Reductive aminations proceed often in acidic media, or sometimes even in neat organic acid such as AcOH. Since reductive amination includes a
nucleophilic addition of the amine to the carbonyl carbon to form the hemiaminal, wouldnt the acidic environment of the reaction prevent this from
occuring due to protonation of the amine? I know acidic catalyzes the reduction of the schiff base, but Im just confused how the aminal forms when
most of the amines in solution are likely protonated.
Since reductive amination includes a nucleophilic addition of the amine to the carbonyl carbon to form the hemiaminal, wouldnt the acidic environment
of the reaction prevent this from occuring due to protonation of the amine?
Your question is not specific enough for an exact answer, because "reductive amination" is a name for all reductive transformations of ketone or
aldehyde functional groups to amino groups. There are numerous reagents, methods and conditions to do this and not all involve acidic media. However,
from your post I can see that you think that amines get protonated quantitatively with weak acids such as the acetic acid or at pH from 3 to 5 (as
required for the reduction with NaCNBH3). This is not the case. Protonation is an equilibrium reaction of which the equilibrium is
described by pKa values. Even in acetic acid as the solvent, amines are not quantitatively protonated. They are probably even less protonated as they
would be with an equivalent of acetic acid in water as solvent (the acetate is a stronger base in acetic acid than it is in water).
