Transferable force field for equilibrium and transport properties in linear and branched monofunctional and multifunctional amines. II. Secondary and tertiary amines

Following the same philosophy of our previous force field for primary amines (J. Phys. Chem. B2011, 115, 14617), we present an extension for secondary and tertiary amines using the anisotropic united atom (AUA4) approach. The force field is developed to predict the phase equilibrium and transport properties of secondary and tertiary amines. The transferability was studied for an important set of molecules including as secondary amines dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, and di-iso-butylamine. We have also tested diethylenetriamine, a multifunctional molecule which includes two primary and one secondary amino groups. For tertiary amines, we have included simulations for trimethylamine, triethylamine, tri-n-propylamine, and methyldiethylamine. Monte Carlo simulations in the Gibbs ensemble were carried out to study thermodynamic properties such as equilibrium densities, vaporization enthalpies, and vapor pressures. Critical coordinates (critical density and critical temperature) and normal boiling points were also calculated. The shear viscosity coefficients were studied for dimethyl, diethyl, di-n-propyl, trimethyl, triethyl, and tri-n-propylamine at different temperatures using molecular dynamics in the isothermal isobaric ensemble. Our results show a very good agreement with experimental values for all the studied molecules for both thermodynamic and transport properties, demonstrating the transferability of our force field.