Thermodynamics of semi-interpenetrating polymeric networks based on crosslinked poly(cyanurate) and linear poly(urethane) in the temperature region from T → 0 to 350 K

The temperature dependences of the heat capacity of linear poly(urethane) (PU) (M _n = 4·10⁴), which was synthesized from 4,4′-diphenylmethane diisocyanate, oligo(butylene glycol adipinate) (M _n = 1000), and chain-elongating agent butane-1,4-diol, and three samples of related semi-interpenetrating polymeric networks containing 25, 50, and 75 wt.% of crosslinked poly(bisphenol A) cyanurate were studied in a region of 6–350 K by adiabatic vacuum calorimetry. Their combustion energies were determined in a calorimeter with a static bomb and an isothermic shell. The thermodynamic functions of the compounds under study for the temperature region from T → 0 to 350 K, enthalpies of combustion, and thermodynamic characteristics of formation from simple substances at T = 298.15 K and p = 0.1 mPa were calculated. The thermodynamic parameters of formation of the semi-interpenetrating networks were calculated. The dependences of the isotherms of the thermodynamic properties and thermodynamic compatibility of the semi-interpenetrating networks on their composition were determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 648–654, April, 2006.     

Zur Calorimetrie der Bismutoxidhalogenide. II. Bismutoxidbromide

Calorimetry of Bismuth Oxidhalides. II. Bismuth Oxidebromides The heat solution of all known solid phases in the system Bi₂O₃/BiBr₃ in 4n HBr were investigated. To compare the data they were converted to the standardized formula Bi₂O_3?y/2Br_yBr_y with 0 ? y ? 2. The enthalphies of formation of the complex bismuthoxidebromides are based on the enthalpies of Bi₂O_3,f HBr_,Lsg and H₂O circumventing the value for Bi(OH)_3,Lsg.     

The energies of dissociation of the N—O bonds in pyridine 1-oxide derivatives

The enthalpies of combustion of some pyridine derivatives in the solid state have been measured by precision bomb calorimetry, and their enthalpies of formation have been calculated. The enthalpies of sublimation of these compounds have been determined from the experimental temperature dependences of saturated vapor pressure using the Clausius-Clapeyron equation. The enthalpies of combustion, formation, and sublimation are the following (kJ mol^–1): -3360.9±2.1, -0.5±2.1, and 79.1±1.3, respectively, for 4-methylpyridine 1-oxide; -2551.0±1.7, 11.7±1.7, and 89.1±2.5, respectively, for 4-nitropyridine 1-oxide;-2355.6±1.3, 102.1±1.3, and 106.3±2.9 for 2,4,6-trinitropyridine 1-oxide; and -2287.6±1.3, 34.3±1.3, and 101.7±2.9 for 2,4,6-trinitropyridine. The enthalpies of formation in the solid state and the enthalpies of sublimation of pyridine derivatives obtained together with the literature data allowed the energies of dissociation of the donor-acceptor N—O bonds in pyridine 1-oxides to be calculated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 660–662, April, 1995.     

Thermochemical properties of polycyclic hydrocarbons including fragments of norbornane and small cycles

Combustion enthalpies of three polycyclic hydrocarbons were measured by the precision bomb calorimetry method and their enthalpies of formation in the liquid state were calculated: for pentacyclo[6.3.1.1^3.6.0^2.7.0^9.11]tridecene, –7713.9±3.8 and 25.8±3.8 kJ mol^–1; for 10-met hylpentacyclo[6.3.1.1^3.6.O^2,.7.0^9.11 It ridecene, -8348.8±3.9 and -18.7+-3.9 k] mol^–1; and for 11-methylpentacyclo[6.4.1.1^3.6.0^2.7.0^9.12]tetradecene-10-spirocyclopropane,clopropane, –10157.9±3.4 and 38.1±3.8 kJ mol^–1. The thermochemical I parameters obtained agree with calculated values as well as with experimental and calculated enthalpies of formation of some hydrocarbons that contain the same fragments as the compounds studied.The authors thank Academician O. M. Nefedov and Yu. V. Tomilov for submitting the samples and for discussion of the results obtained.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2676–2678, November, 1996.     

