soma
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incomplete glyoxal amide reaction
Wondering what the reactions between glyoxal amides and LAH are and if you would end up with if the LAH is somewhat decomposed.
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soma
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REACTION OF LiAlH4 WITH AN AMIDE
Step 1:
The nucleophilic H from the hydride reagent adds to the electrophilic C in the polar carbonyl group of the ester. Electrons from the C=O move to the
electronegative O creating an intermediate metal alkoxide complex.
reduction of an amide using hydride
Step 2:
The tetrahedral intermediate collapses and displaces the O as part of a metal alkoxide leaving group, this produces a highly reactive iminium ion an
intermediate.
Step 3:
Rapid reduction by the nucleophilic H from the hydride reagent as it adds to the electrophilic C in the iminium system. p electrons from the C=N move
to the cationic N neutralizing the charge creating the amine product.
http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch20...
[Edited on 17-8-2013 by soma]
[Edited on 17-8-2013 by soma]
[Edited on 17-8-2013 by soma]
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kristofvagyok
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If the LAH is decomposed we usually use excess of it. How much? Calculate it.
It could be easily titrated. Just add some precisely measured amount (e.g.: 0.1g) to methanol or ethanol and see how many hydrogen evolves (LiAlH4 +
3CH3OH => LiOMe + Al(OMe)3 + 4H2). For measuring the evolving gas, a gas burette should be used.
Another good idea is to use absolutized solvents for the reaction, because even traces of water could ruin the whole thing.
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bfesser
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Thread Moved
17-8-2013 at 15:20 |
chemrox
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Uhhh .. what is "absolutized?"
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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bfesser
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I gather, from the context, that he means it in the way of 'absolute' ethanol being anhydrous; "absolutized" being thoroughly dried.
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