Bromobenzene Synthesis

In this experiment, benzene undergoes electrophilic aromatic substitution with bromine. This forms bromobenzene, also known as phenyl bromide. The reaction goes forward under reflux conditions with an iron or aluminium catalyst. The product is then redistilled in order to clean it up.

Our prior videos show how to obtain bromine and benzene. We have since improved our bromine synthesis to use sulfuric acid and hydrogen peroxide.

Bromine is corrosive, toxic, and volatile. Benzene is carcinogenic and flammable. Bromobenzene is carcinogenic. Good ventilation, and skin and eye protection are essential when carrying out this experiment.

The reaction seen here is:
C6H6 + Br2 → C6H5Br + HBr

Category:

Science & Technology

Tags:

• Bromobenzene
• phenyl
• bromide
• benzene
• bromine
• iron
• aluminum
• aluminium
• brom
• benzol
• brombenzol
• bromobenzen
• electrophilic
• aromatic
• substitution
• EAS
• hydrogen
• synthesis
• organic
• chemistry
• distillation
• reflux
• cool
• chemical
• catalyst

[yellowmetalcyborg]

Nice!!

As hkparker said, a grignard reaction would be a very nice followup to this video.

I was kind of disappointed that you didn't bubble the HBr through some water to get a useful hydrobromic acid by-product.

[ReactionFactory]

@yellowmetalcyborg

Collecting HBr is a bit easier said than done! Gaseous HBr has the tendency to suck up water fairly violently, and submerging the outlet hose in a beaker of water would almost certainly lead to all of that water entering the reaction vessel itself. There is likely to be a fairly simple suckback trap that could be fashioned, but ultimately more trouble than we felt was worth it at the time.

[yellowmetalcyborg]

@ReactionFactory Yeah, NurdRage had to cope with this problem when he made muriatic acid.

I have one question, the catalyst that you used, I thought I saw tabs from coke cans, is that what you used, or did you use something else? did you have to sand off the oxide layer or anything?

[ReactionFactory]

@yellowmetalcyborg

Yes, it was an aluminium coke tab ... but this choice of catalyst is where it gets complicated. You need the bromine to react with the metal calmly and slowly, preferably when there isn't too much bromine present. If aluminium doesn't work for you, a very tiny piece of iron wool may, but our first two failures were caused by a runaway reaction when premixed reactants suddenly began reacting upon the formation of the proper catalyst.

[MrSmudger687]

@fungusmaximus1 - That's an awful lot of steps: 1) nitration of benzene 2) reduction of nitrobenzene 3) Conversion of amine to diazonium 4) Conversion to aryl bromide. 4 steps as opposed to one is going to hit the yields awfully hard, not to mention the bloody purifying of the intermediates!

[fungusmaximus1]

I think the best way is to make a diazonium salt of aniline and convert it to the aryl bromide by using copper powder and HBr. Both benzene and bromine are tough to work, even in a hood. Besides, thats way more cheaper.

[macbeth41science]

Good idea with the aluminum pop tab. The Al residue might be easier to clean up than iron. However, please get a pressure equalizing addition funnel for the side neck! An inverted funnel works well for absorbing acid fumes and won't cause suckback. The fumes must have stunk like crazy

[g3ov4n12]

You could try also to make monochlorobenzene by diazonium salt with CuCl watch?v=Bv9XVyB2Ff4 Copper chloride (I) synthesis. That would be fun.

[Chaoschemiker]

And, by the way, the unsafed valve plug scares me a little bit...

[olympicfan2]

@ReactionFactory for this problem, you can use a gas washing bottle to protect your reaction flask to get filles up with water.

[Chaoschemiker]

Really good demonstration!

The comments already mentioned some problems, you may solve the problem of HBr by simply putting some porous material (paper towels/rough cloth) drowned in an soda solution, in a vessel (e.g. a cut PE bottle) where you can lead the gas through. As PEROXOR mentioned it would be good, at least better for your yield I guess (due to controlled, slow inflow of Br2), if you inserted the bromine directly from a neck of the flask, not by filling in on the top of the condenser