Tapajos
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Synthesis of Triptycene from bromobenzene
Most of this synthesis is oriented to getting to benzyne which may seem like a fairly easy to synthesize chemical but it really isn't. Benzyne is
extremely unstable and will decompose in a quick manner. There are two main routes to generating it in situ.
One is the diazotation of anthranilic acid. The second one I will be doing is the grignard reaction of 2-fluorobrombenzene.
To get there I will need 2-nitrobromobenzene which will get reduced to the corresponding aniline and that aniline will undergo a Balz-Schiemann
reaction which is basically a sandmeyer but for Fluorine. Usual acids used are Hexafluorophosphate and Tetrafluoroborate.
Now to get to the Nitrobromobenzenes.
I used the Nitration of bromobenzene since I don’t have nitrobenzene.
A large problem with this synthesis is the isomer selectivity. It mainly forms the para isomer. The ortho one is the only one which will work. Another
issue is purifying them. Usually you would steam distill the isomer mixture (~1% meta isomer) and seperate para from ortho but that doesn't work so
fractional crystallisation will be used.
A user sent me this german paper( https://doi.org/10.1002/cber.189602901142 )which tremendously helped me to find the right solvent.
It says the para isomer is very soluble in ethanol at rt. But with a bit of water added its not very soluble and most crashes out but the ortho keeps
being soluble and it is slowly percipitating out of the mother liquor.
https://imgur.com/TzL0BKR
I added the product to a Sn/HCl reduction
(at the point where i am writing this it is 4 months past the experiments and i lost my old lab notebook so i have no idea what the yield here was)
https://imgur.com/oIAYE3D
The mixture was poured into a volume of water and sodium hydroxide was added to percipitate the tin and freebase the aniline, DCM was added and
gravity filtration was done over the night (It was very cold so minimal DCM was lost surprisingly). A distillation of the solvent was performed and
when no more liquid came over Hydrochloric acid was added to the resulting colorless oil giving this mass of 2-bromoaniline Hydrochloride.
https://imgur.com/tPhkDZJ
https://imgur.com/WqXeHHr
Here the yield decreased rapidly as you might tell visually so I stopped here. Doing a Balz Schiemann with these amounts will virtually not be worth
with my equipment since I do not have small jointed short path apparatuses.
[Edited on 11-7-2025 by Tapajos]
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Tapajos
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the images will not load wait 
Learn to embrace the tar
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Fery
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Hi Tapajos and welcome on the forum!
You did nice experiments and thanks for sharing.
The images are visible after clicking their links.
You wrote that you do not have nitrobenzene. That does not hurt because its bromination gives predominantly 3-nitrobromobenzene and you need 2-
The route to benzyne by diazotization of anthranilic acid - there is a risk of an explosion
https://sci-hub.st/10.1021/ed045p272
Attachment: 10.1021@ed045p272.pdf (912kB)
This file has been downloaded 84 times
You do not have anthranilic acid. Methyl anthranilate is widespread flavoring agent. Anthranilic acid is watched substance but trivial to obtain by a
hydrolysis of its ester. It is sold on ebay in amounts like 300 g, 500 g, 1 gallon
https://www.ebay.com/itm/203101086335
https://www.ebay.com/itm/236150541088
https://www.ebay.com/itm/387877107548
You are at opposite side of the Earth but in EU you can buy the ester at price 78 EUR per 1 liter
https://shop.es-drei.de/ester/11927/anthranilsaeuremethylest...
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Texium
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Thread Moved
12-7-2025 at 09:58 |
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