Features of the Diels-Alder reaction between 9,10-diphenylanthracene and 4-phenyl-1,2,4-triazoline-3,5-dione

The Diels-Alder reaction between substituted anthracenes 1a?1j and 4-phenyl-1,2,4-triazoline-3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10-atoms of substituted anthracenes. The orthogonality of the two phenyl groups at the 9,10-position of diene 1a is found to shield 9,10-reactive centers. No dienophiles with C=C bonds are shown to participate in the Diels-Alder reaction with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4-phenyl-1,2,4-triazoline-3,5-dione. It is shown that attachment occurs on the less active but sterically accessible 1,4-reactive center of diene 1a. The structure of adduct 3a is proved by ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. The following parameters are obtained for reaction 1a + 2 ? 3a in toluene at 25°C: K _eq = 2120 M^?1, ΔH _f ^≠ = 58.6 kJ/mol, ΔS _f ^≠ = ?97 J/(mol K), ΔV _f ^≠ = ?17.2 cm³/mol, ΔH _b ^≠ = 108.8 kJ/mol, ΔS _b ^≠ = 7.3 J/(mol K), ΔV _b ^≠ = ?0.8 cm³/mol, ΔH _r-n = ?50.2 kJ/mol, ΔS _r-n = ?104.3 J/(mol K), ΔV _r-n = ?15.6 cm³/mol. It is concluded that the values of equilibrium constants of the reactions 1a?1j + 2 ? 3a?3j vary within 4 × 10¹?10¹¹ M^?1.     

Enthalpy of formation of wulfenite (natural lead molybdate)

A thermochemical study of wulfenite, i.e., natural lead molybdate PbMoO₄ (Kyzyl-Espe field deposit, Central Kazakhstan), is performed on a Setaram high-temperature heat-flux Tian-Calvet microcalorimeter (France). Enthalpies of the formation of wulfenite from oxides Δ_f H _ox ^o (298.15 K) = ?88.5 ± 4.3 kJ/mol and simple substances Δ_f H°(298.15 K) = ?1051.2 ± 4.3 kJ/mol were determined by means of melt calorimetry. The Δ_f G°(298.15 K) of wulfenite corresponding to ?949.1 ± 4.3 kJ/mol was calculated using data obtained earlier for S°(298.15 K) = 161.5 ± 0.27 J/(K mol).     

Crystal structure and vapor pressure of a copper(II) complex with 2,2,6,6-tetramethyl-4-fluoroheptane-3,5-dione

Synthesis and single crystal X-ray diffraction study were carried out for copper(II) 2,2,6,6-tetramethyl-4-fluoroheptane-3,5-dionate (Bruker AXS P4 automated diffractometer, MoK _α radiation). Crystal data for C₂₂H₃₆CuF₂O₄: a = 5.9165(4) Å, b = 10.2787(7) Å, c = 10.5223(8) Å, α = 81.383(3)°, β = 76.106(3)°, γ = 83.778(3)°, space group P $\bar 1$ , V = 612.42(7) ų, Z = 1, d _x = 1.264 g/cm³. The structure is molecular; the copper atom has a square plane coordination formed by the oxygen atoms of two β-diketonate ligands; the average Cu-O distance is 1.895 Å, ∠O-Cu-O 92.5°. Only van der Waals interactions are realized between the molecules in the structure. The temperature dependences of the saturated vapor pressure were studied by the mass transfer technique, and the standard thermodynamic parameters of sublimation were derived for the complex, ΔH _subl ⁰ = 115.6 ± 1.1 kJ/mol, ΔS _subl ⁰ = 204.9 ± 2.5 J/mol·K.     

