Modeling Temperature Dependency of Amine Basicity Using PCM and SM8T Implicit Solvation Models

PCM and SM8T continuum solvation models are used to study the temperature dependency of a set of amines in the temperature range 273-393 K using density functional theoretical calculations. Gaseous phase calculations are done using B3LYP and M06 functionals at the 6-311++G(d,p) basis set level. pK(a) values calculated computationally are compared with experimental values in the given temperature region using both continuum solvation models. The continuum solvation models predict the temperature trends of pKa compared to experimental trends very nicely. Accurate pK(a) values at 298 K are however required as input to the model. The absolute values of pK(a) values are not reproduced well by these continuum solvation models, and a correction term is therefore introduced. A set of 10 amines, which have potential for CO2 capture, and where also a large experimental data set of temperature dependent pK(a) values is available, were studied in this work. The temperature dependency of pK(a) values of amines provides a basis for selection for optimum solvents for postcombustion CO2 capture processes.