Thermochemistry of complex salts of transition metal perchlorates with tetrazole ligands

The combined use of combustion and solution calorimetry was proposed as a method for determining the standard enthalpy of formation of the complex salts of transition metals, viz., cobalt(II), nickel(II), and zinc, with the organic ligand (5-aminotetrazol-1-yl)acethydrazide. The enthalpies of solution in water and in a 0.1 M solution of hydrochloric acid were measured for the complex salts and ligand. The enthalpy of combustion of the ligand was determined by the combustion calorimetry method, and its standard enthalpy of formation was calculated. The thermochemical cycle was developed for determining the standard enthalpy of formation of the complex salts. The reliable values of the enthalpies of formation of the salts in the standard states were obtained, and the enthalpies of formation of the earlier unknown complex ions were determined.     

Combined study of thermochemical properties of nitroform and its salts

A combined method for determination of the standard enthalpies of formation of nitroform and its salts was proposed. The enthalpies of dissolution of nitroform and its ammonium, hydrazinium, guanidinium, and potassium salts in water were measured. The enthalpy of combustion of hydrazinium salt of nitroform was determined by a combustion calorimetry, and its standard enthalpy of formation was calculated. The enthalpy of formation of trinitromethyl anion in indefinitely diluted aqueous solution −24.94±0.79 kJ mol⁻¹, was calculated on the basic of the data obtained for enthalpies of formation and dissolution of ammonium and hydrazinium salts of nitroform. Standard enthalpies of formation of nitroform and its salts were calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2451–2454, December, 1998.     

The thermodynamic properties of 1,4-dioxane-2,6-dione

The enthalpies of combustion and formation of 1,4-dioxane-2,6-dione were determined by combustion calorimetry. The transpiration method was used to obtain the temperature dependence of compound vapor pressures and the enthalpies of sublimation and vaporization. Differential scanning calorimetry was used to measure the enthalpy of fusion. Quantum-chemical calculations of the geometric, vibrational, and energy characteristics of the compound were performed, and the enthalpy of formation of the compound in the gas phase was estimated. Statistical thermodynamics methods were used to determine the thermodynamic properties of the compound in the ideal gas state over the temperature range 0–1500 K. Strain energies of some representatives of six-membered cyclic compounds were estimated.     

Experimental and computational thermochemical study of barbituric acids: structure-energy relationship in 1,3-dimethylbarbituric acid

This paper reports an experimental and computational thermochemical study on 1,3-dimethylbarbituric acid. The value of the standard (p° = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by static bomb combustion calorimetry, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K was calculated as -639.6 ± 1.9 kJ·mol(-1). The enthalpy of sublimation was determined using a transference (transpiration) method in a saturated N(2) stream and a value of the enthalpy of sublimation at T = 298.15 K was derived as 92.3 ± 0.6 kJ·mol(-1). From these results a value of -547.3 ± 2.0 kJ·mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical calculations at the G3 and G4 levels were performed, and a study on molecular and electronic structure of the compound has been carried out. Calculated enthalpies of formation are in very good agreement with the experimental value.     

Benchmarking thermochemical experiments and calculations of nitrogen-containing substituted adamantanes

Standard molar enthalpy of formation of 2-cyano-adamantane was obtained by using high-precision combustion calorimetry. The standard molar enthalpies of sublimation of 2-cyano-adamantane and 2,2-dinitro-adamantane at 298.15 K were derived from the vapor pressure temperature dependences measured by transpiration. The molar enthalpies of fusion of these compounds were measured with the help of differential scanning calorimetry. Thermochemical data on functional substituted adamantanes containing nitrogen in the substituents were collected and evaluated. The gas-phase enthalpies of formation were calculated with the high-level quantum-chemical method G4 and compared with the experimental results. The consistent data set of the benchmark quality was suggested for practical thermochemical calculations. Geminal destabilizing effects for the interactions of nitro- and cyano-substituents placed in the second position on the adamantane cage were derived. Structure–property correlations for substituted adamantanes and aliphatic substituted alkanes were found and suggested for the assessment of the gas-phase enthalpies of formation of adamantane derivatives.

