Syncristallisation Organique avec Peritexie. Cas du Système Binaire Fluoro-2 Naphtalene - Naphtol-2

Abstract

The phase relations in the x 2-fluoronaphthalene-(1 - x) 2-naphthol system have been determined by X-ray diffraction, DTA and heating optical microscopy. Three stable solid phases occur: β which is a solid solution of 2-fluoronaphthalene in the low temperature form of 2-naphthol (OH_II), α which is a solid solution of 2-fluoronaphthalene in the high temperature form of 2-naphthol (OH_II) and α’ which is a solid solution of 2-naphthol in 2-fluoronaphthalene (F_I). The structure of the β phase is derived from the ordered structure OH_II (monoclinic, Ia, Z = 8) whereas the structure of the α and α’ phases are respectively derived from the disordered structures OH_I and F_I (monoclinic, P2₁/a, Z = 2). The main features of the phase diagram are a transition zone (II-I) for solid solutions rich in 2-naphthol, the limits of which at 293 K are x = 0.20 and x = 0.45 and a peritectic at T _p = 338 K with a miscibility gap from x = 0.60 to x = 0.87; the limits of demixion at 293 K are x = 0.53 and x = 0.95. This example points out that volume relationships are not decisive in organic solid-state solubilities. Le diagramme de phases du systeme x fluoro-2 naphthalene-(I - x) naphtol-2 a été déterminé par méthodes radiocristallographique, thermique et optique. Il est de type Roozeboom IV avec un péritectique situé à x = 0.87 et à T _p = 338 K. Il est caractérisé également par un phénomene de polymorphisme Il-I affectant des solutions solides riches en naphtol-2 (forme II: monoclinique, Ia, Z = 8 - forme I: monoclinique, P2₁/a, Z = 2, structure désordonnée). Cet exemple met en lumière l'insuffisance des seules considerations d'homéomorphisme moléculaire pour décrire les conditions de formation d'un cristal mixte organique.