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.     

Transferability of fragmental contributions to the octanol/water partition coefficient: an NDDO-based MST study

This study examines the transferability of fragmental contributions to the octanol/water partition coefficient. As a previous step, we report the parameterization of the AM1 and PM3 versions of the MST model for n-octanol. The final AM1 and PM3 MST models reproduce the experimental free energy of solvation and the octanol/water partition coefficient (log P(ow)) with a root-mean-square deviation of around 0.7 kcal/mol and 0.5 (in units of log P), respectively. Based on this parameterization, an NNDO-based procedure is presented to dissect the free energy of transfer between octanol and water in contributions directly associated with specific atoms or functional groups. The application of this procedure to a set of representative molecular systems illustrates the dependence of the log P(ow) fragmental contribution due to electronic, hydrogen bonding, and steric effects, which cannot be easily accounted for in simple additive-based empirical schemes. The results point out the potential use of theoretical methods to refine the fragmental contributions in empirical methods.     

Predicting octanol/water partition coefficients using molecular simulation for the SAMPL7 challenge: comparing the use of neat and water saturated 1-octanol

Journal of Computer-Aided Molecular Design - Blind predictions of octanol/water partition coefficients at 298.15 K for 22 drug-like compounds were made for the SAMPL7 challenge. The octanol/water...     

Predicting octanol/water partition coefficients for the SAMPL6 challenge using the SM12, SM8, and SMD solvation models

Journal of Computer-Aided Molecular Design - Blind predictions of octanol/water partition coefficients at 298 K for 11 kinase inhibitor fragment like compounds were made for the SAMPL6 challenge....     

Predicting octanol/water partition coefficients and pKa for the SAMPL7 challenge using the SM12, SM8 and SMD solvation models

Journal of Computer-Aided Molecular Design - Blind predictions of octanol/water partition coefficients and pKa at 298.15 K for 22 drug-like compounds were made for the SAMPL7 challenge....     

A rapid determination method of the air/water partition coefficient and its application

The air/water partition coefficient (K_aw) and Henry's constant (H) were measured by our own modified EPICS (Equilibrium Partitioning in Closed System) method, which uses two bubble columns. This method gives accurate K_aw data much more rapidly than other methods. In order to establish this method, the influence of airflow rate and the volume ratios of water in two columns to partition coefficient were carefully examined. Then we have measured K_aw for some n-alkanes, aromatic and chlorinated compounds. The experimental results of our modified EPICS method agreed very well with literature values. Besides the relationships between K_aw and molar volume, vapor pressure and water solubility were also analyzed.     

Octane numbers (ONs) of hydrocarbons: a QSPR study using optimal topological indices for the topological equivalents of the ONs

A new method proposed for solving QSPR tasks is based on transition from numerical values to topological equivalents (TEs) of physicochemical properties of chemical compounds. The TEs are unambiguously related to corresponding properties; for n-alkanes, they are linear functions of the number, n, of carbon atoms. Since the TE depends only on the corresponding physicochemical parameter, it can be calculated for any hydrocarbon using the same relationships as those known for n-alkanes. The optimal topological index (OTI) constructed using the chemical structure matrix for TEs usually has a much smaller basis compared to the topological index obtained by analogous procedure for the physicochemical property. An algorithm for modeling of physicochemical properties using the TEs was developed and evaluated taking the octane numbers of alkanes and cycloalkanes as examples. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1619–1631, September, 2007.     

Electrochemical bromination of cyclic and acyclic enes using biphasic electrolysis

A simple method of electrochemical bromination of a series of cyclic and acyclic enes (styrene and substituted styrenes, stilbene, indene, and cyclooctene) in a biphasic water–chloroform mixture mediated by bromide/bromine redox system is reported. Aqueous 25% NaBr/H₂SO₄ is used as the electrolyte. Regio- and stereoselective dibromination of enes is achieved. Moderate to excellent yields of the product (83–98%) is obtained depending on the substrate. Electrolyte reuse has also been demonstrated successfully using HBr in the dibromination of styrene.     

Determination of air-loop volume and radon partition coefficient for measuring radon in water sample

A simple method for the direct determination of the air-loop volume in a RAD7 system as well as the radon partition coefficient was developed allowing for an accurate measurement of the radon activity in any type of water. The air-loop volume may be measured directly using an external radon source and an empty bottle with a precisely measured volume. The partition coefficient and activity of radon in the water sample may then be determined via the RAD7 using the determined air-loop volume. Activity ratios instead of absolute activities were used to measure the air-loop volume and the radon partition coefficient. In order to verify this approach, we measured the radon partition coefficient in deionized water in the temperature range of 10–30 °C and compared the values to those calculated from the well-known Weigel equation. The results were within 5 % variance throughout the temperature range. We also applied the approach for measurement of the radon partition coefficient in synthetic saline water (0–75 ppt salinity) as well as tap water. The radon activity of the tap water sample was determined by this method as well as the standard RAD-H₂O and BigBottle RAD-H₂O. The results have shown good agreement between this method and the standard methods.