p-Benzoquinone via H2O2/I2 reaction

[TheHobbit]

Ok, when one can't get p-Benzo and finds a source of hydroquinone locally and uses the H2O2/I2 synthesis to get benzo, what color should the benzo be? The iodine leaves the benzo looking red still, even after washing with IPA repeatedly. Should I keep washing or will this be good enough? I would imagine that the iodine would be rather unwanted in a wacker.

[Rhodium]

Yes, Iodine is unwanted. Recrystallize the benzoquinone from petroleum ether or toluene if it is not yellow to yellow-orange.

[GenericVersion]

is it possible to recrystal in IPA?

[bones]

umm... what about black p-benzoquinone? perhpas this explains my spectacular failure when i use benzoquinone ... twaz lab grade.... but possibly pretty old... ie mabey from the 60's

[TheHobbit]

Believe the point of using toulene/ether is to pull the I2 out of the benzo before it recrystalizes. I did manage to wash it down to a yellow-orange but I didn't know if it was suppose to be more white like they hydroquinone.

Thanks for the info though Rhodium.

[wolfx]

To bones : Your dark ( almost black ) p-benzo in fact might be quinhydrone.

[chilly_willy]

First of all this reaction can be scaled up if you are prepared to drop the flask in cool water when things start to heat up.. Also- It is well to let the reaction continue to just slightly boiling for some time. When you think you are ready to crystallize drop the whole flask in the freezer for an hour or so until you get quantitative amounts of YELLOW benzo.  Take everything over the the buchner and suction filter.. being sure to use plenty of ice cold alcohol to wash everything well.  Use saran wrap as a dam to get the last of the liquid out.  At this point your benzo should be yellow with a hint of red...canary yellow if you washed it well.  If it still has a red tint/flecks..you can recrystallize from denaturated, methanol or even water to get perfectly bright yellow crystals.  Remember as well that you can use methanol, denaturated, or isopropyl for the reaction solvent.  Afterwards put your damp Xtals in a shallow tupperware container within a larger one with CaCl..and in a few hours you will have nice large bright Xtals that dont huff and puff when you drop them in that giant 5L...