Ebulliometric

Silva, A.M., and L. A. Weber, "Ebulliometric Measurement of the Vapor Pressure of 1-Chloro-l,l-Difluoroethane and 1,1-Difluoro Ethane, J. Chem. Eng. Data, 38, 644-646 (1993). 

Although calorimetric methods are usually regarded as yielding the most accurate enthalpies of vaporization [39], the measurement of the saturation vapor pressures of a liquid as a function of temperature is also widely used for the same purpose and may afford good quality data. Among these so-called vapor pressure methods [35], differential ebulliometry is probably one of the most reliable. Briefly, the ebulliometric method consists in measuring the boiling temperatures of a liquid at different pressures. In the differential set-up, the pressure over the... 

Figure 2.4 Vapor pressures of ethanol in the 309-343 K temperature range, obtained by an ebulliometric technique [40],...

The compounds Ln(C5H5)2Cl also have been made only with the lanthanides above samarium (772). These compounds are stable in the absence of air and moisture, sublime near 200 °C, are insoluble in non-polar solvents, and exhibit room temperature magnetic moments near the free ion values (772, 113). The chloride ion may be replaced by a variety of anions including methoxide, phenoxide, amide and carboxylate. Some of these derivatives are considerably more air-stable than the chloride — the phenoxide is reported to be stable for days in dry air. Despite their apparent stability, little is known about the physical properties of these materials. The methyl-substituted cyclopentadiene complexes are much more soluble in non-polar solvents than the unsubstituted species. Ebulliometric measurements on the bis(methylcyclopentadienyl)lanthanide(III) chlorides indicated the complexes are dimeric in non-coordinating solvents (772). A structmre analysis of the ytterbium member of this series has been completed (714). The crystal and molecular parameters of this and related complexes are compared in Table 5. 

Several V02+ complexes with (107) and (108) derived from dibenzoylmethane or pyrrole-2-carboxyaldehyde and several amines (taurine, anthranilic acids, /I-alanine) were formulated as [VO(SB)(H2O)2] 780 783 it was proposed that these SBs behave as tridentate ligands and assume a monomeric structure on the basis of fiia and ebulliometric measurements in dioxane. A pyridine adduct [VO(PE)(py)2] was also obtained where PE is the SB (108 R—O = CH2CH2SOj).782... 

The polycarbonates which were used in these experiments had the following molecular weights (determined ebulliometrically) bisphenol I polymer, 20,700 bisphenol II polymer, 54,000 bisphenol A polymer, 28,200. 

In spite of their inefficiency (and even inaccuracy), boiling point (ebulliometric) procedures still are used commonly by small wineries... 

This paper describes an ebulliometric system for routine and special determinations of molecular weights. The system uses a simple ebulliometer, an immersion heater, and a Cottrell-type pump. Temperature sensing is by differential thermopile. Precision varies from about 1 to 6%, and values compare well with those from other laboratories and those from other methods. Values as high as 170,000 have been successfully measured. Some problems encountered in using the ebulliometric method are selection and effect of reference temperature, limitations of the vapor lift pump and a possible substitute for it, measurement of equilibrium concentrations within the operating ebulliometer, and the experimentally determined ebulliometric constant and some factors which influence its value. 

In spite of the apparently successful performance of the ebulliometric system in routine use, a number of variables exist in connection with the operation of the system as it has been described. Many of these variables, as many as possible, are overcome by standardization in routine opera tion. However, they must be recognized if the ebulliometric method is to be understood and applied to special problems. 

The last variable to be discussed is that of the experimentally determined value for the ebulliometric constant, K6. Equation 1 indicates... 

This paper has attempted to show that the ebulliometric method can be used successfully for the routine determination of molecular... 

Weber, L.A. (1992) Ebulliometric measurement of the vapor pressures of R123 and R141b. Fluid Phase Equil. 80, 141-148. 

The continuous curve shown in Fig. 2 was calculated from Eq. (5) by use of the following values for the two parameters K = 11.2 mole-1 liters, k — 41.9 ml. (at 515 mm.) min.-1 mole-1. This dimerization constant is in agreement with the approximate value established by separate ebulliometric experiments. It is clear that within experimental error the data can be fit by an expression of the form of Eq. (5) i.e., the data are consistent with the hypothesis that the active catalyst is a dimer of cuprous acetate. 

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