Química Orgânica 2 · Síntese e transformação de aminas
Reductive amination — acetone and methylamine
Condições: Acetone and methylamine condense with a water-mediated proton relay, then hydronium is added. A separate formal reduction of the isolated iminium ion follows. Only one B–H transfer from BH₄⁻ is shown, not a proposed one-pot reaction: ordinary borohydride is not generally stable or iminium-selective in strongly acidic solution. The waters show where the oxygen and hydrogen atoms end up, not a complete reduction medium. Stop before borane association or quench; counterions are omitted spectators. No asymmetric induction is assumed.
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Carbonyl and nitrogen encounter
The amine lone pair supplies the new C–N bond. The carbonyl pair moves to oxygen.
As setas curvas
- The amine lone pair supplies the new C–N bond.
- The carbonyl pair moves to oxygen.
Solvent-mediated proton exchange
Water accepts an N-bound proton as part of the coupled relay. The N–H pair restores the nitrogen lone pair. Alkoxide accepts a water proton in the same relay. The departing O–H pair replenishes the solvent oxygen lone pair. Water mediates a coupled relay. No isolated hydronium/alkoxide pair or direct unassisted N-to-O proton transfer is implied.
Nota: Water mediates a coupled relay. No isolated hydronium/alkoxide pair or direct unassisted N-to-O proton transfer is implied.
As setas curvas
- Water accepts an N-bound proton as part of the coupled relay.
- The N–H pair restores the nitrogen lone pair.
- Alkoxide accepts a water proton in the same relay.
- The departing O–H pair replenishes the solvent oxygen lone pair.
Acid stage
The hydroxy oxygen accepts a hydronium proton. Hydronium returns to neutral water. Hydronium is added here. Its spectator counteranion is omitted throughout.
Nota: Hydronium is added here. Its spectator counteranion is omitted throughout.
As setas curvas
- The hydroxy oxygen accepts a hydronium proton.
- Hydronium returns to neutral water.
Continue the condensation branch
Nitrogen donates its pair to form the C=N bond. The C–O pair departs onto the oxygen of neutral water.
As setas curvas
- Nitrogen donates its pair to form the C=N bond.
- The C–O pair departs onto the oxygen of neutral water.
Formal reduction of the isolated iminium ion
The B–H pair makes a carbon–hydrogen bond at electrophilic iminium carbon; no free hydride is released. The iminium pi pair returns to nitrogen as carbon gains hydrogen, preserving both octets and giving a neutral amine. Condensation has ended. BH₄⁻ is added only for this separate formal reduction of the isolated iminium ion. This does not imply BH₄⁻ stability or selective one-pot reduction in acid. Waters remain to show the fate of their atoms. Borane association and quench are not shown.
Nota: This is a separate formal reduction, not an acidic one-pot borohydride reaction. Waters remain to show the fate of their atoms; the drawing does not specify which borane species exist in solution.
As setas curvas
- The B–H pair makes a carbon–hydrogen bond at electrophilic iminium carbon; no free hydride is released.
- The iminium pi pair returns to nitrogen as carbon gains hydrogen, preserving both octets and giving a neutral amine.
Secondary amine at the transfer endpoint
The carbonyl carbon now bears nitrogen and the transferred hydride. The original oxygen remains in water with a solvent proton and the acid proton, while the solvent shuttle retains the original N proton. Nitrogen has three sigma bonds and a lone pair; BH₄⁻ becomes the formally neutral BH₃ fragment. Every atom from the added reagents is retained.
O que você vai praticar
Join carbinolamine formation and dehydration to a formal isolated-iminium hydride transfer, retaining carbonyl oxygen in water.
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