Transport properties of ZrV2O7-V2O5 composites with liquid-channel grain boundary structure

Transport properties (conductivity, transport numbers of oxygen ions, oxygen permeability) are studied for new composites of ZrV₂O₇-25, 30, 35, 40 mol % of V₂O₅ with a liquid-channel grain boundary structure (LGBS) at 680–740°C. It is shown that the composite of ZrV₂O₇-40 mol % of V₂O₅ with LGBS has high selective oxygen permeability of 1.1 × 10^?8 mol cm^?2 s^?1 (T = 740°C, $P'_{O_2 } $ = 0.21 atm, $P''_{O_2 } $ = 0.003 atm, L = 2 mm) and can be used as an ion-transport membrane for separation of oxygen from air.     

Copolymerization of styrene with acrylonitrile and maleic anhydride

The complex formation constants for styrene (donor)-acrylonitrile (acceptor) and styrene-maleic anhydride (acceptor) systems are found to be 0.19 ± 0.01 and 0.28 ± 0.01 l/mol (¹H NMR, CCl₄, 298 K); the same values are characteristic for three-component systems of these monomers. The calculated ΔH ₀ values (the AM1 method) for styrene-acrylonitrile (C₁) and styrene-maleic anhydride (C₂) complexes comprise ?1.24 and ?2.30 kJ/mol. Changes in charges on double bonds of complex-bonded molecules are in the range from 0.001 to 0.006 au. These values are typical of π-π complexes. By analyzing the composition and rate of bulk copolymerization (333 K, 0.03 mol/l AIBN), we have shown that two complexes are involved in chain propagation: r ₁ = $ k_{2C_1 } /k_{2C_2 } $ = 0.26 ± 0.015 and r ₂ = $ k_{3C_2 } /k_{3C_1 } $ = 4.17 ± 0.143.     

The Formation and Stability of the [FePy3Cl3]· Py Clathrate in the Pyridine–Iron(III) Chloride System: Phase Diagram and Solid–Gas Equilibria Study

The phase diagram of the pyridine–iron(III) chloride system has been studied for the 223–423 K temperature and 0–56 mass-% concentration ranges using differential thermal analysis (DTA) and solubility techniques. A solid with the highest pyridine content formed in the system was found to be an already known clathrate compound, [FePy₃Cl₃]·Py. The clathrate melts incongruently at 346.9 ± 0.3 K with the destruction of the host complex: [FePy₃Cl₃]·Py_(solid)=[FePy₂Cl₃]_(solid) + liquor. The thermal dissociation of the clathrate with the release of pyridine into the gaseous phase (TGA) occurs in a similar way: [FePy₃Cl₃]·Py_(solid)=[FePy2Cl₃]_(solid) + 2 Py_(gas). Thermodynamic parameters of the clathrate dissociation have been determined from the dependence of the pyridine vapour pressure over the clathrate samples versus temperature (tensimetric method). The dependence experiences a change at 327 K indicating a polymorphous transformation occurring at this temperature. For the process ${1 \over 2}[\hbox{FePy}_{3}\hbox{Cl}_{3}]\cdot \hbox{Py}_{\rm (solid)} = {1 \over 2}[\hbox{FePy}_{2}\hbox{Cl}_{3}]_{\rm (solid)} + \hbox{Py}_{\rm (gas)}$ in the range 292–327 K, ΔH $^{0}_{298}$ =70.8 ± 0.8 kJ/mol, ΔS $^{0}_{298}$ =197 ± 3 J/(mol K), ΔG $^{0}_{298}$ =12.2 ± 0.1 kJ/mol; in the range 327–368 K, ΔH $^{0}_{298}$ =44.4 ± 1.3 kJ/mol, ΔS $^{0}_{298}$ =116 ± 4 J/(mol K), ΔG $^{0}_{298}$ =9.9 ± 0.3 kJ/mol.     

