Sublimate compounds

Vitovec, J., Smolik, J. and Kugler, K. Collect. Czech. Chem. Commun. 43 (1978) 396-400. Separation of sublimable compounds by partial crystallisation from their vapour mixture. 

Sublimation. Such effects can also be seen in solid-gas interphase. Scheme 30 shows the consequences of fractional sublimation of partially resolved L-mandelic acid (47). The optical purity could be enhanced or reduced, depending on the optical purity of the starting material. Since the eutectic point of mandelic acid is obtained with about a 75 25 enantiomer ratio, such a mixture is more readily sublimed than the racemate or conglomerate. Scheme 30 gives other examples of optical enrichment by sublimation. Phenyl 1-phenyl-1-propyl sulfide in 6% ee affords the sublimed compound in 74% ee, but the residue is... 

The alkoxides and phenoxides of boron are all generally readily distillable or sublimable compounds and tend to be monomeric in solution.1 However, the r-butoxide undergoes thermal degradation to produce an alkene, presumably via a carbonium ion intermediate.160... 

The sublimed compound is a crystalline canary-yellow substance the crude product may vary in color from bright to creamy yellow, but since no differences in the analytical data and in i.r. spectrum between the sublimed substance and the crude product are observed, the sublimation is not recommended. Dodecacarbonyltetrairidium is only very slightly soluble in all solvents. A saturated methylene chloride solution shows an i.r. spectrum6 which has bands at 2067 and 2027 cm.-1 (1-cm. cell, Perkin Elmer 621). The i.r. spectrum of the solid (KBr pellets) has bands at 2084, 2053, and 2020 cmf1. The carbonyl is inert to air and water. It reacts with alkali hydroxides and cyanides, most rapidly in methanol or ethanol suspension, as well as with metallic sodium in tetrahydrofuran, giving... 

The pyrolysis of PET by Sakata [3] has been found surprisingly to yield no liquid products. It is widely known that compounds that undergo sublimation, such as tereph-thalic acid and benzoic acid, are produced by the thermal decomposition of PET and this causes problems in plastic pyrolysis plants. Interestingly Yoshioka et al. [4] found that the addition of calcium hydroxide (slaked lime) gives high selectivity for benzene formation without producing sublimation compounds such as terephthalic acid. The yield of benzene is around 35 wt% at 700°C and a 10.0 calcium hydroxide/PET molar ratio. 

Cyclization of organoaluminums proceeds via intermolecular and intramolecular exchange. The bis-hydroalumination product of McjAlC CH, (Me2Al)3CMe, can lose Me3Al leading to a sublimable compound with the composition Me5AlgC4Me4 and an adamantane-like structure ... 

The basic differences between a molecular distillation and a sublimation at low pressures are that (1) the molecular distillation goes from solid to liquid to gas, which usually requires more energy than a sublimation that goes from the solid directly to the gas, and (2) the surface of the subliming compound is continuously renewed by evaporation, convection, or diffusion. As a result, a sublimation in many cases is faster and more economical. 

Figure 7-19, p. 82, shows the components required for a regular sublimation and Figure 7-20, p. 82, shows the components needed for the simplest type of entrainer Figure 7-17. sublimations. compound... 

Hydrolysis of (345) yields a colorless, sublimable compound (CH2)2As404 which has the adamantane structure (34. Reaction with H2S yields (347) which is insoluble in all common organic solvents, and so no structure proof has yet been possible. With methylamine or methyl-(bistrimethylsilyl)amine (345) reacts to give the 2,4,6,8-tetramethyl-2,4,6,8-tetraaza-l,3,5,7-tetra-arsaadamantane (348 R = Me) (Scheme 64) <70ZAAC(377)120>. Several other A-substituted derivatives of (348) have been described <75JOM(94)393>. 

It is recommended to scan the DSC under the proposed experimental conditions to check the curvature and noise level of the instrument baseline before analysing samples. There are several reasons why the instrument baseline may be curved and/or display a high noise level. Trace amounts of residue from a previous experiment may be attached to the sample holder. Decomposed or sublimated compounds frequently condense on the sample holder, distorting the shape and quality of the instrument baseline. If the instrument baseline is still not satisfactory, following cleaning with ethanol or acetone, there may be a problem with the purge gas flow. The linearity of the instrument baseline will be... 

The behavior of the cyclic compound ( 128 — 13)3 can be explained by considering the reaction temperature and the amount of LiAlH used. Table 30 gives an account of the reaction conditions, as well as an indication of the volatile and sublimable compounds produced. 

A small lichen sample is introduced into a mass spectrometer by a direct inlet system. The sample is heated, and many lichen substances sublime readily at the very low pressure (about 10 torr) in the mass spectrometer. Mass spectra of the subliming compounds may then be recorded and used for tentative identification. (For a general introduction to mass spectrometry, see Beynon et al, 1968). 

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