mnick12
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Preparation of 1-bromo-3-nitrobenzene
So here is a problem that I need help with. Lately I have been looking for ways to synthesize small amounts of 3-bromophenol since none of my supliers
carry it. So I was thinking of ways one could prepare small amounts starting from benzene.
My thoughts are as follows:
1. Nitrate benzene to mononitrobenzene
2. Brominate to the 1-bromo-3-nitrobenzene. Here is where I run into trouble, the nitro group is really deactivating and IIRC electrophilic
substitution occurs at a rate 10^4 times slower than regular benzene. But it is even more frustrating becuase I need that strongly deactivator to give
the desired m- product! Any ideas how I could make this reaction happen at an appreciable rate?
3. reduce the nitro to an amine
4. havent gotten this far, may be diazotization?
So please if anyone has any ideas, let me know!
thanks 10,000 times
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DJF90
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Benzene, acetylation to acetophenone, bromination occurs meta (should work alot faster than nitration), and then a Baeyer villiger (peracid) furnishes
your phenol group as the acetate.
If you're intent on starting with nitrobenzene, these two papers should provide much assistance.
[Edited on 15-2-2011 by DJF90]
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UnintentionalChaos
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Quote: Originally posted by DJF90  | | Benzene, acetylation to acetophenone, bromination occurs meta (should work alot faster than nitration), and then a Baeyer villiger (peracid) furnishes
your phenol group as the acetate. |
Baeyer-villager is not so friendly due to the peroxyacid requirement.
Hydroxylamine is rather easier to make/get. Beckmann rearrangement of the m-bromoacetophenone oxime would furnish 3-bromoacetanilide and hydrolysis,
then diazotization would give the phenol.
3-bromoacetophenone: http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5...
EDIT: I like the look of those papers! Unless you already have acetophenone, I'd go that way.
[Edited on 2-15-11 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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DJF90
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Peracid oxidation isn't too troublesome and would be a faster and cheaper route to the desired compound. m-CPBA is the typical acid used, but theres
no reason why an in situ formation of peracetic or performic acid wouldn't work. Good shout on the Beckmann though, wouldnt have thought to go round
that way.
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mnick12
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Thank you for both of those papers, they are very interesting. I am however particularly interested in the first paper which uses KBrO3 and H2SO4 as
the brominating agent. The authors theorized the brominating agent was hypobromous acid generated from the potassium bromate and sulfuric acid. My
question is could chlorate salts be used in a similair manner to chlorinate aromatics?
I hope to conduct a small scale version of this expirment some time next week, but first I will need to synthesize some more bromate.
Thanks again for the help, and if things work out well I might put up some pictures.
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mnick12
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A little update.
I ran the synthesis of nitrobenzene found on Vogel, but instead of a steam bath I used mag stirring @ 1200rpm which seemed work well (really
exothermic reaction). I washed the crude nitrobenzene twice with water once with a 10% KOH solution once more with water then dried with MgSO4. Next I
did a vacuum distillation and the nitrobenzene passed as a pale yellow oil @ 123 degrees. Not sure what the yield is but it looks pretty good.
Anyway I still dont have any potassium bromate yet, I need a new power supply so I can make some more. Stay tuned!
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mnick12
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Good news, and sorry for the triple post.
Anyway I did a small scale run of the procedure described in "Bromination of Deactivated Aromatics Using
Potassium Bromate", and it worked very nicely. The yields were not as good as the authors claim, but I suspect it is because I did it on 1/100th
scale. Thanks for the paper DJF90.
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DJF90
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No problems. Any chance of an experimental write-up/pictures?
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Jor
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I did the synthesis of bromobenzene via the paper you posted.
To 66mL of water was added 33g of conc. H2SO4. Mext 7,8g of benzene was added, followed by 16,7g of potassium bromate. The mixture obtained a slight
orange color. It was stirred overnight at RT, some KBrO3 did not dissolve.
After 1 night of stirring I took the benzene layer and measured it's density. It was almost 0,90 g/mL indicating only a slight conversion.
The only reason I see for the very slight conversion is that I did not stir vigorously enough. This seems essential, because you have 2 phases. I want
to continue the reaction for more days, but I have to leave for 3 weeks tomorrow, so I decided to dispose of the mixture (a waste I know  , should have done smaller scale). I took the benzene layer to organic waste and boiled
the solution to remove dissolved benzene. This resulted in a sudden huge release of bromine as a vapour, wich was formed at a certain temperature  . Fortunately it was no match for my hood.
I will try again later with different conditions.
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DJF90
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Jor, how was you stirring your reaction? Magnetic stirring?
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Jor
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Yes, but I only used a small one because my large stirbar was used in another reaction.
Further more, I couldn't put it on a very high speed, as sometimes my stirrer tends to go 'out of control', meaning it will jump around in the flask.
Therefore I could only let it stir slowly overnight.
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mnick12
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I wont be able to do any lab stuff for about 2 months , but I will tell some
things I did which may be usefull for your efforts.
Prior to me actually attempting the procedure I did some proof of concept runs just to see if there was anything happening at all. Anyway what I
noticed was when all the reagents are mixed ( H2SO4, KBrO3, nitrobenzene, water) the mix heats up and there is the evolution of some gas along with
some Br2, but other than that nothing happens. However if you stirr it vigorously ( mine was at 1400rpm) after some time the mix will get very hot,
then as it cools the compound (in my case 1-bromo-3-nitrobenzene) precipitates out as fine yellow crystals.
Anyways thats all for now, if you have any questions let me know as I would be happy to help. However it may take me a few days to respond.
good luck!
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