     

Ionic liquids. Combination of combustion calorimetry with high-level quantum chemical calculations for deriving vaporization enthalpies

In this work, the molar enthalpies of formation of the ionic liquids [C2MIM][NO3] and [C4MIM][NO3] were measured by means of combustion calorimetry. The molar enthalpy of fusion of [C2MIM][NO3] was measured using differential scanning calorimetry. Ab initio calculations of the enthalpy of formation in the gaseous phase have been performed for the ionic species using the G3MP2 theory. We have used a combination of traditional combustion calorimetry with modern high-level ab initio calculations in order to obtain the molar enthalpies of vaporization of a series of the ionic liquids under study.     

Thermochemical properties of dinitramidic acid salts

Enthalpies of formation and solution of hydrazinium, guanidinium, aminoguanidinium, and triaminoguanidinium salts of nitric and dinitramidic (HN(NO₂)₂, DN) acids were determined by combustion and solution calorimetry methods. Enthalpies of formation of respective cations in infinitely dilute aqueous solution were calculated using the enthalpy of formation of the nitrate ion. The enthalpy of formation of the DN acid anion was determined based on the enthalpy of formation and solution of the acid salts. The weight-average enthalpy of formation of the DN acid anion equal to 8.40±0.13 kcal mol⁻¹ was obtained. The enthalpy of solution of ammonium dinitramide (ADN) was measured (8.71±0.01 kcal mol⁻¹). From these data, the enthalpy of formation of ADN was calculated (−32.14±0.14 kcal mol⁻¹). The energy of combustion of ADN was measured by the calorimetry method, and the enthalpy of formation of ADN was calculated for a sample with purity above 99.9% (−32.20±0.19 kcal mol⁻¹). The weight-average enthalpy of formation of ADN equal to −32.16±0.11 kcal mol⁻¹ is recommended for use. Enthalpies of formation of sodium, potassium, and cesium salts of DN acid were determined.     

Organic carbonates: experiment and ab initio calculations for prediction of thermochemical properties

This work has been undertaken in order to obtain data on thermodynamic properties of organic carbonates and to revise the group-additivity values necessary for predicting their standard enthalpies of formation and enthalpies of vaporization. The standard molar enthalpies of formation of dibenzyl carbonate, tert-butyl phenyl carbonate, and diphenyl carbonate were measured using combustion calorimetry. Molar enthalpies of vaporization of these compounds were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. Molar enthalpy of sublimation of diphenyl carbonate was measured in the same way. Ab initio calculations of molar enthalpies of formation of organic carbonates have been performed using the G3MP2 method, and results are in excellent agreement with the available experiment. Then the group-contribution method has been developed to predict values of the enthalpies of formation and enthalpies of vaporization of organic carbonates.     

Experimental and computational thermochemical study of 2-thiobarbituric acid: structure-energy relationship

This paper reports an experimental and computational thermochemical study on 2-thiobarbituric acid (2-thioxodihydropyrimidine-4,6(1H,5H)-dione), [CAS 504-17-6]. The value of the standard (p(0) = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by bomb combustion calorimetry, using a rotatory bomb, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K was calculated as -(396.8 ± 0.9) kJ·mol(-1). The enthalpy of sublimation was determined using a transference (transpiration) method in a saturated N(2) stream and a value of the enthalpy of sublimation at T = 298.15 K was derived as (118.3 ± 2.2) kJ·mol(-1). From these results a value of -(278.5 ± 2.4) kJ·mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical calculations at the G3 and G4 levels were performed, and a study of the molecular and electronic structure of the compound has been carried out. Calculated enthalpies of formation are in very good agreement with the experimental value.     

The standard enthalpies of formation of crystalline N-(carboxymethyl)aspartic acid and its aqueous solutions

The energy of combustion of N-(carboxymethyl)aspartic acid (CMAA) was determined by bomb calorimetry in oxygen. The standard enthalpies of combustion and formation of crystalline N-(carboxymethyl)aspartic acid were calculated. The heat effects of solution of crystalline CMAA in water and a solution of sodium hydroxide were measured at 298.15 K by direct calorimetry. The standard enthalpies of formation of CMAA and its dissociation products in aqueous solution were determined.     

