Abstract
The separation of trace amounts of anthracene from phenanthrene is very difficult even with the zonerefining method. The authors have found that the addition of a small quantity of maleic anhydride to the original phenanthrene sample greatly enhances the efficiency of zone-refining.
Anthracene reacts with maleic anhydride in the melted zone of phenanthrene to form an addition compound whose segregation coefficient is much different from that of anthracene itself. Therefore, the efficiency of zone-refining is enhanced.
The determination of anthracene was made by measuring the absorbance at 376 nm in cyclohexane; the limit of detection by this method was 0.002%. A commercial sample of guaranteed-grade phenanthrene contained about 1.2% anthracene. After 30 passes of the sample through the heated zone in the presence of 2.8% maleic anhydride, no anthracene could be detected in the purified product.
The present technique of improving efficiency of the zone-refining method by adding a third substance which in the melted zone reacts with the impurity to form a compound of different segregation coefficient may be applied to various cases.
