Wondering what the reactions between glyoxal amides and LAH are and if you would end up with if the LAH is somewhat decomposed.soma - 17-8-2013 at 11:43
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.
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.chemrox - 24-2-2014 at 10:26
Uhhh .. what is "absolutized?"bfesser - 24-2-2014 at 10:36
I gather, from the context, that he means it in the way of 'absolute' ethanol being anhydrous; "absolutized" being thoroughly dried.
