Experimental determination of Henry's law constants of trifluoroacetic acid at 278–298 K

Equilibrium partial pressures of trifluoroacetic acid (PCF3C(O)OHPCF3C(O)OH) over aqueous trifluoroacetic acid test solutions were determined at 278.15, 288.15, and 298.15 K. The concentration of undissociated trifluoroacetic acid (CCF3C(O)OHCCF3C(O)OH) in each test solution was determined by means of attenuated total reflection IR spectroscopy and window factor analysis. From the linear relationship between PCF3C(O)OHPCF3C(O)OH and CCF3C(O)OHCCF3C(O)OH, the Henry's law constant of trifluoroacetic acid (KH) at 298.15 K was determined to be 5800±700 mol dm−3 atm−1 and KH at temperature T in K was determined to be KH=5780 exp[−4120×(1/298.15−1/T)] in mol dm−3 atm−1. The KH value at 298.15 K was 0.65 times the reported value [Bowden, D.J., Clegg, S.L., Brimblecombe, P., 1996. The Henry's law constant of trifluoroacetic acid and its partitioning into liquid water in the atmosphere. Chemosphere 32, 405–420] for pKa=0.47 and it was equal to that for pKa=0.2.