Strength of the Zn-N coordination bond in zinc porphyrins on the basis of experimental thermochemistry

The compound, 5,10,15,20-tetrakis(4-methoxyphenyl)porphine zinc(II) (ZnTMPP), was prepared, and its thermochemical properties were experimentally established. The standard molar energy of combustion (Delta(c)U degrees m) was determined from oxygen rotating-bomb combustion calorimetry experiments. The standard molar enthalpies of combustion (Delta(c)H degrees m) and formation (Delta(f)H degrees m) were derived. The enthalpy of sublimation (Delta(cr)(g)H degrees m) was determined by Knudsen effusion at high temperatures. With these results, the standard molar enthalpies of formation and atomization (Delta(at)H degrees m) in the gas state were calculated. A summary of the results at T = 298.15 K (p degrees = 0.1 MPa) is shown in Table 1. Using these results and those previously obtained for the free ligand, 5,10,15,20-tetrakis(4-methoxyphenyl)porphine, the mean dissociation enthalpy for the Zn-N coordination bond is obtained as D(Zn-N) = (160 +/- 9) kJ.mol-1. This value is consistent with the results obtained using the same experimental approach in a similar system (5,10,15,20-tetraphenylporphine, TPP/ZnTPP) reported elsewhere. A discussion of the strength for the Zn-N coordination bond is made in terms of the structural and electronic features of the molecules involved.     

Experimental and theoretical study of thermodynamic properties of levoglucosan

The heat capacity of levoglucosan was measured over the temperature range (5 to 370) K by adiabatic calorimetry. The temperatures and enthalpies of a solid-phase transition and fusion for the compound were found by DSC. The obtained results allowed us to calculate thermodynamic properties of crystalline levoglucosan in the temperature range (0 to 384) K. The enthalpy of sublimation for the low-temperature crystal phase was found from the temperature-dependent saturated vapor pressures determined by the Knudsen effusion method. The thermodynamic properties of gaseous levoglucosan were calculated by methods of statistical thermodynamics using the molecular parameters from quantum chemical calculations. The enthalpy of formation of the crystalline compound was found from the experiments in a combustion calorimeter. The gas-phase enthalpy of formation was also obtained at the G4 level of theory. The thermodynamic analysis of equilibria of levoglucosan formation from cellulose, starch, and glucose was conducted.     

The standard enthalpies of formation of citric and tartaric acids and their dissociation products in aqueous solutions

The energies of combustion of citric and tartaric acids in oxygen were determined by bomb calorimetry. The standard enthalpies of combustion and formation of crystalline citric and tartaric acids were calculated. The heat effects of solution of crystalline acids in water and aqueous potassium hydroxide were determined by direct calorimetry at 298.15 K. The standard enthalpies of formation of acids and their dissociation products in aqueous solution were calculated.     

Experimental and Theoretical Investigation on the Thermochemistry of 3-Methyl-2-benzoxazolinone and 6-Nitro-2-benzoxazolinone

The determination of the reliable thermodynamic properties of 2-benzoxazolinone derivatives is the main goal of this work. Some correlations are established between the energetic properties determined and the structural characteristics of the title compounds, and the reactivity of this class of compounds is also evaluated. Static-bomb combustion calorimetry and high-temperature Calvet microcalorimetry were used to determine, respectively, the standard molar enthalpies of formation in the solid state and the standard molar enthalpies of sublimation, both at T = 298.15 K. Using the results obtained for each compound, the respective gas-phase standard molar enthalpy of formation was derived. High-level quantum chemical calculations were performed to estimate the same property and the results evidence good accordance. Moreover, the gas-phase relative thermodynamic stability of 2-benzoxazolinone derivatives was also evaluated using the respective gas-phase standard molar Gibbs energy of formation. In addition, the relationship between the energetic and structural characteristics of the benzoxazolinones is presented, evidencing the enthalpic increments associated with the presence of a methyl and a nitro groups in the molecule, and this effect is compared with similar ones in other structurally related compounds.     

Two Energetic Ionic Salts of en·PA·H2O and en·TNR: Preparation,Structural Characterization,and Properties

Energetic salts of en · PA · H₂O and en · TNR were synthesized by using ethylenediamine and picric acid (PA) or 2,4,6‐trinitroresorcinol (TNR) as raw materials, and their structures were characterized by elemental analysis and FT‐IR spectroscopy. Single crystals of the title salts were obtained and their structures were determined by single‐crystal X‐ray diffraction. The thermal decomposition behaviors were investigated by DSC and TG‐DTG technologies, furthermore the non‐isothermal kinetic parameters and enthalpies of formation for the salts were calculated. Their combustion heats were measured by oxygen bomb calorimetry and their enthalpies of formation were also calculated based on the combustion heat data. In addition, the detonation pressure (P) and detonation velocities (D) of the salts were predicted by using the K‐J equations. The results indicated that the title salts have potential applications in the field of energetic materials.     

