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Nitrobenzene reduction with (tin) Sn catalyst: Why is C-H bond cleavage preferred over O-H bond cleavage?
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Lillian Hafner
Nitrobenzene reduction with (tin) Sn catalyst: Why is C-H bond cleavage preferred over O-H bond cleavage?
I don't buy that mechanism. Like you noted, breaking a C-H bond in methanol seems unlikely, especially since the reaction is run in the presence of acid, so a ready source of protons is available.
Most of these reactions that involve a metal surface proceed through what is known as a single electron transfer (SET) mechanism. Reductions of nitro compounds, be they catalytic hydrogenations or metal surface - acid catalyzed reductions, usually proceed through nitroso and hydroxylamine intermediates. This link provides some discussion of the reaction and presents the following (more reasonable) mechanism where electrons are transferred from the metal surface to the various intermediates and the acid provides a ready source of protons. These reactions are usually run in an organic solvent in order to bring the organic nitro compound into solution.
I don't buy that mechanism. Like you noted, breaking a C-H bond in methanol seems unlikely, especially since the reaction is run in the presence of acid, so a ready source of protons is available.
Most of these reactions that involve a metal surface proceed through what is known as a single electron transfer (SET) mechanism. Reductions of nitro compounds, be they catalytic hydrogenations or metal surface - acid catalyzed reductions, usually proceed through nitroso and hydroxylamine intermediates. This link provides some discussion of the reaction and presents the following (more reasonable) mechanism where electrons are transferred from the metal surface to the various intermediates and the acid provides a ready source of protons. These reactions are usually run in an organic solvent in order to bring the organic nitro compound into solution.
No problem, though I have to say, I really dislike SET mechanisms. There is too much unknown about them, they seem to involve some kind of magic... (And I also would suggest, that the nitroso intermediate will be skipped in this.)More
I would expect the oxygen to be protonated all the way, at least to the major extent. In your scheme you go from $$\ce{R-N(OH)(OH2)+ ->[-\ce{H2O;\ - H+}] R-N=O ->[+\ce{H+}] R-N=OH+ },$$ but I would assume that it proceeds like this: $$\ce{R-N(OH)(OH2)+ ->[-\ce{H2O}] R-N=OH+ <=>[\pm\ce{H+}] R-N=O}$$ So you can trap the nitroso compound, but it is not actually part of the mechanism.More
@Martin No particular reason, it was an available drawing of the mechanism and zinc, tin , mercury amalgam, etc. should all proceed by the same mechanism.More
I don't buy that mechanism. Like you noted, breaking a C-H bond in methanol seems unlikely, especially since the reaction is run in the presence of acid, so a ready source of protons is available.
Most of these reactions that involve a metal surface proceed through what is known as a single electron transfer (SET) mechanism. Reductions of nitro compounds, be they catalytic hydrogenations or metal surface - acid catalyzed reductions, usually proceed through nitroso and hydroxylamine intermediates. This link provides some discussion of the reaction and presents the following (more reasonable) mechanism where electrons are transferred from the metal surface to the various intermediates and the acid provides a ready source of protons. These reactions are usually run in an organic solvent in order to bring the organic nitro compound into solution.
I don't buy that mechanism. Like you noted, breaking a C-H bond in methanol seems unlikely, especially since the reaction is run in the presence of acid, so a ready source of protons is available.
Most of these reactions that involve a metal surface proceed through what is known as a single electron transfer (SET) mechanism. Reductions of nitro compounds, be they catalytic hydrogenations or metal surface - acid catalyzed reductions, usually proceed through nitroso and hydroxylamine intermediates. This link provides some discussion of the reaction and presents the following (more reasonable) mechanism where electrons are transferred from the metal surface to the various intermediates and the acid provides a ready source of protons. These reactions are usually run in an organic solvent in order to bring the organic nitro compound into solution.
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