The Hive > Serious Chemistry
CTH compilation, questions, future directions
Dope_Amine:
indole: Thanx for reminding me about that article. I need to sit down and read that. Funny that it came out so long ago.
Results: %60 :(
BUT, I've come to realize that she was recovering only about 50% of her Pd/C back and that means she was only using 5 (from previous rxn) grams this last time. Also, when she went to do the work-up, she came inside from a cold night with cold hands and felt the flask which she had moved a bit farther away from that refluxing flask and it was definitely warm :( :( . Again, the oil was a maroon color.
Next time it will bee done as said in my post above, with an ice bath, fresh Pd/C, alcoholic methylamine- not cuz she's worried abot water but just cuz, 'tone stirred for an hour, then Pd/C, and then let ice bath slowly warm to r.t......
Barium:
a) potassium or chlorine ions *could* affect the catalyst reactivity in some way.. (poisoning or maybe even positive effects?)
Which means that you are guessing.
b) if the acid is added to the ketone/imine/amine, "pockets" of acid could form due to insufficient mixing or too fast addition rate, resulting in temporary local overacidification. Not favorable. Surely nothing to bother with, but can be easily avoided by premixing amine and acid, mixing well (as Dope_amine said, one hour for paranoid bees ) and then adding the ketone, followed by the catalyst.
And then you miss the point of having about 1 eq free methylamine present to supress any side reactions. The reducing agent could be added at about the same rate as it is comsumed. The local over acidification would not likely be any problem with that much methylamine present.
About the IPA: Have you any personal experience of IPA as hydrogen donor with Pd/C? I have, and I can tell you it is a bitch to use as a hydrogen donor. With homogenous catalysts or nickel it is another story.
indole_amine:
And then you miss the point of having about 1 eq free methylamine present to supress any side reactions.
I surely don't miss any point here; I clearly stated that this order of reactands is not necessary in my opinion. Still overacidification *CAN* happen if the ketone is added before the acid. And this can be avoided. Although I don't consider it being important.
Is there any advantage of adding only small amounts of HCOOH while it is consumed? Do you have any experience with it? Are you just guessing?
Further I never said that IPA would be a suitable hydrogen donor in this case; I just said that due to its lack of inertness, it is not the solvent of choice here. As you said, it is a bad hydrogen donor - but it is one! And it is NOT favourable to conduct this reaction with a proportionally increasing amount of water - believe me or not. I don't even know exactly what happens to the IPA (acetone? Propane?) as I never wanted to know - because I already know that it is both a poor hydrogen donor and a poor solvent in this case.
indole_amine
indole_amine:
Stoichiometric, Catalytic, and Enantioface-Selective Hydrogenation of C=N Bonds by an Ionic Mechanism
(Magee, M. P.; Norton, J. R.)
J. Am. Chem. Soc., 2001; 123(8); 1778-1779
DOI:10.1021/ja003630+
"The hydrogenation of carbon-carbon double bonds is a classic application of homogeneous catalysis, and numerous complexes are known to catalyze it. Furthermore, the use of chiral ligands to produce enantioface selectivity in such catalytic hydrogenations is now well developed.1 The catalytic cycle for such reactions involves an olefin dihydride complex (with the addition of H2, step A, and the coordination of the olefin, step B, occurring in either order), giving the hydrogenated product by insertion and reductive elimination..."
:)
indole_amine
indole_amine:
Well, that's a pretty wierd one - the title seemed very fascinating to me... :)
(translated to "hive-conform" syntax, it would be an imine formation with subsequent rhodium-catalyzed borohydride reduction i guess.. ;) )
Ambient Temperature, Tandem Catalytic Dehydrocoupling-Hydrogenation Reactions Using Rh Colloids and Me2NH·BH3 as a Stoichiometric H2 Source
(Jaska, C. A.; Manners, I.)
J. Am. Chem. Soc. 2004; 126(9); 2698-2699
DOI:10.1021/ja039696x
Abstract
Highly active Rh colloids, generated in situ during the catalytic dehydrocoupling of Me2NH·BH3 using [{Rh(cod)(-Cl)}2] as a precatalyst, are capable of efficiently hydrogenating alkenes at 25 C in a one-pot procedure using only the evolved H2 from the initial dehydrocoupling reaction.
Now what about using RuCl2/methylammonium borohydride for a CTH reductive amination like described above? (just an idea)
indole_amine
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