Solubility of p-t-butylcalixarenes in supercritical carbon dioxide: a comparison of static and dynamic measurement techniques

The solubilities of p-t-butylcalix[n]arenes (n=4,6,8) and calix[4]arene have been measured in supercritical carbon dioxide. Solubility measurements were conducted in a high pressure cell with in situ spectrophotometric detection. Measurements were taken over the ranges of 10 to 20 MPa and 40 to 60°C. The p-t-butylcalix[4]arene showed solubility approximately 10 fold higher than both p-t-butylcalix[6]arene and p-t-butylcalix[8]arene with a maximum measured solubility over the studied pressure and temperature ranges of 1.84×10−5 mol/l. A comparison of these results with measurements made with a commercially available analytical SFE unit for p-t-butylcalix[4]arene showed less than 10% deviation between the two sets of data over a common range of conditions. The SFE unit allows measurements to be made over significantly wider ranges of pressure and temperature than are currently available using the solubility cell.