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Author Topic: Synthesis of 1,2,3-tribromobenzene  (Read 24829 times)

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aleksxxx

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Synthesis of 1,2,3-tribromobenzene
« on: April 27, 2007, 09:10:38 AM »

Okay -

I have to synthesize 1,2,3-tribromo benzene for a study questions starting w/ benzene and using any needed reagents.

I am pretty lost - the only way i can think to do this is the following (but i dont think it will work becuase the groups are deactivators)

1. Make aniline
2. React that W/ Br2 and seperate out the ortho, leaving a Br para to NH2
3. Oxidize the NH2 to a Nitro group again, leaving a NO2 and Br para
4. I would brominate here, since the Br would direct ortho and the NO2 would direct meta (This is where i dont think it would work because the Br and NO2 are both deactivating, so i dont know if the rxn would proceed), if it did go, it would leave my required product only w/ a nitro group i would have to remove.

Please let me know if that route has any shot to get any product, or any tips on how to get there.
Much appreciated.
« Last Edit: April 27, 2007, 11:12:51 AM by aleksxxx »
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refid

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aleksxxx

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #2 on: April 27, 2007, 05:05:13 PM »

Heres what i think...

http://bp1.blogger.com/_60ljWjzZHA0/RjK4yBDZJUI/AAAAAAAAAWc/Vszfmw6anWU/s1600-h/triBromo-ben.JPG

what do guy think

ahhh
that looks good.. way better than what i came up with!
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refid

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #3 on: April 27, 2007, 05:08:01 PM »

Br and NO2 are both deactivating,


Br is a deactivator but ortho/para director

I think your way is possible... u can get rid of the nitro group by deamination by diazotation
« Last Edit: April 27, 2007, 05:14:18 PM by refid »
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aleksxxx

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #4 on: April 28, 2007, 03:19:20 AM »

Br and NO2 are both deactivating,


Br is a deactivator but ortho/para director

I think your way is possible... u can get rid of the nitro group by deamination by diazotation

thats how i was planning on it, but since the Br and NO2 are both deactivators (even though directing where i want the bromines to go) i didnt think it had a shot in reacting.
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refid

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aleksxxx

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #6 on: April 29, 2007, 09:53:48 AM »

here is a way i thought about today... lemme know..

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english

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #7 on: April 29, 2007, 10:06:34 AM »

That substitution reaction with PBr3 won't work. Aryl compounds do not readily undergo substitution reactions unless you have a decently strong deactivator.

You may have difficulties using Br as a deactivator.


I don't see why you can't just use three equivalents of Br2 and FeBr3.
You'll obviously get para-directing side reactions, but this method seems considerably easier. 
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aleksxxx

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #8 on: April 29, 2007, 10:14:20 AM »

ok, so just brominating benzene w/ 3 equiv. would work you think?  Wouldnt para be preferred to ortho becuase of steric hinderance leaving you w/ 2 bromines para and then some ortho?
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english

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #9 on: April 29, 2007, 10:33:44 AM »

ok, so just brominating benzene w/ 3 equiv. would work you think?  Wouldnt para be preferred to ortho becuase of steric hinderance leaving you w/ 2 bromines para and then some ortho?

Such a compound is bound to be quite hindered.  Making hindered molecules usually entails lower yields.

I'm sure there's some genius alternate process of which I'm unaware.  You have two choices though.  Your inital, really long and complicated process, or mine, which takes 3 steps.   :P

If it's not a matter of yield and only how to get to the product, then don't worry about the complications, just the path that takes you to the end.
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aleksxxx

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #10 on: April 29, 2007, 10:36:32 AM »

ok, so just brominating benzene w/ 3 equiv. would work you think?  Wouldnt para be preferred to ortho becuase of steric hinderance leaving you w/ 2 bromines para and then some ortho?

Such a compound is bound to be quite hindered.  Making hindered molecules usually entails lower yields.

I'm sure there's some genius alternate process of which I'm unaware.  You have two choices though.  Your inital, really long and complicated process, or mine, which takes 3 steps.   :P

If it's not a matter of yield and only how to get to the product, then don't worry about the complications, just the path that takes you to the end.

ok sounds good...

would i still have to block the para position w/ somehting though?
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english

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #11 on: April 29, 2007, 10:39:57 AM »

would i still have to block the para position w/ somehting though?
I don't know of a cleaving reaction that would rid you of your blocker afterwards.
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refid

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #12 on: April 29, 2007, 10:43:03 AM »

would sulphonation work in this case? also once the first Br is added to the othro postion wouldnt it direct ortho/para relative to it self?

english

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #13 on: April 29, 2007, 10:45:41 AM »

also once the first Br is added to the othro postion wouldnt it direct ortho/para relative to it self?

That's the idea, yes.
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refid

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Re: Synthesis of 1,2,3-tribromobenzene
« Reply #14 on: April 29, 2007, 10:49:24 AM »

so your hoping by chance, they'll direct ortho 
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