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

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*<FONT FACE="Symbol">¹</FONT> 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*<FONT FACE="Symbol">¹</FONT> of 27.0 kcal/mol at 298.15 K, resulting in a lifetime of four months for the Z-isomer.

Bibliographic Details

Main Authors:	Pliego Jr.,Josefredo R., Alcântara,Antônio Flávio de C., Veloso,Dorila Piló, Almeida,Wagner B. de
Format:	Digital revista
Language:	English
Published:	Sociedade Brasileira de Química 1999
Online Access:	http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50531999000500008
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