hydroquinol --> quinhydrone

[PolytheneSam]

From CA Vol. 3 page 2698

Oxidation of Hydroquinol by the Catalysis of Carbon. MOTOOKI MATSUI. Mem. Col. Sci. Eng., Kyoto, I, 386-90. -- When dissolved in H₂O, alc., or Et₂O, hydroquinol is oxidized to quinhydrone, in presence of air and a little animal charcoal, at the ordinary temp.  The reaction proceeds more quickly when the sols. are boiled.  Finely divided wood charcoal acts in a similar manner but less energetically.  J. B. T.

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Hydroquinol is a synonym of hydroquinone according to the Merck Index 9th edition.  Quinhydrone is an addition compound of one mole of hydroquinone and one mole quinone (Merck Index 9th edition).  Maybe dilute NaOH could be used to seperate the hydroquinone from the quinone.

[Vitus_Verdegast]

Nice find, i suppose it could easily be oxidized in the same pot.

[PolytheneSam]

Looks like it could also be applied to this.

Post 313044

(Mountain_Girl: "Substitute quinhydrone for benzoquinone ?", Chemistry Discourse)

[Mountain_Girl]

Nice one, Sam.

The reaction proceeds more quickly when the sols. are boiled.

My own experience of recrystallizing quinhydrone using hot water is that as the bp is approached it seems to decompose. Maybe due to a combination of excess temperature and some remaining oxidant in the solution. Or maybe I'm imagining things...dunno
[better to use ~ 50% aqueous MeOH for recrystallizing & not let it get too hot]
Therefore, I would only boil the reacting solution if it were Et₂O or maybe MeOH but not something with a higher bp.

Also quinhydrone seems to be considerably less soluble in water than hydroquinone, so I suspect the stuff would just precipitate out of solution. So chilling and filtration will recover most of the product (along with the charcoal but that can be dealt with).
This is based on my own experience of what happens when I prepare quinhydrone from hydroquinone using FeCl₃ or using I₂/H₂O₂, both of which are supposed to give benzoquinone, but for some reason don't  

Fortunately, quinhydrone can definitely be substituted for benzoquinone in the synth of p-MeO phenol from hydroquinone.

[PolytheneSam]

Here's an interesting patent:

Patent DE3207937

A method of production of 4-alkoxyphenols by reacting hydroquinone with an alcohol at a high temperature and in the presence of benzoquinone and perchloric acid.

Here's a translation of the example (Beispiel)

55 g hydroquinone and 11.5 g 70 % perchloric acid are dissolved in 300 ml of ethanol, then 8.6 g p-benzoquinone is added and (the mixture is) heated under agitation (ie. stirring) to reflux.  The reaction mixture is held at reflux temperature for 2 hours, thereafter the batch is concentrated (ie. evaporated) and taken up in 200 ml ethyl acetate and 100 ml water.  After seperation of the aqueous phase the organic phase is washed with water and dilute NaHCO3 solution.  After removing the solvent medium one obtains 56.1 g (81.2 % Theoretical) 4-ethoxyphenol, Kp 115-119°/0.8 kPa.*

*Kp is probably Kochpunkt (boiling point)
kPa looks like kilopascals