UV/Vis spectra and solubility of some naphthoquinones, and the extraction behavior of plumbagin from Plumbago scandens roots in supercritical CO2.

The solubility of 1,4-naphthoquinone, plumbagin, lawsone, and juglone in supercritical carbon dioxide was determined spectroscopically at 40 degrees C, and in the pressure range 8-18 MPa. Their solubilities at 12 MPa were between 0.3 and 10 g L(-1). Plumbagin from Plumbago scandens L. roots was extracted at 40 degrees C and 20 MPa. The extracted plumbagin mass fraction was up to 0.2% in fresh roots but down to about 0.006% in aged roots. n-Hexane and chloroform extraction of such aged roots indicates that the older and dryer the roots are, the stronger they bind plumbagin. Reversed-phase HPLC indicated a relatively pure plumbagin extract with supercritical carbon dioxide.