Thermochemical study of [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O

The product from reaction of samarium chloride hexahydrate with salicylic acid and Thioproline, [Sm(C₇H₅O₃)₂·(C₄H₆NO₂S)]·2H₂O, was synthesized and characterized by IR, elemental analysis, molar conductance, and thermogravimetric analysis. The standard molar enthalpies of solution of [SmCl₃·6H₂O(s)], [2C₇H₆O₃(s)], [C₄H₇NO₂S(s)] and [Sm(C₇H₅O₃)₂·(C₄H₇NO₂S)·H₂O(s)] in a mixed solvent of absolute ethyl alcohol, dimethyl sulfoxide(DMSO) and 3 mol L^?1 HCl were determined by calorimetry to be Δ_s H _m ^Φ [SmCl₃ δ6H₂O (s), 298.15 K]= ?46.68±0.15 kJ mol^?1 Δ_s H _m ^Φ [2C₇H₆O₃ (s), 298.15 K]= 25.19±0.02 kJ mol^?1, Δ_s H _m ^Φ [C₄H₇NO₂S (s), 298.15 K]=16.20±0.17 kJ mol^?1 and Δ_s H _m ^Φ [Sm(C₇H₅O₃)₂·(C₄H₆NO₂S)]·2H₂O (s), 298.15 K]= ?81.24±0.67 kJ mol^?1. The enthalpy change of the reaction (1) $$ SmCl_3 \cdot 6H_2 O(s) + 2C_7 H_6 O_3 (s) + C_4 H_7 NO_2 S(s) = Sm(C_7 H_5 O_3 )_2 \cdot (C_4 H_6 NO_2 S) \cdot 2H_2 O(s) + 3HCl(g) + 4H_2 O(1) $$ was determined to be Δ_s H _m ^Φ =123.45±0.71 kJ mol^?1. From date in the literature, through Hess’ law, the standard molar enthalpy of formation of Sm(C₇H₅O₃)₂(C₄H₆NO₂S)δ2H₂O(s) was estimated to be Δ_s H _m ^Φ [Sm(C₇H₅O₃)₂·(C₄H₆NO₂S)]·2H₂O(s), 298.15 K]= ?2912.03±3.10 kJ mol^?1.     

Solvent and external pressure effects on the ratio of the cyanoisopropyl radical recombination and disproportionation rates

A GC-MS analysis of the azobisisobutyronitrile thermal decomposition products of in solutions at 80°C showed that the ratio of recombination and disproportionation rates of the cyanoisopropyl radical does not depend on the medium viscosity, but increases when the internal pressure of the solvent increases according to the log(k _dispr/k _rec) = ?1.25 + 0.096 P _int ^0.5 law. This means that the activation volume corresponding to recombination is larger than that corresponding to disproportionation. It follows from the relationship log(k _dispr/k _rec) = (ΔV _rec ^≠ ? Δv _dispr ^≠ )ΔP/RT that, for the decomposition of the substrate in benzene under a pressure of 0.5–4.0 kbar, the difference between the activation volumes is ΔV _rec ^≠ ? ΔV _dispr ^≠ = 8 cm³/mol.     

Kinetics and mechanism of the oxidation of acrylic acid and methyl methacrylate

The kinetics of the initiated oxidation of acrylic acid and methyl methacrylate in the liquid phase were studied volumetrically by measuring oxygen uptake during the reaction. Both processes proceed via the chain mechanism with quadratic-law chain termination. The oxidation rate is described by the equation w = k ₂/(2k ₆)^1/2[monomer]w _i ^1/2 , where w _i is the initiation rate and k ₂ and k ₆ are the rate constants of chain propagation and termination. The parameter k ₂/(2k ₆)^1/2 is 7.58 × 10^?4 (l mol^?1 s^?1)^1/2 for acrylic acid oxidation and 2.09 × 10^?3 (l mol^?1 s^?1)^1/2 for the oxidation of methyl methacrylate (T = 333 K). For the oxidation of acrylic acid, k ₂ = 2.84 l mol^?1 s^?1 (T = 333 K) and the activation energy is E ₂ = 54.5 kJ/mol; for methyl methacrylate oxidation, k ₂ = 2.96 l mol^?1 s^?1 (T = 333 K) and E ₂ = 54.4 kJ/mol. The enthalpies of the reactions of RO ₂ ^? with acrylic acid and methyl methacrylate were calculated, and their activation energies were determined by the intersecting parabolas method. The contribution from the polar interaction to the activation energy was determined by comparing experimental and calculated E ₂ values: ΔE _μ = 5.7 kJ/mol for the reaction of RO ₂ ^? with acrylic acid and ΔE _μ = 0.9 kJ/mol for the reaction of RO ₂ ^? with methyl methacrylate. Experiments on the spontaneous oxidation of acrylic acid provided an estimate of the rate of chain initiation via the reaction of oxygen with the monomer: w _i,0 = (3.51 ± 0.85) × 10^?11 mol l^?1 s^?1 (T = 333 K).     

