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Author: Subject: useing a bubbler?
beastmaster
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[*] posted on 11-7-2008 at 22:53
useing a bubbler?


Im going to do a catalysts h2 transfer reaction, I have a bubbler to monitor the gas rate. My question is, do I use water, or something else in my bubbler? I can't find any info on this subject. I have been getting a little more advance with each experiment, but I am still learning(and having fun.) I am getting ready to make the ammonium formate. I'm doing all my reactions on the micro level. thank you for any help

[Edited on 11-7-2008 by beastmaster]
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kclo4
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[*] posted on 12-7-2008 at 01:53


what is a hydrogen transfer reaction?
I searched, but nothing came up that seemed to describe what you seem to be doing, or what would be with in reach.
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Klute
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[*] posted on 12-7-2008 at 05:42


He is refering to a CTH (Catalyzed Transfert Hydrogenation) I suppose, where gaseous H2 is replaced by a hydrogen donor (formates, IPA, alkenes, etc).

I usuallu use dH2O in the bubblers with such reaction (CTH with formates), but you could just aswell sue mineral oil, as the water dissolves quite some CO2 (amm formates) and H2. If you want a precise monitering of the gas evolution, better use mineral oil.

Actually, any liquid that isn't too volatil or viscous is good. If you are going to use amm. formate, beware that the gas evolved will be a mixture of CO2 and H2. You could measure the amount of CO2 evolved by bubbling it through an exces of KOH solution, then neutralizing the solution and collecting the CO2 evolved in a inverted cylinder.
Or maybe collect all the gas under an inverted cylinder, note the volume, and add exces conc. KOH to the water, letting time for all the CO21 to be absorbed, and noting the volume of H2 left. But that would be some hassle, just use TLC to moniter the reaction.

I have found that 10:2:1 DCM:AcOEt:MeOH to be a very effective eluant for amines produced by CTH reduction of aliphatic nitroalkanes.

I would suggest to not heat the reaction with amm. formate to avoid deposition of amm. carbonate, bbut let it run at RT for 12-24H. I have done this following Stoechiometric_Steve's advice, and it worked very well, the workup was a charm.




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