title: Quantitative First-Principles Kinetic Modeling of the Aza-Michael Addition to Acrylates in Polar Aprotic Solvents.
abstract: This work presents a detailed computational study and kinetic analysis of the aza-Michael addition of primary and secondary amines to acrylates in an aprotic solvent. Accurate rate coefficients for all elementary steps in the various competing mechanisms are calculated using an ONIOM-based approach in which the full system is calculated with M06-2X/6-311+G(d,p) and the core system with CBS-QB3 corrected for solvation using COSMO-RS. Diffusional contributions are taken into account using the coupled encounter pair model with diffusion coefficients calculated based on molecular dynamics simulations. The calculated thermodynamic and kinetic parameters for all forward and reverse elementary reactions are fed to a microkinetic model giving excellent agreement with experimental data obtained using GC analysis. Rate analysis reveals that for primary and secondary amines, the aza-Michael addition to ethyl acrylate occurs preferentially according to a 1,2-addition mechanism, consisting of the pseudoequilibrated formation of a zwitterion followed by a rate controlling amine assisted proton transfer toward the singly substituted product. The alternative 1,4-addition becomes competitive if substituents are present on the amine or double bond of the acrylate. Primary amines react faster than secondary amines due to increased solvation of the zwitterionic intermediate and less sterically hindered proton transfer.
authors.affiliation: Laboratory for Chemical Technology, Ghent University , Technologiepark 914, B-9052 Gent, Belgium.
authors.forename: Gilles B
authors.identifier: 0000-0001-8946-1679
authors.initials: GB
authors.lastname: Desmet
authors.affiliation: Laboratory for Chemical Technology, Ghent University , Technologiepark 914, B-9052 Gent, Belgium.|Department of Textiles, Ghent University , Technologiepark 907, B-9052 Gent, Belgium.
authors.forename: Dagmar R
authors.initials: DR
authors.lastname: D'hooge
authors.affiliation: Polymer Chemistry Research Group, Ghent University , Krijgslaan 281 S4-bis, B-9000 Gent, Belgium.
authors.forename: Pinar Sinem
authors.initials: PS
authors.lastname: Omurtag
authors.affiliation: Polymer Chemistry Research Group, Ghent University , Krijgslaan 281 S4-bis, B-9000 Gent, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Espeel
authors.affiliation: Laboratory for Chemical Technology, Ghent University , Technologiepark 914, B-9052 Gent, Belgium.
authors.forename: Guy B
authors.identifier: 0000-0002-6733-1213
authors.initials: GB
authors.lastname: Marin
authors.affiliation: Polymer Chemistry Research Group, Ghent University , Krijgslaan 281 S4-bis, B-9000 Gent, Belgium.
authors.forename: Filip E
authors.identifier: 0000-0003-4065-6373
authors.initials: FE
authors.lastname: Du Prez
authors.affiliation: Laboratory for Chemical Technology, Ghent University , Technologiepark 914, B-9052 Gent, Belgium.
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Reyniers