Thermodynamic properties of organic compounds (original) (raw)
Some thermophysical properties of several solid aldehydes
Journal of Thermal Analysis and Calorimetry, 2008
The present study reports a differential scanning calorimetry (DSC) study of the solid aldehydes: 4-hydroxybenzaldehyde [123-08-0] 1; 4-hydroxy-3-methoxybenzaldehyde (vanillin) [121-33-5] 2; 3-ethoxy-4-hydroxybenzaldehyde (ethyl vanillin) [121-32-4] 3; 3,4-dimethoxybenzaldehyde (veratraldehyde) [120-14-9] 4 and 4-methoxycinnamaldehyde [1963-36-6] 5, in the temperature interval from T=268 K to their respective melting temperatures. Temperatures, enthalpies and entropies of fusion and the heat capacities of the compounds as a function of temperature are reported.
Molecules
A universally applicable method for the prediction of the isobaric heat capacities of the liquid and solid phase of molecules at 298.15 K is presented, derived from their “true” volume. The molecules’ “true” volume in A3 is calculated on the basis of their geometry-optimized structure and the Van-der-Waals radii of their constituting atoms by means of a fast numerical algorithm. Good linear correlations of the “true” volume of a large number of compounds encompassing all classes and sizes with their experimental liquid and solid heat capacities over a large range have been found, although noticeably distorted by intermolecular hydrogen-bond effects. To account for these effects, the total amount of 1303 compounds with known experimental liquid heat capacities has been subdivided into three subsets consisting of 1102 hydroxy-group-free compounds, 164 monoalcohols/monoacids, and 36 polyalcohols/polyacids. The standard deviations for Cp(liq,298) were 20.7 J/mol/K for the OH-free compun...
Solid state and sub-cooled liquid vapour pressures of cyclic aliphatic dicarboxylic acids
Atmospheric Chemistry and Physics Discussions, 2010
Knudsen Effusion Mass Spectrometry (KEMS) has been used to measure for the first time the solid state vapour pressures of a series of aliphatic cyclic dicarboxylic acids with increasing ring size. Additionally the atmospherically important compounds; cis-pinonic acid and levoglucosan were also measured. Differential Scanning Calorimetry (DSC) was used to measure melting points, enthalpies and entropies of fusion, which were used to determine sub-cooled liquid vapour pressures for the compounds. The sub-cooled liquid vapour pressure of straight chain, branched and cyclic dicarboxylic acids was compared to a selection of estimation methods.
Thermodynamic Properties of Organic Acids and Some Their Derivatives
IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA, 2019
The heats of vaporization, combustion, formation, entropy and the heat capacities in different phases of different carbonic acids and their derivatives: acetates, esters with fatty radicals, two-, three- and four-basic acids (52 compounds) were analysed in the framework of one-parametric mathematic equations. The experimental data of all chosen one-, two-, three- and four-basic acids were analyzed. It was determined, that all thermodynamic functions of these types of compounds depend on the number of valence electrons N, from which the sum of lone electron pairs g as represented in the equations Δvap,c,fH° = i ± f (N-g) and S°(Cp) = i ± f (N-g) is excluded. The coefficients f in the first equations is in the range of 104-113 kJ mol-1 electron-1, that corresponds to the same values f in the equations, which are mentioned in our earlier papers on the determination of the heats of combustion of organic acids. As concerned of coefficient i in the received equations, necessary to note ...
Molecules, 2020
The calculation of the isobaric heat capacities of the liquid and solid phase of molecules at 298.15 K is presented, applying a universal computer algorithm based on the atom-groups additivity method, using refined atom groups. The atom groups are defined as the molecules' constituting atoms and their immediate neighbourhood. In addition, the hydroxy group of alcohols are further subdivided to take account of the different intermolecular interactions of primary, secondary, and tertiary alcohols. The evaluation of the groups' contributions has been carried out by solving a matrix of simultaneous linear equations by means of the iterative Gauss-Seidel balancing calculus using experimental data from literature. Plausibility has been tested immediately after each fitting calculation using a 10-fold cross-validation procedure. For the heat capacity of liquids, the respective goodness of fit of the direct (r 2) and the cross-validation calculations (q 2) of 0.998 and 0.9975, and the respective standard deviations of 8.24 and 9.19 J/mol/K, together with a mean absolute percentage deviation (MAPD) of 2.66%, based on the experimental data of 1111 compounds, proves the excellent predictive applicability of the present method. The statistical values for the heat capacity of solids are only slightly inferior: for r 2 and q 2 , the respective values are 0.9915 and 0.9874, the respective standard deviations are 12.21 and 14.23 J/mol/K, and the MAPD is 4.74%, based on 734 solids. The predicted heat capacities for a series of liquid and solid compounds have been directly compared to those received by a complementary method based on the "true" molecular volume and their deviations have been elucidated.
