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Theoretical and experimental investigation of the formation of E- and Z-Aldimines from the reaction of methylamine with acetaldehyde

Journal of the Brazilian Chemical Society, ISSN: 1678-4790, Vol: 10, Issue: 5, Page: 381-388
1999
  • 8
    Citations
  • 10,481
    Usage
  • 10
    Captures
  • 0
    Mentions
  • 0
    Social Media
Metric Options:   Counts1 Year3 Year

Metrics Details

  • Citations
    8
    • Citation Indexes
      8
      • CrossRef
        8
  • Usage
    10,481
  • Captures
    10

Article Description

The reaction of methylamine with acetaldehyde in pentane at 230 K leads to formation of both E- and Z- aldimines, the Z-isomer being the main product and generated upon kinetic control. The E- form is more stable than the Z- form by 3.3 kcal/mol (deltaG*). Ab initio calculations have indicated that a tetrahedral zwitterion intermediate is not formed, and the bimolecular process, forming the aminoalcohol intermediate, occurs through a four center transition state, with concerted formation of C-N bond and proton transfer. However, the predicted deltaG*¹ is very high, indicating that the true mechanism for this step is not bimolecular. A catalyzed pathway must be actuating. The following step, unimolecular elimination of water, also presents a very high activation free energy. Similarly, a catalyzed mechanism is needed. The isomerization from the Z- form to the E- form through inversion of the nitrogen atom has a predicted deltaG*¹ of 27.0 kcal/mol at 298.15 K, resulting in a lifetime of four months for the Z-isomer.

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