Boffis
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9-Bromo-anthracene
In amongst a batch of chemicals I acquired not long back was a considerable quantity of a compound called 9-Bromo-anthracene. Does anyone know what it
could be used for? The fact that one lab had no less than three, originally 500g, jars of the stuff suggests that at one time it had some very
important use.
I have done quite a bit of research on this material and it appears that it can be converted to a Grignard reagent (with some difficulty according to
a JACS article) and then to all the usual products of Grignard reactions. There is an extensive body of information in the older text (mostly German)
on the Halo anthracene but strangely there is very little information on the 9-monobromo derivative. It appears that it is easily brominated further
in chloroform, carbon tetrachloride. or acetic acid to 9,10,x and 9,10,x,x tri and tetrahalo anthracenes and anthracene halides (ie halogen addition
products without the lost of hydrogen halide). When these compounds are treated with hydroxides they are converted into various halo-anthracenes or
halo-anthraquinones depending on the number and position of the halogens added per molecule of anthracene.
9,10-dihaloanthracene are easily oxidised, apparently to anthraquinone, and reduced with Zn to anthracene.
Anyone got any more ideas?
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Texium
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I was curious, so I did a Sci-Finder search. It looks like there are over 2,000 published reactions using 9-bromoanthracene. On a cursory look, it
seems like most use it as an exemplary bulky aryl halide for testing new cross-coupling conditions, but there are a few unique things in there. Take a
look here: https://www.sciencemadness.org/whisper/viewthread.php?tid=28...
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numos
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I think metalation followed by nucleophilic addition or cross coupling are going to be the main modes of reactivity.
I think cross coupling reactions are not great for home chemistry, but you might attempt an Ullmann coupling. These can be done with only a copper
catalyst and give the homocoupled product. Not useful on its own, but kind of a neat case of axial chirality akin to the binol class of compounds.
Might make for some neat ligands if you can functionalize the bromoanthracene first!
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Texium
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After running a number of cross-couplings in my university lab, I’ve realized that they aren’t always as intimidating and sensitive as I
previously expected. If you have triphenylphosphine, palladium chloride, and a means of blanketing your reaction with an inert gas, you’re in good
shape. Once I have time to get back into amateur chemistry, I intend to demonstrate the feasibility of running Suzuki couplings in a home lab.
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numos
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Cross couplings are easy to run - true, they are the archetype of a dump and stir reaction.
The problem is that unless you are following a literature procedure and the yield is very high, isolation and purification tends to be challenging.
For challenging substrates, you might get several products, and I'm not saying it can't be done, but the few times I've attempted sonogashira
reactions at home I would get less than 50% conversion, and there would usually be some amount of homocoupled by-products. Really the only way to
separate these mixtures are with column chromatography.
I agree that for simple substrates that crystalize selectively or where you can use solubility to your advantage, it's doable. But, bromoanthrancene
is highly crystalline and its byproducts and products are likely similarly soluble, so crystallization likely will not give you clean product.
That being said, there are certainly high yielding and clean coupling reactions out there, so while I still think it's not great for home chemistry,
prove me wrong and you'll make a big splash in the home-chem community! 
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mackolol
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If you really are able to convert in into some anthraquinone derivative, you can make some substituted diphenylanthracene from that as a dye for glow
stick reaction.
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Boffis
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Whoo Texium, thankyou for the search results, its going to take me a while to work through these but some of them look doable. I am also going to try
the OrgSynth preparation of 9,10-dibromoanthracene but start with the mono bromo compound instead of crude anthracene and use less bromine.
I am also thinking of trying to dehalogenate it to pure anthracene. I haven't decided on the method but this has been discussed under the
dehalogenation of halobenzenes on numerous occasions on this forum, I let you know how I get on.
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Boffis
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Finally got round to doing some practical experiments on this substrate! I am working on an extended article with photos for the prepublication
section.
Oxidation of 9-Bromoanthracene to anthraquinone
A brief note in von Richter's "Chemistry of Organic Compounds" under the description of 9,10-dichloroanthracene states that when this compound is
oxidised it yields anthraquinone with the loss of its chlorine. This raised the possibility that oxidation of 9-bromoanthraquinone would similarly
yield anthraquinone. The following preliminary experiment was based on the experimental procedure for the oxidation of anthracene to anthraquinone
presented in Cain and Thorpe(1).
14.401g of 9-Bromoanthracene was dissolved in 100ml of boiling glacial acetic acid under a reflux condenser in a 500ml flask equipped with a magnetic
stir-bar. The chromic acid oxidising solution was prepared by dissolving 20.0g of chromium trioxide in 15ml of water and then diluting with 75ml of
glacial acetic acid. The chromic acid solution was added slowly from a dropping funnel through the reflux condenser and such a rate as to maintain a
steady reflux. After the addition of about 35-40ml of the chromic acid solution the separation of anthraquinone requires additional external heat to
be applied to maintain a vigorous reflux or the reaction mixture becomes hard to stir. Once most of the chromic acid solution had been added much
bromine vapour began to reflux. Addition took about 40 minutes. When all of the chromic acid solution had been added the dark green solution was
cooled a little until reflux ceased and then the condenser rearranged for simple distillation into a vented receiver, the vent having a pipe to an
inverted funnel in a beaker of dilute sodium hydroxide to absorb bromine and other vapours. The bromine was then distilled off until the distilled
vapour was practically colourless acetic acid, about 20ml were distilled off. The contents of the flask were cooled a little and then poured into
400ml of cold water and a further 100ml of water used to rinse the flask. The diluted suspension was allowed to cool to room temperature (c 10°C) and
filtered. The pale-yellow solid was washed repeatedly on the filter until the washings were neutral and clear. The cake was dried at 40-45°C for 14
hours to give 11.319g of crude anthraquinone, about 97% of theory.
Comments
This procedure was adapted from an experiment to oxidise an equivalent molar quantity of anthracene (10.0g) and if anthracene is used the bromine
distillation may be dispensed with. An attempt was made to recover the chromium from the residue without first neutralising the large amount of acetic
acid by the addition a large amount of potassium sulphate with the intension of causing the crystallisation of chrome alum but this did not work. Even
after evaporation to about 300ml only a green basic chrome salt or hydroxide precipitated.
The bromine distillate was neutralised with a mixture of sodium hydroxide and sodium sulphite then discarded. In a larger scale preparation, it may be
possible to utilise the bromine-acetic acid mixture for something as this is a common brominating mixture.
(1) Book: The Synthetic dyestuffs and intermediate products, J.C. Cain and J.F. Thorpe, 7th edition, [1933], page 349. (Or Practical Organic
Chemistry, Cohen, [1926], p287 (also in downloadable 1910 edition) from which Cain and Thorpe credit taking the preparation.)
Hey Mods, do you think you coud move this thread to the Organics section?
[Edited on 2-1-2024 by Boffis]
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Texium
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Thread Moved
17-1-2024 at 06:31 |
Boffis
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I recently ran a larger scale experiment on the oxidation of 9-bromoanthracene directly to anthraquinone. 28.835g of bromoanthracene were oxidised to
give 22.186g of final product, a yield of 95%. The product appears to be free of bromine using the flame test and is a pale yellow crystalline solid,
much paler in colour than the anthraquinone prepared from crude anthracene. I will post the full details in the pre-bublication section.
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