Sciencemadness Discussion Board

toluquinone reduction

xwinorb - 9-3-2010 at 19:00

The quoted text below is for making toluhydroquinone from toluquinone.

Quote:

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.


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]

xwinorb - 9-3-2010 at 21:50

I have the impression this does not work for quinones. Sorry for this post.

Lambda-Eyde - 10-3-2010 at 01:35

Are you familiar with the mole concept?

turd - 10-3-2010 at 04:52

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.

Lambda-Eyde - 10-3-2010 at 07:39

Quote: Originally posted by turd  

Have you ever done Zn/HCl or Al/Hg reductions? The metal is usually in (a large) excess.

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...

xwinorb - 10-3-2010 at 12:04

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".

Vogelzang - 10-3-2010 at 13:51

Don't they use bisulfites to reduce quinones? sodium dithionite should work, too.

Nicodem - 11-3-2010 at 06:59

Quote: Originally posted by Vogelzang  
Don't they use bisulfites to reduce quinones? sodium dithionite should work, too.

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.

Vogelzang - 11-3-2010 at 14:05

I've seen OTC rust removers containing sodium dithionite. I wonder how that would work.

stoichiometric_steve - 14-3-2010 at 12:34

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?

xwinorb - 17-3-2010 at 07:19

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.

stoichiometric_steve - 18-3-2010 at 10:15

Quote: Originally posted by xwinorb  
To Steve :
Your benzoquinone is must probably OK to use.


I doubt that, pure Benzoquinone is yellow, mine is blackish!

Sandmeyer - 18-3-2010 at 13:10

Quote: Originally posted by stoichiometric_steve  
Quote: Originally posted by xwinorb  
To Steve :
Your benzoquinone is must probably OK to use.


I doubt that, pure Benzoquinone is yellow, mine is blackish!


It is good enough for synthetic purposes, I have never seen yellow benzoquinone and have always used black-green and it has worked.