Use of Sodium to Remove Anthracene and Other Impurities from Phenanthrene SIR: As recovered from tar, phenanthrene contains anthracene, carbazole, fluorene, dibenzothiophene, their homologs, and other impurities. Even commercial purified samples contain varying amounts of these impurities. The usual purification procedure involves one step to remove anthracene (3, 10, f4), followed by fusion with sodium to remove fluorene (8) and sulfur-containing compounds (9, f I ) . Surprisingly, it has not been realized that sodium treatment also removes anthracene. Ultraviolet spectral analysis of phenanthrene purified with sodium revealed that the anthracene content had been markedly lowered. Because we could find no mention of this in the literature, we studied this simple and efficient purification procedure in some detail. Samples of phenanthrene purified in this way should prove of value for various physicochemical, particularly spectral ( 2 , 4, f 3) , measurements. EXPERIMENTAL
Treatment of Impure Phenanthrene with Molten Sodium. T h e phenanthrene samples used were from Rutgerswerke, A . G., West Germany. For some runs, a simulated crude phenanthrene (containing anthracene, 8.3; carbazole, 1.0; fluorene, 1.2; and dibenzothiophene, 1.0%) was made by melting a n d stirring together known amounts of these compounds with as-received phenanthrene; the mixture was then allowed to solidify. For a typical purification, a 500-ml., 3-necked, round-bottom flask was fitted with a Tru-bore stirrer and a n air condenser topped by a mercury bubbler. Prepurified N2 (50.1% 0 2 ) mas used to flush the apparatus, N a was added, and the third neck of the flask was fitted with a thermometer. For the remainder of the reaction, the apparatus was kept under a slight pressure of Nz. As the mixture was being stirred and maintained at about 200" C., the color of the molten mass darkened until it was quite black. At the end of the reaction, the mixture was cooled under Nz. A Claisen head with a 12-inch Vigreux column (wrapped with heating tape) was fitted into the flask. A receiver with a wide-mouth sidearm was attached to the distillation column. At a pressure near 1 mm. Hg, phenanthrene distilled over a t about 115' C. The distillation was stopped when the vapors rising up the column assumed a purplish tinge. A Bunsen burner was used where necessary to heat the flask and column sidearm to melt any condensed phenanthrene. Recoveries ranged from 67 to 8470.
Spectrometric Analyses of Purified Phenanthrene. For t h e low concentrations of anthracene, UV spectral analyses on a Cary Model 11 were made using concentrated solutions of phenanthrene in a 10-cm. pathlength cell. A t 70 grams of phenanthrene per liter, t h e usual concentration analyzed, a n anthracene content of O . O O O l ~ G gives a peak height a t 373 mp of two divisions above the base line. One sample, whose spectrum was measured on a solution containing 200 grams of phenanthrene per liter of benzene, had
