Cyanocobalamin - 2-3-2012 at 19:10
I wanted to synthesize quinone, and unfortunately I ran out of hydrogen peroxide and iodine, so I thought persulfate would as well do the work
So when I added persulfate solution to a hydroquinone solution (both aqueous), the solution turns from colorless to yellow, then to a dark red
solution, meanwhile some dark (almost black) needle-like crystals with metallic lusture crystalize out, and they got so much that it filled the whole
beaker...
Anyone have any idea about what is this? 
mnick12 - 2-3-2012 at 19:36
It is most likely quinhydrone which is a complex of hydroquinone and benzoquinone. It is often the product of an incomplete oxidation, so either you
need more oxidant or your persulfate is inadequate in this application. From my own experience sodium and potassium chlorate are effective as an
oxidant.
Cyanocobalamin - 2-3-2012 at 19:42
oh thanks! I have potassium chlorate, but org syn said that it needs vanadium pentoxide which I don't have ...
but I still don't understand...because hydroquinone is colorless in solution and quinone is yellow in color, how come I would get such dark solution
and crystals?
I searched the internet and I found Elbs persulfate oxidation of phenol, could it be something analogous to this happened? but the resonance of the
negative charge goes to an ortho-position?
I will try to post some images here later
Cyanocobalamin - 2-3-2012 at 23:36
Would it be possible that the solid is tetrahydroxy-1,4-benzoquinone?? The description in wiki is very similar to what I have observed: red solution
with glistening dark solid
http://en.m.wikipedia.org/wiki/Tetrahydroxy-1,4-benzoquinone
Nicodem - 3-3-2012 at 02:35
Why do you have this need to pull out the most unlikely and absurd explanations? Mnick12 already gave you the most reasonable explanation. You did the
reaction in water so it is highly unlikely it could go all the way to 1,4-benzoquinone. It is most likely the major product under such conditions is
quinhydrone which precipitates out due to lower solubility. Quinhydrone does not oxidize as readily as hydroquinone and it would take a long time to
oxidize it to 1,4-benzoquinone under such heterogeneous conditions.
PS: Please open referenceless topics only in the Beginnings section.
Cyanocobalamin - 3-3-2012 at 04:49
Oh I see~ Thank you 
woelen - 4-3-2012 at 23:48
What happens in this reaction is the formation of a complex, as others stated. Only half of your hydroquinone is oxidized to quinone. You need more
oxidizer to get the other half oxidized, but this is harder, because the hydroquinone now is in solid form as part of the quinhydrone-complex.
A very educational experiment would be to add a solution of quinone (yellow) to a solution of hydroquinone (colorless). When these solutions are
mixed, the liquid becomes very dark and soon thin needle-like crystals form, which make up a weird network of crystals, filling up the entire volume
of liquid. This network is very fragile though and simple stirring breaks it up.
C6H4(OH)2 + C6H4O2 --> C6H4(OH)2.C6H4O2
The latter is quinhydrone, a 1 : 1 adduct of hydroquinone and quinone.