Ochem Question

[Nat426]

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Problem SA-11 ACS study guide.

Same reaction DAT Destroyer Ochem (2010) #14

So both reactions add -NO2 to benzene (or start with it) i understand benzene is a meta director but it's also a deactivator. The next step in both reactions is a Friedel Crafts Alkylation... I understood that FC alkylations couldn't occur on a deactivated ring? I am also unsure what role the H2/Pt plays as it isn't catalytic hydrogenation. Can anyone shed some light on this? Thanks.

 

[Nat426]

So as i look at the questions, is the Br2/FeBr3 not considered a FC Alkylation... I guess not because no alkyl group is being added. But i'm still not sure the purpose of the H2/Pt that comes after. Does it just deactivate the acid catalyst so it wont continue to react?

 

[RCT PC CRN]

Follow the sequence below to get -NH2 and -X (Br, Cl) at meta position

HNO3,H2SO4 (-NO2 to Ring via Electronic Sub)
X2/FeX3 (Another Electronic Sub, since -NO2 is present, X will add to Meta)
H2, Pt (-NO2 to -NH2, reduction)

Additional note to the subject, you could further convert -NH2 to N2+ and then could do lot more reactions, change -N2+ to -OH, F, I, CN etc.

 

[Baylor2011]

Br_2/FeBr_3 is to add a halide to a benzene ring. Since you have a nitro group on the ring, it will add the meta position, and H_2/Pt is a reducing agent...change the nitro to an amine group.

Commenting on what RCT PC CRN said...to change NH_2 to N2 (triple bond) you use HONO (nitrous acid), I believe at 5 degrees celcius, or NaNO_2, HX. The following reactions are known as Sandmeyer reactions.

http://www.organic-chemistry.org/namedreactions/sandmeyer-reaction.shtm

 

[Nat426]

Thanks, i guess i was on track. I just never saw H2/Pt used as a reducing agent in anything other than catalytic hydrogenation. To reduce the -NO2 group i learned the use of activated metal with catalyst. i.e. Fe,Zn,Sn with Ni, Pt, Pd.

 

[Baylor2011]

Yes, other reducing agents are H_2/ Pt, Ni, or Pd/charcoal