xwinorb
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toluquinone reduction
The quoted text below is for making toluhydroquinone from toluquinone.
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Dissolve or suspend 10 grams of p-toluquinone in 2M HCl, and add a little Zinc powder. When the solution is colorless, filter, neutralize with NaHCO3,
extract the dihydric phenol with ether, and evaporate the solvent.
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I have a few questions :
It is not very informative regarding the necessary ammount of HCl and zinc. Looks like it is a zinc/HCl reduction, and so I guess it would need at
least a few equivalents of each.
Could someone please suggest adequate ammounts of each ?
"A little zinc powder" is too vague.
For nitrostyrene reduction with zinc, the ammount I use is 5:1 by weight. I guess it could be divided by 3 here.
Each mole of quinone would need two atoms of H, while in the nitrostyrene reduction each mole of the nitrostyrene needs 6 atoms of H. So I guess OK to
divide by 3.
EDIT : Sorry, I think more exactly the nitrostyrene needs 8 H atoms to be reduced. EDITED by XW.
What would be a minimum ammount of HCl ?
Any further commenst or suggestions would be greatly appreciated.
[Edited on 10-3-2010 by xwinorb]
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xwinorb
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I have the impression this does not work for quinones. Sorry for this post.
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Lambda-Eyde
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Are you familiar with the mole concept?
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turd
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This is a little bit cryptic - you want to reduce plain benzoquinone to hydroquinone? A weird notion to me since I always go the other direction, but
check out for example
J. Chem. Soc., Perkin Trans. 1, 1989, 8, 1555-1556
| Quote: | | Are you familiar with the mole concept? |
Have you ever done Zn/HCl or Al/Hg reductions? The metal is usually in (a large) excess.
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Lambda-Eyde
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No - I'm not very familiar with these types of reactions. But the author of the original post barely bothered to mention moles and I found it rather
confusing, or cryptic as you said. It was not meant to be offensive, but the original post confused me because he didn't mention e.g. the number of
moles Zn needed for the nitrostyrene reduction...
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xwinorb
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I have edited the original post. Sorry, my mistake.
I would suggest also who is interested in this reduction to look at what Nicodem has posted under another post in this forum, I think the title is
"HI reductions, no red P".
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Vogelzang
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Don't they use bisulfites to reduce quinones? sodium dithionite should work, too.
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Nicodem
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Unfortunately, even though sulfites have an appropriate redox potential to perform such a reduction, they are quite nucleophilic and thus the
competitive 1,4-nucleophilic addition occurs faster, giving the 2,5-dihydroxybenzenesulfonic acid as the major product (see Journal of the
Chemical Society (1930) 2498-2502 for a study about this). The use of NaHSO3 or KHSO3 gives practically only the addition product while H2SO3
(SO2) gives some hydroquinone as well.
The reduction of quinones with sodium dithionite is the standard procedure and probably one of the most practical approaches (besides hydrogenation
over Pd-C, which is obviously the simplest and most practical). If I remember correctly, it is described in Vogel's, but you can find plenty of
examples in the primary literature as well.
…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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Vogelzang
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I've seen OTC rust removers containing sodium dithionite. I wonder how that would work.
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stoichiometric_steve
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Quote: Originally posted by turd  | | you want to reduce plain benzoquinone to hydroquinone? A weird notion to me since I always go the other direction |
I have some p-Benzoquinone which has darkened a great deal (it looks like quinhydrone) from long term storage, is there any way besides sublimation to
clean that crap up?
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xwinorb
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To Steve :
I think probably not worth doing it. Your benzoquinone is must probably OK to use. Unless you need very high purity, don't need to clean it up, that's
my opinion.
If anyway you want to make it look more nice and yellow, you might try to dissolve in minimum ammount of DCM, filter and then evaporate out the DCM
with aspirator vacuum. The benzoquinone is very soluble in DCM, I hope the impurities are not.
It works great for cleaning p-benzo made with H2SO4 and dichromate, I have posted on this.
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stoichiometric_steve
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I doubt that, pure Benzoquinone is yellow, mine is blackish!
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Sandmeyer
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It is good enough for synthetic purposes, I have never seen yellow benzoquinone and have always used black-green and it has worked.
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