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Topic: Catalytic hydrogenation with trityl group  (Read 4595 times)

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Offline Aminooxy

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Catalytic hydrogenation with trityl group
« on: September 01, 2011, 01:55:51 PM »

Just wondering if anyone has more experience in this type of reaction than I do. Currently I'm trying to remove a benzyl carbamate (Cbz-) from a primary amine and a benzyl ester in the presence of a 2-chloro-trityl protected primary amine.

The issue is that I've performed the hydrogenation up to 8hrs. at room temperature and continually have some of the carbamate left. I've heard that the trityl protecting group can be removed under these conditions, but have yet to see it happen. Should I be concerned about letting the reaction stir longer (say, overnight) without losing the trityl protecting group?

Offline Dan

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Re: Catalytic hydrogenation with trityl group
« Reply #1 on: September 02, 2011, 03:27:38 AM »
I'd try the longer reaction on a small amount of material and see how it goes. I assume your catalyst is Pd/C? I think Tr will only cleave very slowly at rtp, even benzhydryl (diphenylmethyl) cleaves very slowly compared to benzyl. You will probably get away with it.

You may also want to try Rh/C as the catalyst. Apparently this should not cleave Tr, but I don't know if it will reduce the C-Cl bond as well - check before you try it.
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Offline fledarmus

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Re: Catalytic hydrogenation with trityl group
« Reply #2 on: September 02, 2011, 11:39:28 AM »
Different hydrogenation catalysts from different companies can have very different activities. Even if you're using, for example, 10% Palladium on Carbon, the activity of the catalyst can be different depending on the source and the type of charcoal that was used to prepare it, and whether it is a dry or wet catalyst.

I've found that the Degussa type catalysts (50% water) are actually better for most of my amine deprotections than dry catalysts. You're usually using so little catalyst that even at 50% water, it's a very tiny amount.

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