Melting points phase diagrams

Silicon is soluble in aluminum in the solid state to a maximum of 1.62 wt % at 577°C (2). It is soluble in silver, gold, and 2inc at temperatures above their melting points. Phase diagrams of systems containing silicides are available (2,3). 

Fig. 8 Melting point phase diagram obtained for the /V-acetyl analogue of methyldopa, which exhibits typical racemate behavior.

Another way of ensuring that a glass surface is free of water or hydroxyl groups is to cover it with a film of sodium. This method was used when the melting point phase diagram for the system isobutene + titanium tetrachloride was determined (Longworth, Plesch and Rutherford, 1959 Plesch, 1972), but it cannot be used on silane-treated glass as the sodium will not spread on the waxy surface. 

Solubility of racemic praziquantel was determined in MeOH and 2-PrOH in the temperature range between 0 °C and 40 °C. A ternary phase diagram of praziquantel enantiomers and the MeOH system was also determined (06CH259). The solubility phase and binary melting-point phase diagrams were determined. Experimental and predicted aqueous solubility of praziquantel was reported (07CPB669,08SQE191). Dissolution of praziquantel... 

Figure 1. A racemic conglomerate (a) the principle of Preferential Crystallization, (b) a packing mode of enantiomers in the crystal with Z = 2, and (c) a representative binary melting-point phase diagram.

Unique Binary Melting Point Phase Diagram... 

To discuss the crystalline nature of the compounds showing Preferential Enrichment, two kinds of unique binary melting-point phase diagrams obtained actually for two typical compounds, NNMe3 and NBMe3, deserve attention. 

Figure 7. Binary melting-point phase diagram of NNMe3. White and black circles represent the temperatures of the beginning and the end of fusion, respectively. (Reprinted with permission from ref 18. Copyright 2003 American Chemical Society.)...

Conglomerates and racemates can be easily distinguished from each other on the basis of their melting point phase diagrams [25]. A conglomerate system will exhibit a single eutectic minimum in its phase diagram at the mole fraction of 0.5, since at this enantiomeric ratio the system will consist of an equimolar mixture of two crystalline enantiomers that melts as if it were a pure system. Qn the other hand, a racemate system will exhibit two eutectics on either side of the mole fraction of 0.5 since both enantiomers will be foimd in the unit cells of the crystallized solid. 

An example of the type of melting point phase diagram that is typical for a conglomerate system is shown in Fig. 9.2, which illustrates the phase diagram reported for methyl diacetyltartrate [32]. Below the eutectic temperature of 79 °C, the system will exist as a mixture of solid D-enantiomer and L-enantiomer. At the exact composition of the racemic mixture (X = 0.5), the system will exist entirely in the liquid phase above the eutectic temperature. At mole fractions where the amount of (L)-enantiomer exceeds that of the (D)-enantiomer, the system will exist as an equilibrium mixture of racemic liquid and solid (L)-enantiomer. 

Care must be observed in the interpretation of a melting point phase diagram for those instances where the eutectic temperatures are located close to the equimolar composition, as such systems could be erroneously interpreted as indicating the existence of a conglomerate system. An example of this type of behavior is shovm in Fig. 9.6 for the ethyl diace-tyltartrate system, where a eutectic temperature of 42 °C was found for a d-enantiomer composition of 55.7 mole-percent [32]. On the other hand, when the eutectic temperatures are close to the melting points of the pure enantiomers, the phase diagram could be mistaken for that of a solid solution. An example of this behavior is shovm in Fig. 9.7 for the methyl dibenzoyltartrate system, where a eutectic temperature of 130.4 °C was... 

FIGURE 9.9 Melting point phase diagram obtained for the salt formed between racemic ibuprofen and the (S)-enantiomer of a-methylbenzylamine [H.G. Brittain, unpublished results]. 

Neah, S.H. Shinwari, M.K. Hellmuth, E.W. Melting point phase diagrams of free base and hydrochloride salts of bevantolol, pindolol and propanolol. Int. J. Pharm. 1993, 99, 303-310. 

Thus, melting points (even in the absence of a full melting point phase diagram) and X-ray powder diffraction patterns are useful criteria for assessing the results of such crystallizations if suitable single crystals are formed, the more elaborate (but far more informative in terms of structural detail) method of single-crystal structure determination provides more definitive confirmation and structural descriptions of phase identities. 

The molecular chirality associated with an optically active molecule is ordinarily manifested in the crystallography of the compound [1], Since the historical development of optical activity was greatly aided by systematic studies of the habits of enantiomorphic crystals, the concepts of molecular dissymmetry, crystallography, and chirality are inexorably linked. As with any other solid, these materials can be characterized on the basis of their crystal structures and through an understanding of their melting point phase diagrams. 

Since conglomerate systems consist of totally independently formed enantiomer crystals and are therefore mere physical mixtures of the enantiomer components, these constitute a binary system. Such binary mixtures are easily described by the phase rule and can be profitably characterized by their melting point phase diagrams [10]. Since the components of a conglomerate racemate will melt indepen-... 

Portion of the melting point phase diagram obtained for the crystalline conglomerate formed by 4,4 -dimethyl-8,9,10-trinor-spiro-2,2 -bomane. 

In addition to melting point phase diagrams, ternary solubility phase diagrams, in which the third compound is a liquid solvent, may also be applied to classify racemates (Fig. 6) at constant temperature. 

Figure 21.2.6. Melting point phase diagram for [C -mim][PFJ ionic liquids as a fimction of alkyl chain length n showing the melting transitions from crystalline (closed square) and glassy (open square) materials and the clearing transition (circle) of the liquid crystalline (LC) terms.

The solid-state properties of propranolol hydrochloride in respect of the relationship between the racemic mixture and (S) - enantiomer have been previously reported [25]. The shape of a ternary phase diagram can theoretically be deduced from respective binary phase diagram. Similar to the results of the binary melting point phase diagram, ternary phase diagram shows a shape of a typical conglomerate type compound [25]. However, the two eutectic points are so close to each other that the exaet position of euteetie points is not likely to be determined precisely. 

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