[sliorbra]

Hello,

Right now i'm studying the addition of hydrogen reaction of alkynes.
I've read that the reaction can be stopped at the alkene stage using Lindlar catalyst, which is prepeared by precipitating palladium on calcium carbonate and treating it with lead(II) acetate and quinoline.

can someone explain exactly how does it works? I mean, what is the mechanism of the reaction when these reagents are being used?? (and why the reaction stops at the alkene stage).
I've searched the mechanism all over the internet, but have'nt found anything.

Can someone help me with it??

thanks,
Lior.

[Guitarmaniac86]

The catalyst is partially de-activated which favours the addition of hydrogen up to the alkene stage. That's all I know, sorry if that isn't much help

[nox]

All my book says is that quinoline "poisons" the palladium, which I take to mean it probably forms some sort of deactivated complex, and significantly reduces palladium's reactivity.