FireLion3
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How does Pd/C catalytic hydrogenations work?
I haven't been able to find much information about this online. Information that I have found is limited to saying that Pd/C reacts with h2 and then
reduces and hydrogenates organic compounds.
That is incredibly vague. Is there an actual mechanism at work here? How is h2 reacting with palladium and how does that react with an organic
compound to reduce it?
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alexleyenda
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If I remember my ochem class H2 dissociates into single hydrogen atoms that attach themselves on the surface of Pd or Ni or Pt. The carbon is only
there to make Pd less reactive. Once the hydrogen atoms are single on the surface of Pd, they can easily attack double bonded carbons fro example.
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chemaddict
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i would of thought the carbon was there because it has the ability to hold much more hydrogen on the surface then any metal would on its own.
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FireLion3
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Pd is put on carbon to maximize the surface area and increase the reaction, to my knowledge.
What I am not understanding quitely entirely is where are the electrons coming from that are reducing the organic compound?
Does the h2 rapidly react with Pd without much effort, and then the this alone can reduce the organic compound? Is it this simple?
OrganicCompound + H2 --pd/c--> Reduced/Hydrogenated Compound?
Is this exothermic?
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leu
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Four pages from Negishi's Handbook of Organopalladium Chemistry for Organic Synthesis are attached  These pages were found online along with many others  The end results from the effort applied 
Attachment: Pd-C.pdf (340kB)
This file has been downloaded 481 times
Chemistry is our Covalent Bond
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alexleyenda
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Quote: Originally posted by FireLion3  | Pd is put on carbon to maximize the surface area and increase the reaction, to my knowledge.
What I am not understanding quitely entirely is where are the electrons coming from that are reducing the organic compound?
Does the h2 rapidly react with Pd without much effort, and then the this alone can reduce the organic compound? Is it this simple?
OrganicCompound + H2 --pd/c--> Reduced/Hydrogenated Compound?
Is this exothermic?
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I took a look in my ochem book, it says Carbon is there to stabilise Pd as it is very reactive and might catch fire. Anyways if it would increase the
surface, we would also use Ni/C or Pt /C but Ni and Pt are used alone for hydrogenations so it makes sense. And yeah Leu's link is clear and more
complete for the explanation of how it works .
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FireLion3
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Indeed thank you for the link, leu. That is probably far more than what I asked for, as I feel it explained it "too much", haha.
I'm going to attempt to simplify my understanding of that article, so somebody correct me if I'm wrong.
Palladium reduces the H2, splitting them, and they go on to reduce and hydrogenate the organic compound. Whatever is broken off of the organic
compound then reduces the Palladium, so that it can reduce more H2?
It says the Palladium reduces each H atom to a negative one charge, which, would make them hydride ions in a way? Hydride ions are of course capable
of reducing and hydrogenating organic compounds. This would also explain why Pd/C has known to be flamable. Normal palladium may not have that much
surface area, but Pd/C is made to maximize surface area and absorb 900x its volume in hydrogen.
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Metacelsus
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Palladium is a catalyst, not a reducing agent. The hydrogen is not reduced, just absorbed onto the Pd.
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FireLion3
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Exactly. Palladium temporarily dissolves/separates the H2 so that it can gain or lose its electrons much more easily.
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