DETERMINATION OF HENRYS LAW CONSTANTS BY EQUILIBRIUM PARTITIONING IN A CLOSED-SYSTEM USING A NEW IN-SITU OPTICAL ABSORBENCY METHOD

A new method for measurement of thermodynamic Henry's law constants (H ) is reported. In this method, the optical absorbance of a dilute aque ous solution containing an organic compound is followed with time as t he compound partitions into the air above the solution in a sealed ves sel. The change in optical absorbance (i.e., change in concentration) and the vapor to liquid volume ratio of the vessel are then used to ca lculate the value for H. The concentration of the organic compound in the aqueous and vapor phases need not be known. This method allows the approach to equilibrium to be observed in real time so that attainmen t of equilibrium is readily apparent. This method works particularly w ell for water-soluble compounds having low vapor pressures. The applic ability of this method is limited to compounds that exhibit significan t optical absorbance in the ultraviolet and visible regions of the ele ctromagnetic spectrum. Values for H and their temperature dependencies measured using this new method are reported for methacrolein, methyl vinyl ketone, benzaldehyde, and acetophenone. Values for H are also re ported for benzene, toluene, and ethylbenzene at 298 K. All reported H data are compared with previously reported values.