Sciencemadness Discussion Board - Synthesis of 9,9‘-bianthracene from anthraquinone

Synthesis of 9,9‘-bianthracene from anthraquinone

Niklas - 2-12-2023 at 14:07

Hey everyone, just created this account, and to start I wanted to share this small experiment I carried out quite a while ago (unfortunately I didn’t take too many pictures tho, and the ones I did take honestly aren’t the best quality either..), which is the synthesis of 9,9‘-bianthracene, may be better know as 9,9‘-bianthryl to some of you, from anthraquinone, using tin granules and fuming hydrochloric acid in glacial acetic acid as the solvent, going through a Clemmensen reduction, a Pinacol coupling and an E1-elimination all in one step.

The procedure itself actually is quite straightforward, and probably something most of you wouldn’t even have to get any new reagents / equipment for, making it quite a neat compound to synthesize if you are looking for a somewhat exotic luminophor.

Required chemicals:
- 6 g of anthraquinone
- 24 g of tin granules
- 72 ml of 100% acetic acid
- 36 ml of 37% hydrochloric acid
- some 7% hydrochloric acid
- some toluene

Experimental procedure:
To a 250 ml three-neck RBF, equipped with a Dimroth condenser and a small addition funnel, all the anthraquinone and tin metal granules were added. Next all the glacial acetic acid was poured in and the solid components were brought into suspension using a magnetic stirrer.
The condenser was flushed with cold water and heating was turned on to bring the mixture to a reflux. Meanwhile the fuming hydrochloric acid was filled into the addition funnel, and as soon as things got to temperature it was added really slowly over the course of about one hour.
The reflux was continued for another four hours (a color change from yellow to olivegreen was observed within this time period), the apparatus was disassembled, and, while still hot, the reaction mixture was decanted into a beaker, leaving behind and unreacted tin.
After cooling back down to room temperature the product suspension was filtered using vacuum filtration and the resulting slightly yellow powder was washed with multiple small portions of 7% hydrochloric acid, so that residual any tin(II)-chloride, occurring as a major side product, can be removed.
After drying on the pump for a few minutes, a simple recrystallisation from hot toluene was performed, yielding some reasonably pure product that exhibits a bright blue fluorescence when irradiated with UV.
Yield: 2,93 g; 57% of the theoretical

To enable a further functionalisation of the resulting hydrocarbon a bromination using NBS in carbon tet could be performed, yielding 9,9‘-bi-(10-bromoanthracene).

I hope this small post contained some interesting information for you, would be keen to see other ones try the synthesis out too, but for now, have a good one ya‘ll!

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Fery - 3-12-2023 at 10:19

Niklas welcome here. Great experiment, beautiful fluorescence!!!

Boffis - 3-12-2023 at 15:29

Hi Niklas, welcome to the madhouse. Nice preparation and write up for this interesting compound. I wonder if you could prepare this compound by an Ullmann type reaction from 9-bromoanthracene. I ask as I have a lot of 9-bromoanthracene and no anthraquinone, I started a thread about how to utilise this compound, I envisaged de-halogenation and then oxidation to anthraquinone. I am worried that if I simply try oxidation directly on the bromo-compound I will generate brominated anthraquinones due to the liberated bromine.

On the other hand 9-bromoanthracene might just suffer the same fate as anthraquinone. Hmmm might just have to try this (thinking aloud).

Niklas - 3-12-2023 at 23:14

Quote: Originally posted by Boffis

I wonder if you could prepare this compound by an Ullmann type reaction from 9-bromoanthracene.

Would probably be another possible path, yeah. Performing the reaction in cumene under addition of thiophene-2-carboxylic acid would likely give the best results, since this way the temperature required for an Ullmann could be reached more easily.

Also thanks for the welcome!

Niklas - 3-12-2023 at 23:25

Quote: Originally posted by Boffis

I ask as I have a lot of 9-bromoanthracene and no anthraquinone, I started a thread about how to utilise this compound, I envisaged de-halogenation and then oxidation to anthraquinone.

If you still wanted to turn on into another first tho, maybe for another project, then performing the dehalogenation using sodium in t-butanol [1] and the oxidation using sodium / potassium chlorate [2] should work quite well I believe.

[1] https://patentimages.storage.googleapis.com/af/d5/67/c77d64d...
[2] https://www.chem-page.de/synthesen/anthrachinon.html?highlig...

kmno4 - 6-12-2023 at 16:44

The procedure is taken from "The Symmetrical Dianthryls. Part I" by Bell and Waring. It is attached - for the interested.

ps.
a patent (US20120065445A1) gives very similar procedure but with zinc instead of tin.

Attachment: JR9490000267.pdf (97kB)
This file has been downloaded 204 times

Boffis - 9-12-2023 at 07:56

That old JCS paper is an interesting find as it give several other routes including a Grignard reagent route but then states that the 9-bromoanthracene doesn't react with sodium even in boiling xylene! But I will still have a go at an Ullmann type reaction with copper powder and de-bromination with t-butanol and Na. Does anyone think that lithium would give 9-lithium anthracene?

@Niklas, thanks for the link to the anthraquinone prep! I must admit that I would not have thought about a chlorate in this context as I would have expected this to lead to some chloroanthraquinone side products.