Structure-energy relationship in barbituric acid: a calorimetric, computational, and crystallographic study

This paper reports the value of the standard (p(o) = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K for barbituric acid. The enthalpies of combustion and sublimation were measured by static bomb combustion calorimetry and transference (transpiration) method in a saturated N2 stream and a gas-phase enthalpy of formation value of -(534.3 +/- 1.7) kJ x mol(-1) was determined at T = 298.15 K. G3-calculated enthalpies of formation are in very good agreement with the experimental value. The behavior of the sample as a function of the temperature was studied by differential scanning calorimetry, and a new polymorph of barbituric acid at high temperature was found. In the solid state, two anhydrous forms are known displaying two out of the six hydrogen-bonding patterns observed in the alkyl/alkenyl derivatives retrieved from the Cambridge Crystallographic Database. The stability of these motifs has been analyzed by theoretical calculations. X-ray powder diffraction technique was used to establish to which polymorphic form corresponds to the commercial sample used in this study and to characterize the new form at high temperature.     

Cyclic alkylene carbonates. Experiment and first principle calculations for prediction of thermochemical properties

The standard molar enthalpies of formation of ethylene carbonate, propylene carbonate, and butylene carbonate were measured using combustion calorimetry. Ab initio calculations of molar enthalpies of formation of alkylene carbonates were performed using the G3MP2 method. The calculated values are in excellent agreement with available experimental data. Ring strain corrections were quantified for the refinement of the group-contribution method for prediction of enthalpies of formation and vaporization of alkylene carbonates.     

Thermochemical properties of 1-butyl-3-methylimidazolium nitrate

Heat capacity for 1-butyl-3-methylimidazolium nitrate [C₄mim][NO₃] in the temperature range (5–370) K has been measured by adiabatic calorimetry. Temperatures and enthalpies of its phase transitions have been determined. Thermodynamic functions have been calculated for the crystalline and the liquid states. Phase transition temperatures for set of nitrate salts have been compared. Enthalpy of combustion and enthalpy of formation for crystalline [C₄mim][NO₃] have been determined using a static-bomb isoperibol combustion calorimeter. A correlation scheme for the estimation of C_p of ionic liquids has been developed.     

A calorimetric and computational study of the thermochemistry of halogenated 1-phenylpyrrole derivatives

The standard molar enthalpies of formation, in the crystalline phase, of three halogenated 1-phenylpyrrole derivatives, namely 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were derived from the respective enthalpies of combustion, measured by rotating-bomb combustion calorimetry. Their enthalpies of sublimation, at T = 298.15 K, were obtained from the Knudsen mass-loss effusion technique. From these two experimental parameters, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were calculated, respectively, as (26.2 ± 2.4) kJ · mol⁻¹, (196.2 ± 2.5) kJ · mol⁻¹, and (311.5 ± 2.4) kJ · mol⁻¹.The gas-phase enthalpies of formation of both fluorine and chlorine compounds were estimated by G3(MP2)//B3LYP computations. For the iodine compound, the B3LYP/6-311G(d):ECP46MDF approach was employed. Additionally, the DFT calculations were extended to estimate the enthalpy of formation of the bromine derivative, 1-(4-bromophenyl)pyrrole, performed at the B3LYP/6-311G(d) level of theory.     

Experimental and computational study of the thermochemistry of the fluoromethylaniline isomers

The standard (po = 0.1 MPa) molar enthalpies of formation in the condensed phase of seven isomers of fluoromethylaniline were derived from the standard molar energies of combustion, in oxygen, to yield CO2(g), N2(g) and HF.10H2O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vaporization or sublimation of these compounds, also at T = 298.15 K, were determined using Calvet microcalorimetry, while the enthalpies of fusion of the solid compounds were determined by differential scanning calorimetry. The standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived from the former two experimental quantities. G3MP2//B3LYP calculations were performed for all possible fluoromethylanilines allowing the estimation of data for the isomers that were not studied experimentally. The Cox scheme was applied with two different approaches for the estimation of the standard molar enthalpies of formation of all the isomers studied, and this led to the conclusion that the literature values for the enthalpies of formation of the meta and para isomers of methylaniline seem to be not reliable. Further G3MP2//B3LYPs calculations on the methylaniline isomers yielded new values for the standard molar enthalpies of formation of the isomers of methylaniline, which have been tested under the Cox scheme, resulting in better estimates.