Enthalpies of sublimation and vaporization of poly-substituted phenols containing intramolecular hydrogen bonds by solution calorimetry method

© 2020 Elsevier B.V. A simple procedure for calculation of solvation enthalpy of compounds containing intramolecular hydrogen bond was developed. This procedure is based on the assumption that fragments of molecules containing intramolecular hydrogen bonds can be express as one group contribution. The proposed approach was verified by determination of the vaporization/sublimation enthalpies of poly-substituted phenols. Vaporization/sublimation enthalpies were obtained as difference between solution and solvation enthalpies in benzene. Solution enthalpies of thirteen compounds in benzene were measured in the present study. The obtained vaporization/sublimation enthalpies are in good agreement with values available in the literature. This promising result makes the solution calorimetry method preferable for quick estimations of enthalpy of phase transition, especially for explosive or compounds of low volatility

Additivity of vaporization enthalpy: Group and molecular contributions exemplified by alkylaromatic compounds and their derivatives

Recently we proposed a system of methods for evaluation of the phase transition enthalpies of aromatic and heteroaromatic compounds, on the one hand, and aliphatic compounds, on the other. The present work is aimed at the prediction of the vaporization enthalpies of alkylaromatic compounds and their derivatives. According to the proposed approach, the vaporization enthalpy of an aliphatic compound carrying aromatic substituents can be derived from the vaporization enthalpy of an aliphatic compound, serving as a backbone, and a contribution of an aromatic fragment, which is also derived from the vaporization enthalpy of a pure aromatic compound. The additivity of the vaporization enthalpies of the fragments may fail if their combination is followed by the changes in (1) polarizability due to π-conjugation and (2) intermolecular hydrogen bonding strength. Independent procedures for accounting for both factors were proposed. The vaporization enthalpies of 174 compounds at 298.15 K were calculated and compared with the literature values. The average deviation and root-mean-square deviation were –0.2 and 1.5 kJ·mol−1, respectively, being competitive with the accuracy of experimental techniques

Vaporization/sublimation enthalpies of mono- and dimethyl-esters estimated by solution calorimetry method

© 2020 Elsevier B.V. The additive scheme for calculating the solvation enthalpies of aliphatic compounds has been developed for linear mono- and dimethyl-esters. Ester group contribution to the enthalpy of solvation in n-heptane was obtained. Accuracy of the proposed approach for determination of solvation enthalpies of linear mono- and dimethyl-esters was tested by comparison with experimental solvation enthalpies. In most cases, deviations do not exceed 1 kJ·mol−1. It was found that the dependence of the solution enthalpies of mono- and dimethyl-esters on the number of carbon atoms in the molecule can be fitted by power function. This dependence and a group-additivity scheme for solvation enthalpy were used for estimation of the enthalpies of phase transitions of mono- and dimethyl-esters. Evaluated values of sublimation, vaporization, and fusion enthalpies at 298.15 K are in good agreement with experimental data obtained by conventional methods

Thermochemical properties of pyrazine derivatives as seminal liquid organic hydrogen carriers for hydrogen storage

This work contributes to our primary interest in applications of experimental and computational thermochemistry methods for providing the basic data required in chemical-process design. Pyrazine derivatives are considered as a seminal liquid organic hydrogen carriers. The standard molar enthalpies of vaporisation/sublimation of pyrazine derivatives were derived from the vapour pressure temperature dependences measured by the static and transpiration method. Enthalpies of fusion of the solid compounds were measured using DSC. Thermodynamic data on solid–gas, liquid–gas, and solid–liquid phase transitions available in the literature were collected and combined with own experimental results. We have evaluated and recommended the set of vaporisation and formation enthalpies of pyrazine derivatives at 298.15 K as the reliable benchmark properties for further thermochemical calculations. Gas phase molar enthalpies of formation of pyrazine derivatives calculated by the high-level quantum-chemical method G4 were in agreement with the recommended experimental data. Compilation of experimental and theoretical results derived in this work is useful for optimisation of hydrogenation/dehydrogenation reactions involved in the hydrogen storage technologies

Application of the Flash DSC 1 and 2+ for vapor pressure determination above solids and liquids

In this work, we adapted a procedure for vapor pressures determination utilizing a fast scanning chip calorimeter to the case of a stagnant gas phase. The validity of the developed procedure was checked by comparing the vapor pressures determined in this work for several polyaromatic, heteroaromatic, and long-chain compounds with reliable vapor pressure data available in the literature. The results of the comparison show that the commercial Flash DSC 1 and the Flash DSC 2+ (Mettler Toledo, Switzerland) can be used for a reliable appraisal of the vapor pressures in a wide temperature range, which allows using these devices without additional technical changes as a source of comprehensive and internally consistent information about the energy of phase transitions

Long-chain linear alcohols: Reconciliation of phase transition enthalpies

© 2020 Elsevier Ltd Thermodynamics of phase transitions of long-chain linear alcohols were revised by means of complementary experimental techniques: transpiration, differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and solution calorimetry (SC). Absolute vapor pressure temperature dependencies for heptadecanol-1 and octadecanol-1 were measured by the transpiration and FSC methods. The validity and accuracy of the FSC experimental setup towards reliable vapor pressure measurement was established. It was shown that vaporization enthalpies for heptadecanol-1 and octadecanol-1 obtained by FSC and transpiration method are in good agreement. The SC approach was used for estimation of sublimation/vaporization enthalpies of linear alcohols. Energetics of the phase transitions found with the SC-approach agree well with that from conventional methods and they are consistent with each other

A rational synthetic approach for producing quaternary ammonium halides and physical properties of the room temperature ionic liquids obtained by this way

In the present paper the rational strategy for the high-yield solvent free synthesis of alkylammonium halides which consists in the nucleophilic addition of alkylaminoethanols to 2-chloroethanol was described. The proposed strategy was used to synthesize hydroxyl-functionalized solid ionic compounds such as dimethyl (or methyl) di-(tri)(2-hydroxyethyl) ammonium chloride and tetra-(2-hydroxyethyl) ammonium chloride, as well as novel room temperature ionic liquids (RTILs) such as dimethyl (IL-4) and methyl mono-(di-)(2-hydroxyethyl) (2-hydroxyethoxy)ethyl chloride (IL-5) all of which were characterized by FT-IR, 1H and 13C NMR. For the newly obtained RTILs, density (ρ) and viscosity (η) were obtained at temperatures from T = (283.15 to 353.15) K while the refractive index (nD) was measured from T = (283.15 to 343.15) K. The data on ρ and nD were used for calculation of the RTILs’ fractional free volumes (FFV), molar refraction, and pseudo-activation energy of viscous flow. In addition, NH3 absorption capacity of the obtained ILs was estimated gravimetrically. It was shown that this property correlates with the IL's FFV and increases by two times for IL-5 which exhibits an additional hydroxyl group compared to IL-4