QUANTITATIVE EQUILIBRIUM-CONSTANTS BETWEEN CO2 AND LEWIS-BASES FROM FTIR SPECTROSCOPY

Equilibrium constants measured from the nu(2) bending mode of CO2 by F TIR spectroscopy are reported for the electron donor-acceptor interact ions of CO2 with three Lewis bases: triethylamine(TEA), pyridine (PYR) , and tributyl phosphate (TBP). The average K-c values are 0.046 (CO2- TEA), 0.133 (CO2-PYR), and 1.29 (CO2-TBP) L/mol at 25 degrees C in the solvent pentane. For the CO2-TBP system, the average enthalpy of asso ciation, Delta H degrees, is -4.7 kcal/mol. Ab initio calculations ind icate that steric repulsion of the ethyl groups in TEA cause the bindi ng energy of the CO2-TEA complex to be weaker than that of the CO2-PYR complex by 1.34 kcal/mol, a trend that is in agreement with our spect roscopic data. The lattice fluid hydrogen bonding model was used in co njunction with the spectroscopically determined K-c values to predict bubble points for the CO2-TEA and CO2-TBP systems and CO2 sorption in a hypothetical polymer. These calculations indicate that these relativ ely weak specific interactions have a measurable effect on phase behav ior and can influence sorption of CO2 in polymers.