[AdiDex]

I was studying Wacker oxidation. I tried to search literature online. I found this open access paper.
https://www.sciencedirect.com/science/article/pii/S1319610316301016
I couldn't understand this,

the inevitable contamination caused by copper ions during this process has been recognized as a considerable limitation.

Which kind of contamination is this? Which reactions can be promoted by this Cu²⁺ and Cu⁺ ? Why couldn't those contaminations be separated efficiently?

[chenbeier]

In this classical system, the key step, reoxidization Pd(0) to active Pd(II) species was realized using copper salts as the oxidant.

They need copper for oxidation. But to much copper disturb the reaction on the organic molecules.

[wildfyr]

What they are saying is that copper salts were used to promote Pd to Pd(II) during early versions of this reaction. However copper salts are extremely reactive themselves and depending on your substrate can cause a myriad of side reactions.

Its not a matter of separating out the contamination after the fact, because while Cu(I)Cl is the oxidant, Cu(II) is being produced during the reaction on purpose, and causing whatever havoc it feels like. Cu(I) itself is also a pretty reactive species.

Googling "Copper catalyzed reactions" should give a rich demonstration of all the things copper salts can do. Its probably the most powerful (cheap) transition metal catalyst out there. Its not something you want in there willy-nilly.