[levis123]

I tried the bromination of isophthaldehyde with NBS in sulfuric acid. Did an extraction and evaporated the solvent, the TLC of the crude product showed 5 spots, one of which was SM, slightly above that - I thought - was my product, the rest I assumed were due to side reactions involving radicals.

So I did a column to separate the spot with the highest intensity, assuming it was 5-bromoisophthaldehyde. However, the H NMR spectrum does not add up. It shows two singlets at 10.45 and 10.40 with relative integrations 2:1. How is that possible if the compound is symmetrical? If it is not what I assume it is, and the bromination has taken place somewhere else (giving a non-symmetrical molecule), shouldn't the integrations be 1:1 (for two aldehyde protons)? The TLC of the final compound shows only one spot so I know it is pure...

Any ideas?

[kriggy]

The protons ortho to the bromine give you the integral for 2 while the one between carbonyls give you the integral for 1

[levis123]

The protons ortho to the bromine give you the integral for 2 while the one between carbonyls give you the integral for 1

Sorry maybe I wasn't clear enough, I only mentioned part of the spectrum, assuming that those peaks correspond to aldehyde protons. Full spectrum: 10.45 (s, 2H), 10.40 (s, 1H), 8.36 (d, 1H), 8.29 (d, 1H), 8.21 (s, 2H).

[OrganicDan96]

Sorry maybe I wasn't clear enough, I only mentioned part of the spectrum, assuming that those peaks correspond to aldehyde protons. Full spectrum: 10.45 (s, 2H), 10.40 (s, 1H), 8.36 (d, 1H), 8.29 (d, 1H), 8.21 (s, 2H).

looks like you have too many aromatic protons

[levis123]

Sorry maybe I wasn't clear enough, I only mentioned part of the spectrum, assuming that those peaks correspond to aldehyde protons. Full spectrum: 10.45 (s, 2H), 10.40 (s, 1H), 8.36 (d, 1H), 8.29 (d, 1H), 8.21 (s, 2H).

looks like you have too many aromatic protons

Oops I also forgot a peak at 10.01 (s, 1H), which I think is the one between the two aldehydes..

[levis123]

Sorry maybe I wasn't clear enough, I only mentioned part of the spectrum, assuming that those peaks correspond to aldehyde protons. Full spectrum: 10.45 (s, 2H), 10.40 (s, 1H), 8.36 (d, 1H), 8.29 (d, 1H), 8.21 (s, 2H).

looks like you have too many aromatic protons

Yes, but I cannot understand what is really happening. Is the compound not pure? Do I have a mixture? Or did some other reaction occur instead of the bromination?

[Babcock_Hall]

Are you following a literature protocol that is specific for isophthaladehye?  Speaking in very general terms for a moment, I would say that aldehydes can undergo addition or oxidation reactions.

[levis123]

Are you following a literature protocol that is specific for isophthaladehye?  Speaking in very general terms for a moment, I would say that aldehydes can undergo addition or oxidation reactions.

Yes I am following an exact literature procedure for isophthaldehyde, and the spectrum of my product does not match theirs. The NBS I used was not recrystallized, perhaps that could be an issue?

[rolnor]

NBS is not so sensitive should be OK. Do you run TLC during the reaction?

[levis123]

NBS is not so sensitive should be OK. Do you run TLC during the reaction?

No, the reaction solvent is concentrated sulfuric acid and I thought that would mess up the TLC. Perhaps I could have done a mini workup before running a TLC, but I thought it was going to be a clean reaction anyway so I decided not to do it.

[OrganicDan96]

i think you probably have a mixture by the fact that you have several aldehyde signals. have you got an NMR of your stating material?

[levis123]

i think you probably have a mixture by the fact that you have several aldehyde signals. have you got an NMR of your stating material?

No, that is the next thing I will do. However, a mixture is unlikely. When I ran a TLC of the crude material, on which I also spotted the aldehyde starting material, I saw that I had a mixture, as one of the spots matched the Rf value of the SM. After the column chromatography, I ran another TLC which only showed one spot.

[rolnor]

Yes, it is s bit messy offcourse.

[levis123]

Yes, it is s bit messy offcourse.

Ok I guess I can monitor the reaction with TLC, although I don't see how this will change what I get in the end.

[rolnor]

If the reaction is fast I agree. Its a bit special running reaction with sulphuric acid as solvent. Is it possible you collect the wrong product, did you get a good amount?