When the imine is stable enough, once it's formed, there's only little amounts of ketone/aldehyde around to get reduced. The NaBH4 isn't selective
enough to only reduce the carbonyl and displace the equilibrium, destroying the imine. It just reduces whats there in my experience. Removing water by
physical or chemical means ables the less stable imines to not reverse to the carbonyl and amine. Using cold, anhydrous conditions, MeOH or EtOH as
solvant with mol. seives or silica gel gives very satisfying results for different ketones (aromatic or aliphatic) with primary amines.
The so-called "wet" method only gave low yields, even when changing solvants, PTC or not, water/solvant ratio, amine/carbonyl ratios, etc.
Using dry, freebase amine, even if longer with gaseous amines, is the way to go. When correctly done, using a distilaltion setup with NaOH in
condenser and a addition funnel with conc. amine salt, solid NaOH in the still, and tubing attacjed to the vacuum inlet, you hardly get the smell if
you work cleanly. When using either MeOH or EtOH, it doesn't have to be very cold when gassing, 20°c is more than enough, all the gas is absorbed.
Or you can use triethylamine to base the amine salt insitu, though you have to fractionnate your freebases after workup to seperate the secondary
amine from the triethylamine.
Solo, have you tried the anhydrous way? You might be surprised. Although you working with what could be a delicate substarte.
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