The phase-diagram of the benzidine-0~-naphthol system, determined by the thaw-melt method, shows the formation of a 1:1 addition compound surrounded by two eutectics. From the linear velocity of crystallization data on pure components, eutectics and the addition compound, determined by the capillary method at different undercoolings, it can be inferred that they obey the Hillig-Turnbull equation. The X-ray diffraction studies suggest that the eutectics are not simply mechanical mixtures of two components. Heats of fusion data on the pure components, eutectics and addition compound, determined by differential scanning calorimetry, show that there is an associative interaction between the two components forming the eutectic melt. While the microstructural studies reveal that the microstructures of eutectics and the addition compound differ widely from those of the parent components, the spectral investigations suggest intermolecular hydrogen bonding between the two components.

The phase diagrams of binary organic systems of benzidine with pyrogallol and p-nitrophenol give a double simple euteetic type phase diagram showing formation of a I: 1 molecular complex with congruent melting point and two eutectics. The growth data on the pure components, the euteetics and the molecular complexes, determined by measuring the rate of movement of growth front in a capillary, justify the square relationship between growth velocity and undereooling. While enthalpy of mixing values suggest intermoleeular hydrogen bonding, the excess thermodynamic functions reveal strong interactions among the components forming euteeties and addition compounds.

No abstract

U. S. RAI and SANTHI GEORGE. Can J. Chem. 70, 2869 (1992.The phase diagrams of the binary organic system of benzidine-pyrogallol was determined by the thaw-melt method. The solidification behaviour of the pure components, their eutectics, and the addition compound were studied by measuring the movement of growth front in a capillary. From the data on X-ray diffraction, thermal and microscopic investigations it can be inferred that the eutectics are not simple mechanical mixtures of the components involved. The IR and NMR spectral investigations were canied out to throw light on the nature of bonding between the two components forming the addition compound.U. S . RAI et SANTHI GEORGE. Can. J. Chem. 70, 2869 (1992.Faisant appel a la mCthode de fusion, on a determine les diagrammes de phase du systkme organique binaire benzidine/pyrogallol. En mesurant le mouvement de croissance du front dans la capillaire, on a CtudiC le comportement lors de leur solidification des composants purs, de leurs eutectiques et de leur composC d'addition. En se basant sur des Ctudes thermiques, microscopiques et de diffraction des rayons X, on peut dCduire que les eutectiques ne sont pas de simples melanges des composants impliquCs. Des etudes par spectroscopies IR et RMN ont CtC entreprises afin de faire la lumikre sur la nature des liaisons entre les deux composants formant le composC d'addition.[Traduit par la rCdaction]

Benzidine-m. aminophenol system gives a double simple eutectic type phase-diagram showing the formation of a 1 : 2 addition compound with congruent melting point surrounded by two eutectics on either side. The linear velocity of crystallization data on pure components, eutectics, and addition compound suggest square relationship between growth velocity and undercooling. From the X-ray diffraction studies it can be inferred that the eutectics are not a simple mechanical mixtures of two components. Whereas microstructural investigations suggest faceted growth of the addition compound and a typical characteristic growth of the eutectics, spectral studies indicate the formation of intermolecular hydrogen bonding between two components forming the molecular complex.In the recent past, the chemistry of eutectics (SINGH, DWIVEDI) and addition compounds (RASTOGI et al. 1981a) has witnessed immense activity due to their unusual physical properties not normally shown by the parent components. Metallic eutectics (ELLIOTT) and intermetallic compounds (COCH) constitute an interesting area of investigation in metallurgy and materials science and much have been added to their knowledge. Due to low transformation temperature, ease in purification, transparency, minimised convection effects and wider choice of materials, direct observation on solidification of transparent organic systems (GLICKSMAN et al.; GRUGEL, HELLAWELL; PIGON, KRAJEWSKA; PODOLINSKY et al.) has been the most useful technique for unravelling the mysteries of solidification. At present these systems have received much importance in material and metallurgical sciences and are being used as metallic alloy models for detailed investigation of the parameters which control solidification. Eutectics, in which parent components have low entropy of fusion simulate the metallic solidification and have been studied (JACKSON, HUNT) in detail.Faceted-non-faceted organic eutectics are chosen as analogues of A1 -Si type systems and much have been studied (FISHER, KURTZ;SLOAN, MCGHIE; SINGH et al. 1985) about them. Faceted-faceted eutectics which are of great importance to carry out the unusual reaction (RASTOGI, SINGH) are the least studied. Several organic reactions which occur at very high temperature and are not possible in ordinary conditions, have been successfully carried out in eutectic media. Because of -OH and -NH, groups and low melting points, benzidine-maminophenol eutectics are very useful for these reactions. In the present paper the results on phase-diagram, microstructure, linear velocity of crystallization, X-ray diffraction and spectral behaviour of benzidine (BZ) -m-aminophenol (mAP) system have been reported.