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Author: Subject: Benzoquinone from Paracetamol
DJF90
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[*] posted on 15-1-2017 at 23:37


I would set up for steam distillation and use this property of benzoquinone to advantage. Amarego and Perrin list this as one of the methods for purification, and in your case theres very little else that should pass over.
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JJay
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[*] posted on 16-1-2017 at 01:44


Interesting... I guess you could run the steam distillation like a simple distillation and then extract the product from the distillate?



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DJF90
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[*] posted on 16-1-2017 at 04:29


Benzoquinone is not particularly soluble in water and so should crystallise out. Just collect the distillate, cool in an ice bath to improve the extent of crystallisation and filter to obtain the solids. If further purification is required then sublimation or recrystallisation can be used.
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JJay
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[*] posted on 16-1-2017 at 07:32


Here's the problem with that approach: There's only a small amount of benzoquinone in the reaction mixture, and I'd rather not sacrifice any to mechanical losses. I'm also not relishing the idea of scraping benzoquinone out of my adapters, condenser, and receiver.



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[*] posted on 16-1-2017 at 08:09


I don't think it poses that much of an issue, or it wouldn't be recommended.

See http://www.orgsyn.org/demo.aspx?prep=CV4P0148 for a related compound, also purified by steam distillation (note 12)
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JJay
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[*] posted on 16-1-2017 at 08:18


They did an ether extraction of the distillate (after filtering) to obtain about 20% more product. They also extended the steam distillation longer than absolutely required to flush the adapters and condenser. Of course, this would result in lower yields without doing an extraction on the distillate.

I think the suggestion to steam distill is a good one, but I'm quite certain that it's a good idea to follow it up with a solvent extraction for the reasons previously mentioned.


[Edited on 16-1-2017 by JJay]




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DJF90
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[*] posted on 16-1-2017 at 08:35


You might find that by cooling the distillate in the fridge/ice bath for a few hours might make the solvent extraction unnecessary, but in the first instance a quick extraction with ether or DCM sounds pragmatic.
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[*] posted on 16-1-2017 at 11:47


I followed JJay's little mini-write up for oxidizing paracetemol via KMnO4, but after extracting both portions with 3 portions of DCM the reaction mixture didn't seem to change color/clear-up and after drying and evaporating the combined DCM layers I was left with a small lonely empty beaker :( I kept my reaction mixture just in case anyone has any idea how to extract any possible product out of it
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[*] posted on 16-1-2017 at 14:58


I am not sure if benzoquinone will dissolve in DCM. It does dissolve in ether and chloroform.

Here I have 10.22 grams of slightly pink acetaminophen extracted from pain reliever alongside some potassium permanganate and 60 mL homemade ether.



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[*] posted on 16-1-2017 at 15:12


Quote: Originally posted by JnPS  
I followed JJay's little mini-write up for oxidizing paracetemol via KMnO4, but after extracting both portions with 3 portions of DCM the reaction mixture didn't seem to change color/clear-up and after drying and evaporating the combined DCM layers I was left with a small lonely empty beaker :( I kept my reaction mixture just in case anyone has any idea how to extract any possible product out of it


There is a distinction that I probably should have drawn before... the procedure was not a "write up" - it was a proposal. A writeup should be written in the past tense and have a reported yield. A proposal hasn't actually been tested yet.

I'm reasonably sure that it can be gotten to work. If you have some product in solution, it should be possible to extract it with chloroform, according to the PDF from which I derived the procedure. Other solvents are untested. I am reasonably sure that ether should make a good substitute for chloroform. From a quick search, I didn't see any solid-looking reports where anyone successfully dissolved benzoquinone in DCM, although I don't see any theoretical reason why that wouldn't be possible. I did see one unreferenced comment made on another forum suggesting that it does not dissolve in DCM and a few other comments stating that it does. (Note that I certainly do not possess omniscience with relation to chemistry, so there may very well be a reason that benzoquinone does not dissolve in DCM, but I don't know what it is, if there is one.)


[Edited on 16-1-2017 by JJay]

[Edited on 16-1-2017 by JJay]




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[*] posted on 16-1-2017 at 15:16


I know DDQ dissolves in DCM, and I would expect benzoquinone to have greater solubility. You could probably find an exact value with some searching.



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[*] posted on 16-1-2017 at 15:28


Thanks for the distinction, I'll try to extract it with chloroform tomorrow, guess I finally found a use for my home-made chloroform. :)

If I manage to get some benzoquinone crystals after that, I'll see if I can get them to dissolve in DCM

EDIT: I just realized @JJay, your acetaminophen is slightly pink, mine was too after extraction so I decided to recrystallize from water. I'm pretty sure we used different brand pills so what a coincidence XD




[Edited on 16-1-2017 by JnPS]
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[*] posted on 16-1-2017 at 19:30


I'm ready to start the reaction.

Reading over that paper again, the calculations they made to estimate the Gibbs free energy don't make sense... they calculated a positive Gibbs free energy at 25 C, which would indicate that the reaction does not happen at that temperature... but they clearly show experimental results indicating that the reaction does proceed spontaneously at 25 C....

