Sciencemadness Discussion Board

How does Pd/C catalytic hydrogenations work?

FireLion3 - 11-1-2014 at 16:10

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?

alexleyenda - 11-1-2014 at 16:24

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.

chemaddict - 11-1-2014 at 16:37

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.

FireLion3 - 11-1-2014 at 16:42

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?

leu - 11-1-2014 at 17:42

Four pages from Negishi's Handbook of Organopalladium Chemistry for Organic Synthesis are attached :) These pages were found online along with many others :P The end results from the effort applied :cool:

Attachment: Pd-C.pdf (340kB)
This file has been downloaded 413 times

alexleyenda - 11-1-2014 at 18:49

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?



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 .

FireLion3 - 11-1-2014 at 19:41

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.

Metacelsus - 12-1-2014 at 06:56

Palladium is a catalyst, not a reducing agent. The hydrogen is not reduced, just absorbed onto the Pd.

FireLion3 - 12-1-2014 at 09:35

Exactly. Palladium temporarily dissolves/separates the H2 so that it can gain or lose its electrons much more easily.