My Synthesis of 3-Bromobenzonitrile

Introduction
I made some 3-bromobenzonitrile they other day, and wanted to share the writeup with y'all.


Synthesis
I couldn't find a procedure for the synthesis of 3-Bromobenzonitrile by bromination, so I did a similar one to the bromination of benzene.


The reaction.

I started by adding 5,76 g (0,055 moles) benzonitrile to a three-necked round bottom flask. I also added a few pieces of steel wool.

I equipped the flask with an addition funnel, water-cooled condenser and a glass stopper.

I added 8,8 g (0,055 moles) bromine to the addition funnel, and slowly opened it.

Once a few milliliters of bromine were added I stopped the addition and started heating the flask. When red-cloudy vapours (at around 70 C) were visible I continued the heating and resumed the addition of bromine.


The flask containing steel wool, bromine and benzonitrile.

After around 1/4 of the bromine was added it no longer gave off red cloudy vapours, and there was no more steel wool left. I therefore added a bit more steel wool and continued the addition of bromine.

NOTE: If the bromine was added too quickly it started to bumb. The reaction also seems to be exothermic, but since I was also heating, it is hard to say.

When all the bromine was added, and the steel wool was used up, the mixture stopped giving off red-cloudy vapours. I let the mixture cool, added water and extracted the product 3 times with around 100 mL of ethyl acetate.

I evaporated off the ethyl acetate to a white powder smelling strongly of bitter almonds.

The product seems to melt around 30-40 C, but I will do a more precise test later.

The yield was really low (around 20%). I think this is because I did not know it's solubility, and I therefore tried multiple solvents. Some it was soluble in, but also extracted impurities. Ethyl acetate seems like the best one.


The CRUDE product (still wet and not recrystallized).

Notes
The reason for extracting with ethyl acetate was that I made the mistake of adding water to the mixture, not being able to seperate it, and then adding sodium hydroxide solution. Some iron compound started precipetating, Fe(OH)3?, and assuming the 3-bromobenzonitrile also precipetated, I did not know what to do besides extracting it. I could probably have been a bit more wise, but oh well

[Edited on 11-5-2025 by Maui3]

[Edited on 11-5-2025 by Maui3]

Interesting (classic) reaction in an amateur environment. I'd rather read more about your actual experiences with this reaction (how long did it take to add all the bromine, how long till the red fumes dissipated in the flask, reaction temperature, even if it was just an estimate, the extraction details (how much EtOAc used, how many times you actually extracted the water phase), the yield, tlc purity, etc than reading about your intented use of the product!

On the "political" side of things: why on earth "need" anyone know what you want to use this compound for, especially if it is the first (or second, at best) step in a multistep reaction? Chemistry is like LEGO, one can combine the blocks many absolutely harmless ways but no, you had to take a shady one... We are not your superiors here, you don't have to explain your intentions and actions to anyone. But if you were reckless enough to do so then bear the consequences!

Anyway, what if you revised your synthesis description and added more chemically relevant details and removed the irrelevant "ramblings"? Again, this bromination is a nice "old school" reaction in itself, the product with almond scent is also interesting! I'd like to read more about these kind of things! Do you really need that extra "ego boost" that comes with the explanaton of planned use? Yeah, you are a "though" one, everyone can see that! Now feel better?

Thank you for the suggestions Pumukli!

I edited the post to include how long it took to add all the bromine, how long until the red fumes dissipated, the reaction temperature, how much ethyl acetate was added and how many times the water phase was extracted. AND MOST IMPORTANTLY: Not what I am going to synthesize with it.

Yeah - I get what you mean about me saying what I was going to use it for. I thought someone might get an idea, since it's a relatively niche building block - and I therefore just wanted to acknowledge that I was not a clandestine meth cook xd. I do not need an extra "ego boost", just thought it would be better to note.. but I was doubting it too.

Anyway, I am happy you liked the post (without the "ramblings").

What do you think now? Is the post better