October 15, 2019, 07:25:28 AM
Forum Rules: Read This Before Posting


Topic: 2-bromo-6-nitrophenol problems in synthesis and IR  (Read 5654 times)

0 Members and 1 Guest are viewing this topic.

Offline latent_lamp

  • Regular Member
  • ***
  • Posts: 12
  • Mole Snacks: +0/-0
  • Gender: Male
2-bromo-6-nitrophenol problems in synthesis and IR
« on: June 10, 2006, 01:39:32 AM »
Background:
Well I tried brominating o-nitrophenol with just liquid bromine and acetic acid. I heated the solution, filtered, washed with H2O and finally recrsytallized with ethanol.

The M.P initially of o-nitrophenol was 45ish and the final product had 66-67 C. The reactant was actually an unknown compound that I had to identify spectroscopically and either derive brominated product or benzoate. I obviously chose the easier one :)

So the reaction was 2-nitrophenol + Br2 (liquid) ---> 2-bromo-6-nitrophenol

Problems:

Vogel had the derivative down as a dibrominated compound 2,4-dibromo-6-nitrophenol. I got 2-bromo-6-nitrophenol. March's explained that Bromination of a phenol would lead to ortho being preferable. I might have read it wrong but my product exclusively was a brominated substituent that was ortho to the hydroxyl (i.e. the 2-bromo-6-nitrophenol).

I would have thought that the said product would be a minor simply due to steric hindrance (the Br is huge as hell, it would probably be more hindered next to OH than a simple H in para confirmation).
So I beg to ask the question, why did I get ortho instead of para?


Problem 2:

I tried ACS, RCA, Science-direct, SDBS and loads to textbooks, I cannot find IR for 2-bromo-6-nitrophenol anywhere to compare it with my IR. I particularly need help here.


Now the expected product from Vogels would never have occured in the conditions I did my experiment in. The ring would have been far too deactivated for a second bromination to occur, especially in the relatively mild conditions I did it in.



Many Thanks,
a very lazy chemist.
The world is my oyster, but I am a vegetarian.

Offline wereworm73

  • Chemist
  • Full Member
  • *
  • Posts: 179
  • Mole Snacks: +21/-4
Re: 2-bromo-6-nitrophenol problems in synthesis and IR
« Reply #1 on: June 11, 2006, 08:38:35 PM »
That's weird.  Did you get any 4-bromo-6-nitrophenol at all?  I would think you'd at least get some of it because there's little steric hindrance and the bromine is both meta to the deactiving nitro group and para to the activating hydroxyl group...

Maybe the hydrogen comes off easier from 2-bromo-6-nitrophenol because it's closer to the pi-bond between the OH and the aromatic ring? 


Offline chiralic

  • Full Member
  • ****
  • Posts: 234
  • Mole Snacks: +19/-3
  • Gender: Male
  • Test
Re: 2-bromo-6-nitrophenol problems in synthesis and IR
« Reply #2 on: June 11, 2006, 09:04:24 PM »
Could you post your IR Spectra?

Suppose that you had obtained 2-bromo-6-nitrophenol, Did you see band of OH (Broad band on 3500-3000), Br(below to 667 is hard to see on Normal IR and NO2 (Strong bands on ~1550-1330)?

Regards,

Chiralic


Offline latent_lamp

  • Regular Member
  • ***
  • Posts: 12
  • Mole Snacks: +0/-0
  • Gender: Male
Re: 2-bromo-6-nitrophenol problems in synthesis and IR
« Reply #3 on: June 12, 2006, 01:56:29 AM »
Could you post your IR Spectra?

Suppose that you had obtained 2-bromo-6-nitrophenol, Did you see band of OH (Broad band on 3500-3000), Br(below to 667 is hard to see on Normal IR and NO2 (Strong bands on ~1550-1330)?

Regards,

Chiralic




IR was exactly as you mention but Br was around 678. Also I did not get any of the 4-bromo-6nitophenol. Coz it would have crystallized with ethanol as solvent. It sucks, I swear. I know the 2-bromo product has lots of steric hindrance, thats why I cant explain why its so favourable....waaaaa
The world is my oyster, but I am a vegetarian.

Offline latent_lamp

  • Regular Member
  • ***
  • Posts: 12
  • Mole Snacks: +0/-0
  • Gender: Male
Re: 2-bromo-6-nitrophenol problems in synthesis and IR
« Reply #4 on: June 15, 2006, 10:47:19 AM »
could the 2-bromo-6-nitrophenol be kinetically preferred? I mean it is possible for it to require less activation energy than 4-bromo-6-nitrophenol?
The world is my oyster, but I am a vegetarian.

Sponsored Links