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
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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.
Bibliographic Details
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50531999000500008&lng=en&nrm=iso&tlng=en; http://www.scielo.br/pdf/jbchs/v10n5/a08v10n5.pdf; http://dx.doi.org/10.1590/s0103-50531999000500008; http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50531999000500008&lng=en&tlng=en; http://www.scielo.br/scielo.php?script=sci_abstract&pid=S0103-50531999000500008&lng=en&tlng=en; http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50531999000500008; http://www.scielo.br/scielo.php?script=sci_abstract&pid=S0103-50531999000500008; https://dx.doi.org/10.1590/s0103-50531999000500008; https://www.scielo.br/j/jbchs/a/txz5KQKYzdwCM8VJzVvB96k/?lang=en
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