ORGO question

[ems5184]

Advertisement - Members don't see this ad

Okay so I was practicing the organic chem section and came across this question. This molecule (a benzene ring with two nitro groups that are meta to each other) is treated with (NH4)2S and the answer has the starting compound with one of the nitro groups reduced to an amino group.

1) I was wondering if both of these nitro groups could be reduced if an excess amount of NH42S was present?

2) Also, on the DAT, is it assumed to be one equivalent of a reactant unless otherwise specified?

3) Just for fun, if catalytic hydrogenation were used, (I know on a simple benzene ring it reduces all double bonds to yield a cyclohexane), but does anyone have any idea what it would do in this case?

 

[Sprgrover]

Yes, unless specified, assume one equivalent of (NH4)2S, which will give an amine. If excess is supplied, then the other nitro group should be reduced as well. In regards to catalytic hydrogenation there are two things to consider. If you were to toss in something like H2 and PdC (carbon on palladium or platinum as the catalyst) then the only things that will react are your nitro groups forming NH2. Benzene rings are HIGHLY stable. So stable and favored are such arrangenments that reactions whose transition states mimic aromatic compounds, i.e. Diels-Alder reactions, are very favorable. Thus, to go break such a stable form (thermodynamically unfavorable) one is going to have to beat the heck out of the compound: supply a lot of energy, at high pressures, give it a lot of time, and use a strong catalyst such as H2 and RhC (which would clearly reduce the functional groups first). Watch out, reducing a benzene ring is not that easy. I would say for purposes of the DAT, you will see a benzene ring's functional groups reduced but not the ring itself.

 

[sinned]

Sprgrover, when you just said "reducing" in your second to last sentence, what were you thinking? Reducing as in gain of electrons, loss of hydrogen, or loss of oxygen?

I haven't finished the second part of Orgo yet, taking summer school right now...so trying to learn every bit of it as possible...

Den

 

[DrTacoElf]

catalytic hydrogenation of benzene rings is not favorable (loss of aromaticity). As far as i know it only occurs with ruthenium or rhodium as a catalyst. Nitro groups will be reduced to amino groups.

Gaining of H = Reduction

 

[Sprgrover]

The nitro group is being reduced to an amine. Taco was right in his definition. A short cut to this problem (though this is not always the case) is to quickly look at the compound. We are knocking off those two oxygens, replacing them with two hyrdogens, and restoring the nitrogen's lone electron pair, which it loves 😍 . Thus, reduction. The vocabulary of organic chemistry can be tricky. Best of luck!

 

[sinned]

oh ok...I get it now...my definition was wrong 🙂