Re-investigation of the binary system Phenanthrene/Anthracene

Chemical purification of Phenanthrene can be achieved by conventional laboratory techniques, such as preparative HPLC. However, this process presents several drawbacks: i) tendency of adding solvent impurities to the targeted compound; ii) limitations in the separation, especially with other fused ring compounds such as Anthracene, Fluorene, etc. By contrast, the zone melting technique [1] has shown very interesting results in the ultra-purification of several inorganic solids (such as silicon, obtained with 99.999 % of purity) [2], while it is currently not widely used for organic compounds. This process, based on the segregation of impurities by phase separation, involves heterogeneous equilibria and requires a precise description of phase diagrams between the molecule to purify and its impurities. Zone melting experiments were conducted on Phenanthrene [3, 4] in order to remove its four main impurities: Dibenzothiophene, Carbazole, Fluorene and Anthracene. However, the binary phase diagrams between Phenanthrene and these compounds (described in the literature) were not well and/or fully described, leading us to a systematic re-investigation of these systems. The current study deals with the re-investigation of the Phenanthrene/Anthracene binary system, which was described in 1957 [5] as fully miscible in the liquid and in the solid state. One can note that this diagram was constructed without structural characterization of phases.