Sciencemadness Discussion Board

functional groups on a benzene ring

lybra0076 - 29-9-2010 at 11:06

I am trying to do a synthesis with starting with a benzene ring. I pretty much have it figured out. I am adding NO2 onto the ring because it directs ortho and para, then, because I want to add CHO in the orth position, I need to add something else that will add in the para position. The two questions that I have go together 1. what group 2. how do I disconnect it after its use.

long story short....

I am not really aware of any disconnections of a functional group from on a benzene ring.

bbartlog - 29-9-2010 at 13:18

Although I don't know much about organic synthesis, I don't believe that it is normally a practical approach to use a protecting group (which is more or less what you're trying to do) in order to protect the para position or any other unmodified place on the benzene ring, simply because selectively removing whatever it is will be too difficult. You either need a different approach or else just a good way to separate the ortho and para products.
Also, if you want advice it helps to give more information, like what it is you're trying to synthesize, rather than just some piecemeal clues.

Quote:

I am not really aware of any disconnections of a functional group from on a benzene ring.


Benzoic acid (well, benzoates) can be decarboxylated by heat, and toluene likewise can be stripped of the carbon and turned back into benzene. There are also other reactions that seem to strip a functional group but I think often the result is a coupling reaction (or just a mess) as for example in the deamination of aniline to produce diphenylamine.

entropy51 - 29-9-2010 at 14:32

I'm not certain what you're trying to do, but you mention a nitro group. Sometimes a nitro group can be removed from the ring by reduction to an amino group, followed by a diazotization and removal as nitrogen gas by treatment with something like copper powder.