The reaction clearly happens more quickly at higher temperatures, so slight heating might not be a bad idea. They have tested the reaction at temperatures as high as 55 C.





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[*] posted on 16-1-2017 at 19:45


When I poured in the permanganate, I could see a definite brown color of manganese dioxide forming before the solution went completely dark.

I still had a tiny amount of undissolved permanganate in my 250 ml beaker, so I rinsed it with about 10 ml of water and added it to the reaction.

IMG_20170116_181652.jpg - 433kB




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[*] posted on 16-1-2017 at 20:14


I believed the delta G they were talking about was for the formation of the transition state usually denoted by a 'double dagger' symbol but they used a hashtag instead. A positive delta G for the transition state would explain why slight heating is necessary for the reaction. I don't think they were talking about the overall delta G for the reaction.

I had the same issue with the KMnO4, though I used around 50mL of extra distilled water to wash out the beaker. I also kept the reaction mixture around 40C for five hours and the reaction appeared to be finished when I went to begin the work-up. Can you take a picture of your reaction mixture afterwards? I want to see if the color of my solution matches yours.
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[*] posted on 16-1-2017 at 20:36


I was just reading over the paper to figure out how fast the reaction should go, and I think I found a couple of errors. The units on figure 2 don't seem to make any sense... the log of PAM<sub>0</sub>, the initial molarity of the acetaminophen, can't be positive. Surely they meant mmol/dm<sup>-3</sup>. Also, they mistakenly refer to "dichromate" instead of permanganate on the same page as the figure.

Ignoring those obvious errors and doing some crude estimation that assumes the rate equation is first order, it looks like the half life of acetaminophen is about 7 minutes with the initial permanganate concentration at 35 C. That means the reaction would be about 99% complete in an hour.

There are some particles of manganese dioxide floating around, but mostly, the reaction mixture just looks dark. There is a trace of an oil floating on top of it; it looks almost like a gasoline slick. I'll take a picture, but it won't show anything very interesting....


[Edited on 17-1-2017 by JJay]




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[*] posted on 16-1-2017 at 21:12


Whoah.. after turning off my stirrer, something interesting is happening! The manganese dioxide particles are settling to reveal a brownish/yellowish clear solution that likely contains the product!

IMG_20170116_194808.jpg - 443kB IMG_20170116_200931.jpg - 482kB IMG_20170116_204005.jpg - 466kB

So anyway, I don't know for sure yet, but it looks pretty likely that I have some benzoquinone.

[Edited on 17-1-2017 by JJay]




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


Here's the problem I'm running into with ether: it's too soluble in water! I added 30 mL of ether to the approximately 700 mL of solution, saw two layers form, shook it, and the top layer disappeared! If I add the entire 60 mL, I get a very small layer.

I only had 60 mL of ether, and I'm pretty reluctant to handle a larger quantity in this location, so it looks like I might have to make some chloroform....




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[*] posted on 16-1-2017 at 23:02


@JJay, yes ether is slightly soluble in water, about 3g per 100g of water, so thats why your ether layer dissolved. However, dispare not. You can reduce this figure and the solubility of benzoquinone too by adding salt to the aqueous liquid, up to about 20g per 100ml of aqueous phase but 15g is probably enough in your case. The addition of salt may be sufficient to salt out the benzoquinone anyway.

I tend to try methylene dichloride (dichloromethane) first because it is cheaper and more readily available but is less polar and so not a perfect substitute.
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[*] posted on 16-1-2017 at 23:16


@Boffis: I was seriously considering giving that a try but figured that since the reaction was so simple and the reactants are cheap there was no point really, so unfortunately, it's in an organic waste container outside at this point and I've washed and put away my glassware... I definitely do appreciate that suggestion, though, and I'll have to try again in the near future, perhaps tomorrow.

[Edited on 17-1-2017 by JJay]




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[*] posted on 17-1-2017 at 06:30


Your solution looks more red than mine does, but I don't think color differences are a huge concern. I guess I'll try salting it out first and if I don't get any benzoquinone from that I'll just scrap my reaction mixture and try the reaction again using chloroform for the extraction.
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[*] posted on 17-1-2017 at 08:22


Interesting to see that the protons for the oxydation comes from:
-the phenolic moeity --> phenate
-the hydrolysed acetyl group --> acetic acid

So the pink color may come from excès KMnO4, manganese(II) phenate or acetate :).




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[*] posted on 17-1-2017 at 13:32


The solution actually wasn't pink to my eyes... more of a yellow to brown color. There was a trace of violet on the sides of the beaker from splashing, but that was just KMnO4 and not very much of it... that stuff has an extremely intense color.

Benzoquinone is yellow and tar is brown... but perhaps pink mixed with yellow looks brown... IDK.




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[*] posted on 17-1-2017 at 14:12


I added 120g of salt to my 800mL of solution and It still yielded no yellow precipitate, all I filtered off was a bit of MnO2 dust that remained. I won't be able to be in my lab again until Saturday morning, but I'll re-run the oxidation and try extracting with chloroform. I'll keep an eye on this thread to see if JJay manages to beat me to the benzo

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[*] posted on 17-1-2017 at 17:35


I am swamped with work tonight, but I'll definitely start on it before this weekend.



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