[diogotcarv]

Hello! I am facing troubles with the reduction of a o-nitrophenol to a o-aminophenolwhich has sensitive groups to catalytic hydrogenation. I succeded using stannous chloride (TLC) but the work upis really a mess. I poured the cooled reaction mixture in ice cold water and added sodium bicarbonate up to pH 7 (not to ionize phenol) but the stannous hydroxide precipitates and it is nor easily filtered. When I try to extract the mixture with ethyl acetate or  others, I get an emulsion hard to break down even with sat. NaCl. This is pushing down the reaction yields! I need *delete me*

[clarkstill]

SnCl2 workups are a real b***h. The best results I've had on scale have been by diluting into a large volume of EtOAc and then either (i) adding a huge volume of aq. NaHCO3, so much that the emulsion (which never dissolves) is well-enough dispersed for separation or (ii) adding the NaHCO3 dropwise and swirling - the insoluble SnClOH crashes out of solution with each drop - until the precipitate starts to combine with the water to make a sticky residue on the bottom of the conical flask. Then I decant the organic layer off the top and filter it over sand, and wash the sticky residue a few more times with EtOAc and filter over sand again. Finally I do a normal workup with NaHCO3 on the washings, and it normally comes out clean with no more precipitate problems. Don't add too much water in the dropwise addition, or else decanting the organic layer becomes tricky. I'd recommend method (ii) more highly.

Hope this helps!

[discodermolide]

It may be worthwhile trying other reduction systems see http://en.wikipedia.org/wiki/Reduction_of_nitro_compounds.

But it depends, of course, on the rest of your molecule.

[Dan]

I've worked with a couple of 2-nitroanilines before and they just wouldn't behave with the usual Fe, Zn, or H₂/Pd systems I would normally use.  The only thing that worked well was SnCl₂/HCl. It wouldn't surprise me if this was the OP's last resort as well...

(In my case, my molecule was not sensitive to base and I quenched with ice and then basified 10 M NaOH and extracted. I don't remember precipitates causing a real issue, but this was only ever on small scale (<1 g) so I can't really help.)

[pgk]

If you cannot avoid reduction with tin reagents, due to sensitive groups to catalytic hydrogenation: After the end of the reduction, you can add concentrated ammonia solution (phenols do not form ammonium salts) until alkaline to litmus (not pH = 7 that favors the formation of colloidal and pasty Zn(OH)2),  and filter under vacuum, with a Buchner. Supplementary addition of a solid diluent e.g. Celite, that helps the filtration, might be necessary.
PS:Nitro group reduction can also be effectuated in good yields, by metallic tin and concentrated HCl.