Estimating Solid–Liquid Phase Change Enthalpies and Entropies
Journal of Physical and Chemical Reference Data, 1999
A group additivity method based on molecular structure is described that can be used to estimate solid-liquid total phase change entropy (⌬ 0 T fus S tpce) and enthalpy (⌬ 0 T fus H tpce) of organic molecules. The estimation of these phase changes is described and numerous examples are provided to guide the user in evaluating these properties for a broad range of organic structures. A total of 1858 compounds were used in deriving the group values and these values are tested on a database of 260 additional compounds. The absolute average and relative errors between experimental and calculated values for these 1858 compounds are 9.9 J•mol Ϫ1 •K Ϫ1 and 3.52 kJ•mol Ϫ1 , and 0.154 and 0.17 for ⌬ 0 T fus S tpce and ⌬ 0 T fus H tpce , respectively. For the 260 test compounds, standard deviations of Ϯ13.0 J•mol Ϫ1 •K Ϫ1 (⌬ 0 T fus S tpce) and Ϯ4.88 kJ mol Ϫ1 (⌬ 0 T fus H tpce) between experimental and calculated values were obtained. Estimations are provided for both databases. Fusion enthalpies for some additional compounds not included in the statistics are also included in the tabulation.
Thermophysical properties of n-Alkanes from C1 to C20 and their prediction for higher ones
Fluid Phase Equilibria, 1990
Reliable values for the thermophysical properties: critical properties, acentric factors, vapor pressures (P'), saturated liquid volumes (Vs) and enthalpies of vaporization (AR") for the C1 to Czo n-Alkanes are presented. The Ps. Vs and AH" values are successfully predicted with a translated form of the van der Waals (t-vdW) and of the Peng-Robinson (t-PR) equation of state (EoS) presented here.
Thermoanalytical investigations on heterocyclic organic compounds
Thermochimica Acta, 1989
acids are readily obtained from the reaction between phthalic auhydride and substituted aniline. The thermal decomposition reactions of these acids were studied under an inert atmosphere using dynamic thermogra~met~ and differenti~ scanning calorimetry. The acids decomposed directly into the corresponding oxazine derivatives. No dehydra~on reaction could be detected and consequently there was no chance for the formation of imides or isoimides to take place. Practical mechanistic steps are postulated in order to explain the formation of decomposition products during thermal treatment. The effects of various substituents on the mode of decomposition as well as on the thermal stability of the acids were also studied.
Journal of Chemical & Engineering Data, 2020
This paper reports liquid heat capacity data on members of the linear saturated dicarboxylic acid family and one dicarboxylic acid derivative measured using modulated differential scanning calorimetry. The dicarboxylic acids range in carbon number from 4 to 14. The compounds studied are dimethyl oxalate (CAS RN 553-90-2), adipic acid (1,6-hexanedioic acid, CAS RN 124-04-9), pimelic acid (1,7-heptanedioic acid, CAS RN 111-16-0), suberic acid (1,8-octanedioic acid, CAS RN 505-48-6), azelaic acid (1,9-nonanedioic acid, CAS RN 123-99-9), sebacic acid (1,10-decanedioic acid, CAS RN 111-20-6), dodecanedioic acid (1,12-dodecanedioc acid, CAS RN 693-23-2), and tetradecanedioic acid (1,14-tetradecandioic acid, CAS RN 821-38-5). The experimental results show a consistent family trend and are compared to prediction methods and data from other chemical families. A discussion of the differences in liquid heat capacity between carboxylic acids, n-alkanes, and dicarboxylic acids is presented, the accuracy of prediction through thermodynamic equations is analyzed for the family, and a correction factor for the Ruzicka−Domalski prediction method (