Sciencemadness Discussion Board
Not logged in [Login - Register]
Go To Bottom

Printable Version  
 Pages:  1  2    4  
Author: Subject: Benzoquinone from Paracetamol
Boffis
International Hazard
*****




Posts: 1047
Registered: 1-5-2011
Member Is Offline

Mood: No Mood

[*] 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:

6C<sub>8</sub>H<sub>9</sub>NO<sub>2</sub> + 10KMnO<sub>4</sub> &rarr; 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.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] 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<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.




I'm no longer involved in this forum.
View user's profile View All Posts By User
AvBaeyer
National Hazard
****




Posts: 473
Registered: 25-2-2014
Location: CA
Member Is Offline

Mood: No Mood

[*] 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
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] 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 142 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]




I'm no longer involved in this forum.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5928
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] 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




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
PHILOU Zrealone
International Hazard
*****




Posts: 2879
Registered: 20-5-2002
Location: Brussel
Member Is Offline

Mood: Bis-diazo-dinitro-hydroquinonic

[*] 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.




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)
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] 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.



I'm no longer involved in this forum.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] 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.






I'm no longer involved in this forum.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5928
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] 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 202 times




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
PHILOU Zrealone
International Hazard
*****




Posts: 2879
Registered: 20-5-2002
Location: Brussel
Member Is Offline

Mood: Bis-diazo-dinitro-hydroquinonic

[*] 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.




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)
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] 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.

--





I'm no longer involved in this forum.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 21-1-2017 at 08:19


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.




I'm no longer involved in this forum.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 22-1-2017 at 16:56


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.




I'm no longer involved in this forum.
View user's profile View All Posts By User
JnPS
Hazard to Self
**




Posts: 89
Registered: 29-7-2016
Location: PA, USA
Member Is Offline

Mood: Umpolung

[*] posted on 22-1-2017 at 19:11


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.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 22-1-2017 at 19:28


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]




I'm no longer involved in this forum.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5928
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 23-1-2017 at 13:31


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
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 23-1-2017 at 15:13


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]




I'm no longer involved in this forum.
View user's profile View All Posts By User
Amos
International Hazard
*****




Posts: 1177
Registered: 25-3-2014
Location: Yes
Member Is Offline

Mood: No

[*] posted on 24-1-2017 at 07:12


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.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 24-1-2017 at 22:26


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]




I'm no longer involved in this forum.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5928
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 26-1-2017 at 15:08


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]




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 26-1-2017 at 17:45


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.




I'm no longer involved in this forum.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 3-2-2017 at 23:12


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.




I'm no longer involved in this forum.
View user's profile View All Posts By User
Boffis
International Hazard
*****




Posts: 1047
Registered: 1-5-2011
Member Is Offline

Mood: No Mood

[*] posted on 4-2-2017 at 22:10


@ 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.
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 3321
Registered: 15-10-2015
Member Is Offline

Mood: resigned

[*] posted on 4-2-2017 at 22:31


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]




I'm no longer involved in this forum.
View user's profile View All Posts By User
Boffis
International Hazard
*****




Posts: 1047
Registered: 1-5-2011
Member Is Offline

Mood: No Mood

[*] posted on 5-2-2017 at 04:31


@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.
View user's profile View All Posts By User
 Pages:  1  2    4  

  Go To Top