1. Reductive amination is the go-to method for building an amine from a carbonyl.
Acetaldehyde plus methylamine gives N-methylethylamine.
2. The carbonyl and amine first condense to an imine, losing a molecule of water.
Condensation: aldehyde + amine → imine + H₂O.
3. A mild hydride then reduces the C=N in situ without touching the starting carbonyl.
NaBH3CN reduces the iminium selectively, so it works in one pot.
4. Choosing the nitrogen source sets whether you get a 1°, 2°, or 3° amine.
Acetone + ammonia → isopropylamine, a 1° amine.
5. Reductive amination cleanly avoids the over-alkylation that plagues direct alkyl-halide alkylation.
Acetone + methylamine → N-methylisopropylamine, a 2° amine.
Summary
Carbonyl + amine → imine (loses H₂O) · mild hydride (NaBH3CN or NaBH(OAc)3) reduces C=N in situ · one pot · NH₃→1°, 1° amine→2°, 2° amine→3° · beats over-alkylation.
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NaBH3CN is mild enough to reduce the protonated iminium but leaves the starting aldehyde or ketone untouched, so imine formation and reduction can happen together in one pot.
Water — the condensation to the imine (or iminium) releases one molecule of H₂O.
Isopropylamine, a primary (1°) amine, because ammonia contributes the nitrogen and the reduced C=N becomes a C–N bond.
Direct alkylation keeps reacting to give a messy mix of over-alkylated products, while reductive amination adds just one carbon group cleanly and stops there.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.