Thermodynamics of Silicon Nitride. Standard molar enthalpy of formation of amorphous Si3N4 at 298.15 K

The standard molar enthalpy of formation Δ_f H _m ⁰=–760±12 kJ for amorphous silicon nitride a-Si₃N₄ has been determined from fluorine combustion calorimetry measurements of the massic energy of the reaction: a-Si₃N₄(s)+6F₂(g)=3SiF₄(g)+2N₂(g). This value combined with Δ_f H _m ⁰= –828.9±3.4 kJ for a-Si₃N₄ indicates that determined for the first time molar enthalpy change for the transition from amorphous to α-crystalline form Δ_trs H _m ⁰=69±13 kJ is very evident, in spite of its large uncertainty range resulting from impurity corrections. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enthalpies of formation of methoxybenzoic acids and their dependence on structure

The energy of combustion of 2,5-dimethoxybenzoic acid has been determined using a static bomb calorimeter. The vapor pressures of the compound have been measured over a 18 K temperature interval by the Knudsen effusion technique. Heat capacity measurements betweenT=270 K andT=338 K were carried out by DSC. From these experimental results the standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous state at the temperature 298.15 K have been derived. With this compound, the series of mono- and dimethoxy-benzoic acids have been completed. Their_f H _m ^o values were expressed by an additive relationship, taking into account the number of methoxy groups and the number of all 1,2 interactions: an accuracy of 3.3 kJ·mol^–1 was achieved. In an alternative approach the substituent effect of the methoxy groups was evaluated within the framework of isodesmic reactions. The effect of disubstitution was referred to mono derivatives and the excess energy—the so-called buttressing effect—was evaluated (2–24 kJ· mol^–1 for individual bis derivatives). These values were explained in terms of the conformation of the methoxy group around the C_ar-O bond.     

Enthalpies of Formation of the Tellurites of the Rare Earths Gd, Tb, Dy, Tm and Yb

By using a DSK of the French firm Seteram, the standard enthalpies of formation of 5 tellurites and 5 tetratellurites of the rare earths Gd, Tb, Dy, Tm and Yb were determined for the first time. Three parallel determinations for each sample were compared. The results are very similar, which is an indication of the great reliability of the method used and the correctness of the data obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamics of carbyne

Published data on the thermodynamic properties of carbyne are analyzed and generalized. The thermodynamic properties of carbyne are compared with the properties of other allotropic modifications of carbon (fullerenes, diamonds, and graphite). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 971–980, June, 2000.     

Determination of Standard Enthalpies of Formation of the Tellurites of the Rare Earths Y,La, Ce and Pr by DSC Method

The standard enthalpies of tellurites of Y, La, Ce and Pr were determined by differential scanning calorimetric (DSC) method. The completeness of the chemical reactions between the metal oxides and tellurous oxide were checked by DSC and X-ray powder diffraction methods. The calculated standard enthalpies are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

嘧霉胺的标准生成焓及其抗灰葡萄孢菌作用

用苯胺、氨基氰、乙酰丙酮三种物质合成了杀菌剂嘧霉胺(C12N3H13).并用溶解量热法在常压、298.15K下,分别测定了苯胺、氨基氰、乙酰丙酮和嘧霉胺在混合溶剂(VDMF:VDMSO=2:1)中的溶解焓:ΔsHmΘ(C6NH7(l),298.15K)=-(12.48±0.16)kJmol-1、ΔsHmΘ(NH2CN(s),298.15K)=-(8.06±0.42)kJmol-1、ΔsHmΘ(CH3COCH2COCH3(l),298.15K)=(1.26±0.03)kJmol-1和ΔsHmΘ[C12N3H13(s),298.15K]=(13.84±0.12)kJmol-1.根据热化学原理求出了298.15K时,合成反应的标准反应热ΔrHmΘ=-(35.65±0.47)kJmol-1,以及嘧霉胺(C12N3H13(s))的标准摩尔生成焓ΔfHmΘ(C12N3H13(s),298.15K)=(198.5±1.5)kJmol-1;用TAMair微量热仪测定了嘧霉胺(C12N3H13(s))在301.15K时对灰葡萄孢菌作用的产热曲线,根据产热曲线求算了在嘧霉胺作用下,灰葡萄孢菌生长代谢的最大发热功率Pmax、最大产热功率的时间tmax、速率常数k和抑制率I等热动力学参数.结果表明:嘧霉胺在低浓度下对灰葡萄孢菌有刺激作用,高浓度下为抑制作用,即嘧霉胺对微生物的生长具有双向生物效应,也称为Hormsis效应.     

