mackolol - 2-5-2020 at 13:47
Hi, I'm gaining interest in Palladium on carbon, It's not very expensive although it lasts "forever" and ommits the need to use expensive compounds
such as borohydrides or aluminumhydrides, or toxic such as mercury salts.
And my question is how is it really in usage, is it easy to recover from post syntheses mixtures and how big usually the loss may be.
Is it really efficient and is it comfortable in use?
What are reductions which Pd/C runs most effective?
[Edited on 2-5-2020 by mackolol]
AvBaeyer - 2-5-2020 at 19:01
Palladium on carbon is a very versatile catalyst if you understand how to use it and have the proper equipment. Many reductions can be carried out at
atmospheric pressure using the "balloon technique" as long as good mixing can be ensured. Obviously, more difficult hydrogenations require suitable
pressure equipment and a means to ensure good mixing such as a shaker. In all cases access to a mild vacuum (to remove air from the reduction
apparatus) and a pure hydrogen supply are essential. Sometimes you can use transfer hydrogenations and related types of reactions which do not
require a hydrogen source.
Fire is a constant potential hazard with Pd-C (and hydrogen) especially with volatile solvents such as methanol. There are particular ways that
catalyst, solvent and reactant are mixed prior to starting the reduction.
Work up of most reductions begins by evacuation the reduction apparatus and refilling with nitrogen. The reaction is the filtered under an inert
atmosphere through an inert support such as diatomaceous earth filter aid. Filtration through regular filter paper is completely inefficient and often
results in fire as the paper and catalyst dry out. If the paper method is used, the paper and catalyst are usually doused with water and then put into
a fire safe storage container.
Rarely can the used catalyst be recovered for further use. The "spent" catalyst and whatever it is attached to are generally sent back to the
manufacturer for recycling if you are a high volume user. For occasional use the spent catalyst is sent for incineration. It is not practical to spend
time and effort for any type of actual recovery and activation for reuse.
If you are really interested in learning about hydrogenation in general, I suggest you try to find the quite comprehensive book:
Paul N. Rylander, "Hydrogenation Methods," Academic Press, 1985.
Hope this helps.
AvB
mackolol - 3-5-2020 at 02:34
Okay, so it is not as practical as I have thought. If it would be for single use and had to be in all circumstances under inert or hydrogen atmosphere
it's either impractical and non economical for me. I would rather buy some hydrides which, to be honest are cheaper and more certain as well as safe
as for single use.
But why does it burn with everything when it has access to oxygen? Is it common for palladium?
Johnny Windchimes - 10-5-2020 at 11:00
Tom at Tom's Lab on Youtube has a decent video on it and it's prep. I've done it his way, it indeed works.
https://www.youtube.com/channel/UCnyhcAKKjIlydJzMfCe8DTw
S.C. Wack - 10-5-2020 at 12:50
Obviously one could buy both hydride and Pd and use the hydride to make the catalyst.
If one wanted to know about catalysts, perhaps they should read a Vogel or go to orgsyn and search there, even back to 1946? The literature doesn't
always agree with responses solicited from the internet.
They last neither forever nor once, unless they've been poisoned. It's easy to recover either way.
draculic acid69 - 10-5-2020 at 22:54
I never got the point of using hydrides to make other hydrides or add hydrogen into other catalysts. Its like going in circles to me