution, but it seems plausible that some of the NABQI attacked the some of the product and
reduced it to hydroquinone.
I am not sure if I will have time to run the steam distillation today, but I will definitely get to it in the next couple of days.
[Edited on 24-1-2017 by JJay]
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Amos
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For those looking into the NAPQI route, I know there are a lot of p-substituted aniline derivatives in hair dyes that are converted to the
corresponding imine using hydrogen peroxide (the "developer"), so this may be a cleaner method of oxidizing the paracetamol.
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JJay
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After steam distilling off 50 mL of water, I can see that there is definitely a solid floating in it, but it doesn't look very yellow, and there's
very little of it. If I look at the very largest particle, it looks like it might be yellow, but it's hard to be 100% sure under these yellow lights.
The particle is a little bit darker than a piece of typing paper. There might be some benzoquinone here, but it's only maybe a few hundredths of a
gram. I've read that benzoquinone smells like chlorine, and this substance has a sharp smell that reminds me of chlorine if I take a strong whiff
(which I probably shouldn't do), but it reminds me of nitric oxide more than chlorine. The material left in the boiling flask has the same odor, but
it is very weak. Oddly, I don't smell any acetic acid.
There might be a measurable amount of recoverable product here, but I don't have the equipment I would need to handle such tiny quantities, so I guess
I will discard it.
...I just read that benzoquinone smells like a cross between chlorine bleach and burning plastic. That is a more apt description of the smell, but I
didn't see the neon yellow color that is characteristic of benzoquinone, so I am skeptical that the substance that steam distilled over was actually
benzoquinone.
[Edited on 25-1-2017 by JJay]
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Magpie
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| Quote: Originally posted by JJay |
If acetaminophen can be easily de-acetylated by reflux in potassium hydroxide, I think sodium dichromate could be used to oxidize it to benzoquinone.
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This is supported by Cason & Rapoport in their "Laboratory Text in Organic Chemistry," (1950), p. 332.
I quote: "... the best yields of p-benzoquinones are obtained by oxidation of derivatives having amino or hydroxy in para
positions." "Oxidation of crude aminophenol often gives yields of quinone amounting to 80-95 percent..."
[Edited on 26-1-2017 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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JJay
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| Quote: Originally posted by Magpie | | Quote: Originally posted by JJay |
If acetaminophen can be easily de-acetylated by reflux in potassium hydroxide, I think sodium dichromate could be used to oxidize it to benzoquinone.
|
This is supported by Cason & Rapoport in their "Laboratory Text in Organic Chemistry," (1950), p. 332.
I quote: "... the best yields of p-benzoquinones are obtained by oxidation of derivatives having amino or hydroxy in para
positions." "Oxidation of crude aminophenol often gives yields of quinone amounting to 80-95 percent..."
[Edited on 26-1-2017 by Magpie] |
Chem Player posted a video on de-acetylation of acetaminophen with sodium hydroxide: https://www.youtube.com/watch?v=lIw82Vjp0rk It looks as though p-aminophenol is easy to prepare but hard to purify completely.
I only have a small amount of potassium hydroxide and have sodium hydroxide in great abundance. I'm going to be looking at a location where I might be
able to set up a lab next week, so I hope to give it a try.
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JJay
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I'm going to be attempting de-acetylation of acetaminophen this weekend. I plan to follow Chem Player's procedure with a few variations, something
like this:
1. Dissolve 4g NaOH in 25 mL of water and add to a 50 mL flask.
Chem Player used "10 mL of water and an ice cube" to dissolve 4g NaOH and ended up with about 25 mL of solution. So I think this is about the right
amount of water. Chem Player also used a 100 mL flask, but I think 50 mL is sufficient.
2. Add 5g acetaminophen with stirring.
3. Fit the flask with an air condenser and heat on a boiling water bath with stirring until the internal temperature reaches 90 C for an hour..
Chem Player didn't use a condenser and simply heated the flask on a hot plate on low heat. I don't know exactly what temperature is optimal. I suspect
it would be fine to use a small beaker or Erlenmeyer flask directly on a hotplate on low heat with no condenser.