Complex formation of rare-earth elements with 1,10-phenanthroline

Complex formation in a Ln(III)-1,10-phenanthroline-ethyl acetate system, where Ln = La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, or Lu, is studied by spectrophotometric methods. The stability of the complexes is estimated. The changes in the thermodynamic parameters of complex formation and the bonding character in the lanthanide complexes with 1,10-phenanthroline and 2,2′-dipyridyl are ascertained and compared.     

Gas-phase enthalpies of formation of the fluorobenzenes family and their dewar isomers from ab initio calculations

The standard gas-phase enthalpies of formation, at T = 298.15 K, of the complete series of fluorobenzene and their corresponding dewar isomers have been determined by means of the CBS-QB3 and G3MP2B3 composite approaches. These values have been estimated by using appropriate supporting reactions, such as, reactions of atomization or of atom substitution. The results show that there is a linear dependence between the enthalpy of the most stable n-fluorobenzene and the corresponding n-fluorodewar benzene (n = 0, 1, …, 6). Further, the estimates are always more negative than the experimental results and so, suggested enthalpies of formation for 1,2,3-, 1,2,4- and 1,3,5-trifluorobenzenes and for 1,2,3,4- and 1,2,3,5-tetrafluorobenzenes are those retrieved from G3MP2B3 calculations added by 8 kJ/mol. The interaction of four different M⁺ ions with fluorobenzene and the three difluorobenzenes shows that the σ-interaction with 1,2-difluorobenzene is stronger than π-interaction on these fluorobenzenes.     

Enthalpies of formation of Ni-Sn compounds

Enthalpies of formation (Δ_fH) of nickel-tin compounds have been measured by direct reaction calorimetry: (approximate value); .Standard states are solid Ni and liquid Sn at the respective working temperatures: 728, 1288, 1389, 1332, 943 and 846 K.The enthalpy of formation of the Ni₃Sn high-temperature form is measured for the first time, while that of Ni₃Sn₂_LT must be considered as approximate because the corresponding calorimetric reaction was incomplete.The chemical and phase compositions of the specimens have been verified by electron probe microanalyses and by high- and room-temperature X-ray diffraction analyses. Unidentified thermal effects have been observed in the Ni₃Sn₂ phases region.     

Accurate prediction of the enthalpies of formation for xanthophylls

This study investigates the applications of computational approaches in the prediction of enthalpies of formation (ΔH(f)) for C-, H-, and O-containing compounds. Molecular mechanics (MM4) molecular mechanics method, density functional theory (DFT) combined with the atomic equivalent (AE) and group equivalent (GE) schemes, and DFT-based correlation corrected atomization (CCAZ) were used. We emphasized on the application to xanthophylls, C-, H-, and O-containing carotenoids which consist of ～ 100 atoms and extended π-delocaization systems. Within the training set, MM4 predictions are more accurate than those obtained using AE and GE; however a systematic underestimation was observed in the extended systems. ΔH(f) for the training set molecules predicted by CCAZ combined with DFT are in very good agreement with the G3 results. The average absolute deviations (AADs) of CCAZ combined with B3LYP and MPWB1K are 0.38 and 0.53 kcal/mol compared with the G3 data, and are 0.74 and 0.69 kcal/mol compared with the available experimental data, respectively. Consistency of the CCAZ approach for the selected xanthophylls is revealed by the AAD of 2.68 kcal/mol between B3LYP-CCAZ and MPWB1K-CCAZ.     

