Melts complex formation

Although the boiling point of SbCl3 is 219°C, the vapour pressure of the melt corresponding to the above composition is only about 600 Pa, indicating complex formation. 

Rate of complex formation between chiral alcohols and DBTA monohydrate in hexane suspension is quite slow (see Figure 1) and numerous separation steps are necessarry for isolation of the alcohol isomers (filtration of the diastereoisomeric complex then concentration of the solution, decomposition of the complex, separation of the resolving agent and the enantiomer, distillation of the product). To avoid these problems, alternative methods have been developed for complex forming resolution of secondary alcohols. In a very first example of solid phase one pot resolution [40] the number of separation steps was decreased radically. Another novel method [41] let us to increase the rate of complex forming reaction in melt. Finally, first examples of the application of supercritical fluids for enantiomer separation from a mixture of diastereoisomeric complexes and free enantiomers [42, 43] are discussed in this subchapter. 

Optical resolution of menthol (28) with DBTA in hexane suspension is quite efficient (S = 0.374, Table 5 [38]) but complex formation is slow. In order to increase the reaction rate, the highest possible concentrations of the reactants were reached by solving DBTA monohydrate in the melt of racemic menthol. [41]... 

In the process of lanthanide complex formation with the porphyrins, the ligand loses two protons and yields lanthanide hydroxy porphyrin or lanthanide porphyrin X, where X = C1, Br, NOJ, etc. Many lanthanide complexes with substituted porphyrins have been prepared by heating a mixture of porphyrin and the lanthanide salt in imidazole melt in the range 210-240°C. When the complex formation is complete the solvent (i.e.) imidazole is eliminated by either sublimation [81] or by dissolution of the mixture in benzene, followed by washing with water [82]. Further purification requires column chromatography. The starting material can be anhydrous lanthanide chloride or hydrated lanthanide acetylacetonate. After purification the final product tends to be a monohydroxy lanthanide porphyrin complex. 

Copper(I) chloride and bromide are made by boiling an acidic solution of the Cu" salt with an excess of Cu on dilution, white CuCl or pale yellow CuBr is precipitated. Addition of I- to a solution of Cu2+ forms a precipitate that rapidly and quantitatively decomposes to Cul and iodine. Copper(I) fluoride is unknown. The halides have the zinc blende structure (tetrahedrally coordinated Cu+). Cop-per(I) chloride and CuBr are polymeric in the vapor state, and for CuCl the principal species appears to be a six ring of alternating Cu and Cl atoms with Cu—Cl, —2.16 A. White CuCl becomes deep blue at 178°C and melts to a deep green liquid. The halides are very insoluble in water but are solubilized by complex formation... 

Zentel R, Wu J, Cantow HJ. (1985) Influence of electron-donor-acceptor complex formation on the melt viscosity of some poly(dimethylsiloxane)s. Makromol. Chem. 186 1763-1772. 

The complexes obtained with simple monoolefins (305, 438, 486) are crystalline, yellowish-brown compounds, melting with decomposition below 100°C. Complex formation results in a shift to lower frequencies of the infrared C=C stretching vibration by about 100-150 cm (261, 438, 478). The molecular structure most commonly encountered in these complexes is the bridged dimer (198). The far-infrared spectrum of the ethylene complex dimer has a band at 427 cm assigned to the Pt-C2H4 stretching vibration (261). 

Among the pentavalent elements, the most important are niobium and tantalum. Niobium is an excellent material for surface treatment of steel materials for chemical industry due to its high hardness and corrosion-resistance in wet acidic conditions. Nowadays, niobium is also used for the preparation of superconductor tapes and it is used in other branches of industry, for instance in nuclear technology and metallurgy. Tantalum is also of similar importance. For these applications, it is necessary to prepare high purity metal. Molten salt electrolysis, as an alternative process to classical thermal reduction, provides niobium and tantalum with required quality. In order to optimize these processes, it is necessary to know details of both complex formation and redox chemistry of the species present in the melts. 

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