Niklas - 10-12-2023 at 11:38

Quote: Originally posted by Boffis

Does anyone think that lithium would give 9-lithium anthracene?

Probably, since halogen-lithium exchanges should generally work quite well on aryl compounds like this one

Niklas - 10-12-2023 at 11:41

Quote: Originally posted by Boffis

@Niklas, thanks for the link to the anthraquinone prep! I must admit that I would not have thought about a chlorate in this context as I would have expected this to lead to some chloroanthraquinone side products.

No problem! Always like to share this synthesis approach for anthraquinone from anthracene, since it‘s much safer and also more accessible for most home chemists compared to the well known CrO3 route

Boffis - 11-12-2023 at 04:49

Yesterday I ran a "quick and dirty" experiment with 9-bromo-anthracene and copper bronze. I mixed 5.005g of bromo-anthracene with 3.001g of copper powder (an excess x2.4 molar ratio), ground them together to get an intimate mixture. A small sub-sample, circa 1g, was separated and placed in a 12mm ID pyrex test-tube and then heated in a bunsen flame until the mixture boiled freely. The molten mixture was maintained at this temperature for about 10 minutes, the mixture became dark brown and a little yellow sublimate formed higher up the tube that had to be melted down occasionally. The test-tube was cooled and then toluene was added, 1ml at a time and heated to boiling until all the solid had dissolved, 8ml were required, and filtered hot. On cooling the toluene solution deposited crystals. These were filtered off, washed with a little toluene and dried at 50 C to remove as much toluene as possible. Examination under the microscope revealed that there are 2 compounds present; sprays of non-fluorescent yellow needles, almost certainly unreacted bromo-anthracene and larger, blocky, triclinic looking, lustrous brownish tablets that fluoresce bright blue that are hopefully the dianthryl. I am going to try leaching them with various solvents to see if I can removed one of the compounds preferentially.

Today I fused the remaining portion of the mixture in a flask as before until it became almost infusible. its currently cooling down.

Does anyone have any ideas for a suitable solvent mix for TLC for these compounds?

Niklas - 11-12-2023 at 07:48

Quote: Originally posted by Boffis

Does anyone have any ideas for a suitable solvent mix for TLC for these compounds?

Something like 1:24 ethyl acetate / n-hexane should work fine I guess, at least that’s what I used for checking the purity of my 9-bromoanthracene

Niklas - 11-12-2023 at 07:52

Quote: Originally posted by Boffis

Examination under the microscope revealed that there are 2 compounds present; sprays of non-fluorescent yellow needles, almost certainly unreacted bromo-anthracene and larger, blocky, triclinic looking, lustrous brownish tablets that fluoresce bright blue that are hopefully the dianthryl.

Shouldn’t 9-bromoanthracene be fluorescent too tho?

Boffis - 12-12-2023 at 11:09

Mmm yes 9-bromoanthracene is fluorescent too. Bugger. Not as fluorescent as the dianthryl and its more soluble in isopropanol than the dianthryl.

I worked up the larger scale experiment today, just waiting for the toluene extract to crystallise.

Niklas - 12-12-2023 at 23:18

Quote: Originally posted by Boffis

On the topic of it, looking at my 9-bromoanthracene (made by the bromination of anthracene with NBS in chloroform) under the microscope I‘m noticing that there is two kinds of crystals in there too, both kinda fitting your descriptions. Oddly in my case it’s the dark crystals that aren’t fluorescent tho.. Any idea what they may be?

kmno4 - 13-12-2023 at 10:27

Quote: Originally posted by Boffis

...experiment with 9-bromo-anthracene and copper bronze....

This is very interesting, because I did not meet such Ullmann reaction, including this reactant. I would try more "standard" reaction conditions, I mean with DMF as reaction medium (hard to call it a solvent). It lowers reaction temperature, however it gives no guarantee of succsess

You may read a book "Synthesis of Biaryls" (I.Cepanec).
The only method for purification of this di(bi)anthryl I found is repeated crystallization from toluene (it forms molecular adduct 1:1 with it - just a remark to remember).

BTW.
I have ~20 g of nothing-to-do anthracene and it also gives blue fluorescence under UV, as I checked long time ago.

[Edited on 13-12-2023 by kmno4]

Boffis - 20-12-2023 at 13:02

@kmno4, do you know how stable the dianthryl-toluene adduct is? I weighed the product from my experiment mentioned above and then heated it to 70 C for 14 hours but it lost virtually no weight at all (< 1%).

kmno4 - 20-12-2023 at 15:06

I do not know, but such adducts are formed by weak forces and cannot be very stable. I think that toluene is removed below 100 C. If your product has no odour of PhMe, it is probably freed of it.
I obtained similar, crystalline adduct (unknown composition) by the way of modafinil preparation. Just crystals filteres off were very strongly toluene smelling and after standing at r.t. toluene disappeared and the crystals turn to white powder.
Info about bianthryl-toluene (and pyridine too) adduct is taken from the paper I attached (Experimental, a))
PS. during writing this post I was googling (1 minute), and TG of 9.9' bianthryl-toluene is found :

[Edited on 20-12-2023 by kmno4]