Standard enthalpy of formation of lanthanum oxybritholites

Lanthanum-bearing silicate-oxyapatites or britholites, Ca_10–xLax(PO₄)_6–x(SiO₄)_xO with 1≤x≤6, have been synthesized by solid state reaction at high temperature. They were characterized by X-ray diffraction and IR spectroscopy. Using two microcalorimeters, the heat of solution of these compounds have been measured at 298 K in a solution of nitric and hydrofluoric acid. A strained least squares method was applied to the experimental results to obtain the solution enthalpies at infinite dilution, and the mixing enthalpy in two steps. In the first step the mixing enthalpy obtained is referenced to the britholite monosubstituted and to the oxysilicate. The mixing enthalpy referenced to the oxyapatite and to the oxysilicate is then extrapolated. In order to determine the enthalpies of formation of all the terms of the solution, thermochemical cycles were proposed and complementary experiments were performed. The results obtained show a decrease of the enthalpy of formation with the amount of Si and La introduced in the lattice. This was explained by the difference in the bond energies of (Ca–O, P–O) and (La–O, Si–O).     

Low-temperature heat capacities and standard molar enthalpy of formation of aspirin

Molar heat capacities (C _p,m) of aspirin were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 383 K. No phase transition was observed in this temperature region. The polynomial function of C _p,m vs. T was established in the light of the low-temperature heat capacity measurements and least square fitting method. The corresponding function is as follows: for 78 K≤T≤383 K, C _p,m/J mol^-1 K^-1=19.086X ⁴+15.951X ³-5.2548X ²+90.192X+176.65, [X=(T-230.50/152.5)]. The thermodynamic functions on the base of the reference temperature of 298.15 K, {ΔH _T -ΔH _298.15} and {S _T-S _298.15}, were derived. Combustion energy of aspirin (Δ_c U _m) was determined by static bomb combustion calorimeter. Enthalpy of combustion (Δ_c H ^o _m) and enthalpy of formation (Δ_f H ^o _m) were derived through Δ_c U _m as - (3945.26±2.63) kJ mol^-1 and - (736.41±1.30) kJ mol^-1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Standard enthalpy of formation of platinum hydrous oxide

Standard enthalpies of formation of amorphous platinum hydrous oxide PtH_2.76O_3.89 (Adams' catalyst) and dehydrated oxide PtO_2.52 at T=298.15 K were determined to be -519.6±1.0 and -101.3 ±5.2 kJ mol^-1, respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO₂ was estimated to be -80 kJ mol^-1 based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation energy is 246 kJ mol^-1 at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide an energetic reason why platinum hydrous oxide is non-stoichiometric. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamics of C70 fullerence in the 0–390 K temperature range

The temperature dependence of heat capacity of C₇₀ fullerene was studied by calorimetry in the range between 6 and 390 K. Phase transitions were established and their thermodynamic characteristics were determined. From the experimental data obtained, the thermodynamic functionsH ^o (T)-H ^o(0),S ^o(T),G ^o(T)-H ^o(0) for temperatures between 0 and 390 K were calculated. The results were used to calculate the standard values of Δ_f S ^o, Δ_f G ^o, and logK _f ^o for the formation of C₇₀ from graphite. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 647–650, April, 1998.     

The standard enthalpy of formation of silver pivalate

The standard enthalpy of combustion of crystalline silver pivalate, (CH₃)₃CC(O)OAg (AgPiv), was determined in an isoperibolic calorimeter with a self-sealing steel bomb, Δ_c H ⁰ (AgPiv, cr)= −2786.9±5.6 kJ mol⁻¹. The value of standard enthalpy of formation was derived for crystalline state: Δ_f H ⁰(AgPiv,cr)= −466.9±5.6 kJ mol⁻¹. Using the enthalpy of sublimation, measured earlier, the enthalpy of formation of gaseous dimer was obtained: Δ_f H ⁰(Ag₂Piv₂,g)= −787±14 kJ mol⁻¹. The enthalpy of reaction (CH₃)₃CC(O)OAg(cr)=Ag(cr)+(CH₃)₃CC(O)O^.(g) was estimated, Δ_r H ⁰=202 kJ mol⁻¹.