Normal and limiting points on the boiling curves

The possibility of describing the curves of boiling on the results of studies conducted only at normal pressure, as well as of the existence of gas-liquid systems with the parameters above the critical point parameters.     

Determination of boiling points on the Kofler stage

Summary A method for determining boiling points on theKofler stage is described. The sample is sealed in a glass capillary with a drop of mercury and observed under the microscope during the heating operation. Boiling ranges may be obtained on complex materials.

---

Zusammenfassung Ein Verfahren zur Bestimmung des Siedepunktes mit einigen Mikrogrammen von Flüssigkeit wird beschrieben. Das Tröpfchen wird mit Hilfe eines Tropfens Quecksilber in einer Glaskapillare eingeschlossen, wie es aus Abb. 1 ersichtlich ist, und während des Erhitzens amKofler-Heiztisch unter dem Mikroskop beobachtet. Reine Substanzen verdampfen innerhalb eines engen Temperaturbereiches. Mit etwa zehnmal größeren Materialmengen ist es möglich, den Siedebereich von komplizierten Mischungen zu studieren.

---

Résumé On décrit un procédé pour la détermination du point d'ébullition avec quelques microgrammes de liquide. La gouttelette est enfermée au moyen d'une goutte de mercure dans un tube capillaire et observée pendant le chauffage, sous le microscope, à la table chauffante deKofler. Les substances pures s'évaporent dans l'intérieur d'un domaine étroit de température. Il est possible d'étudier le domaine d'ébullition de mélanges compliqués avec des quantités de matière environ 10 fois plus grandes.

---

---

With 2 Figures.     

Structure-related melting and boiling points of inorganic compounds

The paper is aimed at rationalizing relationships between the structure of inorganic compounds in condensed phases and their melting and boiling points. It is documented that the main factor governing both points is their molecular or polymeric nature. In case of polymeric ionic compounds, the higher actual charge bearing by the ions involved, the higher their melting/boiling points. In case of covalent polymers, the value of both points increases with polymer dimensionality (1D → 2D → 3D polymers) and with the number and energy of the respective covalent bonds. In case of molecular compounds, both points depend on the weight and shape of molecules, the presence of hydrogen bonds, and electric quadrupole moment.     

Thermogravimetric analysis for boiling points and vapour pressure

A TGA instrument has been adapted for rapid measurement of boiling points and vapour pressure at temperatures from ambient up to 400°C and pressures from ambient down to 20 mm Hg. Samples were contained in sealed holders having a laser-drilled aperture. Several organic liquids in the 100 to 300 gMW range showed good agreement with reference vapour pressure data. Sample mass, heating rate, and use of inert diluents were important variables affecting accuracy of vapour pressure measurements.     

Critical temperatures of elements from their boiling points

A linear relation between critical temperature and boiling point is proposed for elements belonging to the same group in the periodic table. The validity of the relationship is demonstrated for the alkalies and the groups 16, 17 and 18. From this the critical temperature of tellurium is predicted as 2325?K and that for polonium as 2277?K.     

Extended molecular connectivity: Prediction of boiling points of alkanes

It is shown that extended molecular connectivity may be used for “structure-property” studies. The statistical parameters of the correlation relations of boiling points with extended molecular connectivity indices found for a sample of alkanes (n = 74) are the following: the best two-parameter correlation r = 0.9948, s = 4.7; the best three-parameter correlation r = 0.9971, s = 3.5. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1154–1159, November–December, 1997.     

Evaluation of the polarity and boiling points of nitrogen-containing heterocyclic compounds by gas chromatography

Experimental gas-chromatographic data for 55 aromatic and aliphatic N-containing heterocyclic compounds and C₅–C₁₃ n-alkanes are analyzed. The polar constitutents of the boiling points (T _pol) were calculated as the difference between the boiling points measured directly and the boiling points calculated from GC data obtained on a nonpolar column. Depending on the number, nature, and position of heteroatoms and alkyl groups in the rings and the structures of the molecules, theT _pol values vary from −11° to +82°. The possibility of usingT _pol values to estimate the physicochemical properties of compounds is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp., 323–326, February, 2000.     

计算环烷烃沸点的新方法——基团键贡献法

根据分子中基团的特性和连接性，发展了一种直接根据分子结构信息计算环烷 烃沸点的新方法——基团键贡献法，该方法既考虑分子中基团的特性，又考虑基团 之间的连接性（化学键），具有基团贡献法和化学键贡献法的特点。对256种环烷 烃沸点的计算结果表明，计算值与实验值的一致性令人满意，平均误差0.71。     

改进的连接性指数用于链烷烃热力学性质与沸点研究

基于邻接矩阵和原子特征值qi，建立邻接指数^mQ,用^0Qr,^1Q与85种链烷烃的标准生成焓、标准生成自由能、标准熵和沸点关联，相关系数均在0.99以上，属于良好模型，与Randic指数的^mX比较，^mQ具有良好的性质相关性。     

Estimation of normal boiling points of hydrocarbons from descriptors of molecular structure

Correlations for estimation of thermophysical properties are needed for the design of processes and equipment related to phase equilibria. The normal boiling point (NBP) is a fundamental characteristic of chemical compounds, involved in many correlations used to estimate important properties. Modern simulation packages usually require the NBP and a standard liquid density from which they can estimate all other necessary properties and begin the design of particular processes, installations and flowsheets. The present work contributes a correlation between the molecular structure and the normal boiling point of hydrocarbons. Its main features are the relative simplicity, sound predictions, and applicability to diversified industrially important structures, whose boiling points and numbers of carbon atoms span a wide range. An achievement of particular interest is the opportunity revealed, for reducing the number of the compounds required for the derivation (the learning set), through multivariate analysis and molecular design. The high accuracy achieved by the correlation opens up a possibility for systematic studies of chemical engineering applications in which the effects of small changes are important. This also defines a path towards the more general problem of the influence of uncertainties in calculated thermophysical parameters on the final outcome of computer aided simulation and design.