Klute - 29-4-2008 at 07:49
In the past, I have used H2O2 in IPA with catalytic amounts of I2 to oxidize hydroquinone to benzoquinone in good yields (routine >80%).
About a month ago, i translated an article on the preparation of alkylthiobenzoquinones (available in the wanted ref thread). All the hydroquinone
intermediates were oxidized with conc. FeCl3.
I have some hydrated FeCl3 i practically never use, and i would like to be able to use it for making benzoquinone, to avoid using the small amounts
of I2 needed. I have found out that benzoquinone produced with H2O2/I2 still contains appreciable amounts of I2 even after 2 recrystallizations in
IPA. Enough to permenatly taint a plastic dessicator and poision some used Pd/C drying in it anyway.
I have found virtually no information about oxidation of unsubstituted HQ with FeCl3 on the net, only a mention about it in a old scholar organic
chemistry book, by no means a preparative procedure.
I know FeCl3 produces coloured complexes with a variety of compounds, is it possible it further complexes unsubstitued benzoquinone? Or stops at
the quinhydrone stage? Has anyone got further information, or tried it out already? I guess a small scale experiment would be to bothering to try, but
i prefer asking before.
Actually, I wondering if the FeCl3 couldn't be used in semi-catalytic way, adding H2O2 gradually to reoxidize the formed Fe2+.. I would be less
bothered of using FeCl3 than I2 as a catalyst.
Thanks in advance.
EDIT: moved thread.
Bolt - 29-4-2008 at 10:07
This lab experiment may be of interest to you.
Attachment: http___bcs.whfreeman.com_expl.ntent_cat_060_experiments.pdf (85kB)
This file has been downloaded 4913 times
Klute - 29-4-2008 at 10:45
Thank you, well i suppose there wouldn't be any reason why it couldn't be used to prepare benzoquinone.. I will try a small scale experiment this
weekend.
garage chemist - 29-4-2008 at 10:50
I think woelen once said that (pure) benzoquinone stains everything with its vapors, just like iodine. So I wouldn't necessarily attribute stains in
your desiccator to iodine in your product.
Klute - 30-4-2008 at 07:27
Hum, good point. But there was definatively iodine, from the smell and purple colour. I think i remember using the same dessicator for more thoroughly
recrystallized benzoquinone before, without the same problem, at least not to that extent. I guess both compounds caused the mess.
woelen - 30-4-2008 at 08:38
Yes, pure solid benzoquinone is horrible. It has a bad smell (phenolic) and everything becomes stained with a brown color. I now store it in a triple
container, wrapped in a paper bag and guess what? The paper bag becomes somewhat brown after two years of storage. I once purchased this chemical, but
this is one of my bad purchases. I hardly used the chem for experiments, and do have a storage issue with it. But OK, it just was 25 grams and I did
not pay much for it, so the 'pain' can be overcome.
Klute - 30-4-2008 at 10:32
Indeed, it does have a rather unpleasant smell. It is pretty toxic too..
I keep it in glass bottle with a teflon cap, which works perfectly (no smell or diffusion noticed after several months of storage).
It would be nice if i could generate it insitu, or at least one pot reaction in the futur, i think small amounts of FeCl3 or I- couldn't be a big
problem when making Bunte salts.
grind - 30-4-2008 at 18:38
I think the oxidation of hydroquinone with FeCl3 does´nt give pure benzoquinone, but a 1:1 complex of hydroquinone and benzoquinone called
"quinhydrone".
Klute - 1-5-2008 at 06:25
Hum, that's what i feared in my first post... Well, i guess I'll stick to cat. amounts of I2. It isn't a big pain in itself, but it's just that i'm
running very low on I2 and would have prefered using FeCl3 rather than getting some more iodine.
I'll try a test-tube experiment though.
garage chemist - 7-3-2011 at 12:39
I made some p-benzoquinone yesterday, using a method from the Rhodium archive: oxidation of hydroquinone with sodium chlorate in 2% H2SO4 catalysed by
vanadium pentoxide.
I used:
5,5g hydroquinone
50ml 2% H2SO4
3g NaClO3
50mg ammonium metavanadate (instead of vanadium pentoxide)
Everything was mixed in a flask and magnetically stirred. Not much happened at room temperature, so I slightly warmed the mixture (ca. 30°C). This
made it turn black, and a black, foamy sludge formed. I left the reaction alone for an hour, with stirring, and as I came back, it had turned a
beautiful yellow color with plenty of finely crystalline yellow precipitate, which I filtered and washed with water.
I only pressed the substance between two filter papers to remove most of the water, and bottled the moist product to avoid sublimation losses. I am
planning to use this in Klute's synthesis of 4-methoxyphenol:
http://www.sciencemadness.org/talk/viewthread.php?tid=9835#p...
Today, I came back to the filter papers, and all the adhering benzoquinone crystals had disappeared overnight. The papers were still moist. This stuff
evaporates (sublimes) faster than water!
I find that it smells quite nice, spicy and aromatic, it reminds me of some kind of spice in chinese food.