Purification of Phenanthrene

The likely contaminants of Phenanthrene (CAS NO. 85-01- include, anthracene, carbazole, fluorene and other polycyclic hydrocarbons. Purified by distn from sodium, boiling with maleic anhydride in xylene, crystn from acetic acid, sublimation and zone melting. Has also been recrystd repeatedly from EtOH, benzene or pet ether (b 60-70 °C), with subsequent drying under vacuum over P2O5 in an Abderhalden pistol. Feldman, Pantages and Orchin separated from most of the anthracene impurity by refluxing phenanthrene (671g) with maleic anhydride (194g) in xylene (1.25L) under nitrogen for 22h, then filtered. The filtrate was extracted with aqueous 10% NaOH, the organic phase was separated, and the solvent was evaporated. The residue, after stirring for 2h with 7g of sodium, was vacuum distd, then recrystd twice from 30% benzene in EtOH, then dissolved in hot glacial acetic acid (2.2mL/g), slowly adding an aqueous soln of CrO3 (60g in 72mL H2O added to 2.2L of acetic acid), followed by slow addition of conc H2SO4 (30mL). The mixture was refluxed for 15min, diluted with an equal volume of water and cooled. The ppte was filtered off, washed with water, dried and distd, then recrystd twice from EtOH. Further purification is possible by chromatography from CHCl3 soln on activated alumina, with benzene as eluent, and by zone refining.