4. Filter the hot mixture and wash the filter cake with a small amount of hot water.
5. Neutralize the mixture to as close to pH 7 as possible with hydrochloric acid.
It's pretty easy to calculate how much hydrochloric acid would be required with a 100% yield. So I'll add that much and then add a little more,
checking the pH as I go if necessary.
6. Chill the mixture to close to 0 C and filter.
At this point, after drying, we will [hopefully] have a crude product. Chem Player attempted to purify theirs by recrystallization and found it
difficult due to decomposition. I don't know for sure, but it may be feasible to simply use the crude product directly to make benzoquinone. If
additional purification is required, perhaps one could simply dissolve the crude aminophenol in a suitable nonpolar solvent and precipitate it as the
hydrochloride salt with dry HCl gas. One possible problem with doing this is that to obtain p-aminophenol freebase, one must neutralize the HCl and
then extract the p-aminophenol somehow, and that might cause additional decomposition. Also, this won't necessarily remove nitrogen-containing
impurities.
I think I'm going to try using the crude product, perhaps with one recrystallization, in an oxidation with sodium dichromate to produce benzoquinone
and see how it works out.
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Boffis
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@ JJay, I wouldn't bother trying to purify the p-aminophenol, its very sensitive to oxidation. Also avoid chloride ions and hydrochloric acid if you
are going to carry out the oxidation to benzoquinone under acid conditions as you tend to generate chlorohydroquinol by the addition of hydrogen
chloride to benzoquinone in aqueous solutions. This compound is then oxidized to chlorobenzoquinone and so on. I use this process deliberately to
generate chloranil. At low temperatures the process tends to stop at mono and dichloro compounds but that make purifying the product difficult and
increases the consumption of oxidant. When I carry out the latter reaction now I boil the paracetamol with 30-32% hydrochloric acid for an hour under
reflux to hydrolyse the acetamido group, cool and then add the saturated solution of oxidizing agent to the reaction mixture so the temperature rises
steadily to about 90 C and then maintain this temperature until chlorine evolution becomes significant, then add some more 36% hydrochloric acid and
reflux for a further 45 to 60 minutes.
In your case the target is benzoquinone so I would use 50-70% sulphuric acid, reflux for an hour, cool and then start adding your sodium dichromate
solution and keep the mixture cool.
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JJay
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| Quote: Originally posted by Boffis | @ JJay, I wouldn't bother trying to purify the p-aminophenol, its very sensitive to oxidation. Also avoid chloride ions and hydrochloric acid if you
are going to carry out the oxidation to benzoquinone under acid conditions as you tend to generate chlorohydroquinol by the addition of hydrogen
chloride to benzoquinone in aqueous solutions. This compound is then oxidized to chlorobenzoquinone and so on. I use this process deliberately to
generate chloranil. At low temperatures the process tends to stop at mono and dichloro compounds but that make purifying the product difficult and
increases the consumption of oxidant. When I carry out the latter reaction now I boil the paracetamol with 30-32% hydrochloric acid for an hour under
reflux to hydrolyse the acetamido group, cool and then add the saturated solution of oxidizing agent to the reaction mixture so the temperature rises
steadily to about 90 C and then maintain this temperature until chlorine evolution becomes significant, then add some more 36% hydrochloric acid and
reflux for a further 45 to 60 minutes.
In your case the target is benzoquinone so I would use 50-70% sulphuric acid, reflux for an hour, cool and then start adding your sodium dichromate
solution and keep the mixture cool. |
Interesting. So neutralizing with hydrochloric acid might not be such a great idea.... I can certainly use sulfuric instead.
Doing the hydrolysis with sulfuric acid could potentially make things easier....
Edit: After thinking this over a bit more, it appears that HCl would likely not present a huge problem if removed before the oxidizer is added. But
yes, chloride ions in the oxidation reaction would lead to problems.
[Edited on 5-2-2017 by JJay]
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Boffis
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@JJay, yes if you free base the aminophenol and then isolate it you'd be fine but its just one more operation in which to loose you primary reactant.
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