An Extensible Framework for Capturing Solvent Effects in Computer Generated Kinetic Models

Detailed kinetic models provide useful
mechanistic insight into
a chemical system. Manual construction of such models is laborious
and error-prone, which has led to the development of automated methods
for exploring chemical pathways. These methods rely on fast, high-throughput
estimation of species thermochemistry and kinetic parameters. In this
paper, we present a methodology for extending automatic mechanism
generation to solution phase systems which requires estimation of
solvent effects on reaction rates and equilibria. The linear solvation
energy relationship (LSER) method of Abraham and co-workers is combined
with Mintz correlations to estimate ΔGsolv°(T) in over 30 solvents using solute descriptors estimated
from group additivity. Simple corrections are found to be adequate
for the treatment of radical sites, as suggested by comparison with
known experimental data. The performance of scaled particle theory
expressions for enthalpic–entropic decomposition of ΔGsolv°(T) is also presented along with the associated
computational issues. Similar high-throughput methods for solvent
effects on free-radical kinetics are only available for a handful
of reactions due to lack of reliable experimental data, and continuum
dielectric calculations offer an alternative method for their estimation.
For illustration, we model liquid phase oxidation of tetralin in different
solvents computing the solvent dependence for ROO• + ROO•
and ROO• + solvent reactions using polarizable continuum quantum
chemistry methods. The resulting kinetic models show an increase in
oxidation rate with solvent polarity, consistent with experiment.
Further work needed to make this approach more generally useful is
outlined.