Thermodynamic properties and oxygen stoichiometry of Ba2Cu3O5 + δ

The thermodynamic properties and oxygen stoichiometry of Ba₂Cu₃O_{5 + δ} are studied by means of the electromotive force (EMF) with a fluoride electrolyte, dissolution calorimetry, and thermogravimetry. It is shown that the temperature dependence of the Gibbs energy of the formation of barium cuprate from simple oxides and oxygen in the temperature range of 860–1120 K can be described by the polynomial Δ_{f, ox} G ^°(Ba₂Cu₃O_{5 + δ}) ± 0.1 (kJ/mol) = ?291.78 + 1.127T ? 0.13207 TlnT (kJ/mol).     

Bildungsenthalpie von Uranpentachlorid

The standard enthalpy of formation of UCl₅ has been determined as ΔH _f ^,298/0 UCl₅ (s)=?247.7±0.5 kcal/mol (?1036.4±2.1 kJ/mol) by reacting uranium with chlorine gas in the presence of excess liquid chlorine at 298° K.     

Thermochemistry of hydroxymethylphenol isomers

The standard (p° = 0.1 MPa) molar enthalpies of formation in the crystalline state of the 2-, 3- and 4-hydroxymethylphenols, $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr)}} = \, - ( 3 7 7. 7 \pm 1. 4)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr) }} = - (383.0 \pm 1.4) \, \,{\text{kJ}}\,{\text{mol}}^{ - 1} $ and $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr)}} = - (382.7 \pm 1.4)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , respectively, were derived from the standard molar energies of combustion, in oxygen, to yield CO₂(g) and H₂O(l), at T = 298.15 K, measured by static bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of hydroxymethylphenol with the temperature, from which the standard molar enthalpies of sublimation were derived using the Clausius–Clapeyron equation. The results were as follows: $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (99.5 \pm 1.5)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (116.0 \pm 3.7) \,{\text{kJ}}\,{\text{mol}}^{ - 1} $ and $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (129.3 \pm 4.7)\,{\text{ kJ mol}}^{ - 1} $ , for 2-, 3- and 4-hydroxymethylphenol, respectively. From these values, the standard molar enthalpies of formation of the title compounds in their gaseous phases, at T = 298.15 K, were derived and interpreted in terms of molecular structure. Moreover, using estimated values for the heat capacity differences between the gas and the crystal phases, the standard (p° = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, were derived for the three hydroxymethylphenols.     

Ionization of aqueous benzoic acid: Conductance and thermodynamics

Molar conductances of dilute aqueous benzoic acid solutions are presented for temperatures from 5 to 80°C. The data have been analyzed to give acid dissociation constants as well as ΔH ^o, ΔS ^o, and ΔC _p ^o for the ionization process and the limiting conductance of the benzoate ion. The conductance-viscosity product changes less than 4% over the temperature range, indicating that the interaction of the benzoate ion with the solvent changes little if at all with increasing temperature. The pK _a(m) vs.T data show that ΔH ^o decreases quadratically while ΔC _p ^o increases linearly withT although, over the 75°C range, ΔC _p ^o increases only about 6 cal-mole^?1 deg^?1 around an average of ?37 cal-mole^?1deg^?1. The acid dissociation constants as derived from the conductance-molal concentration analysis show an average uncertainty of about 0.1% and are fitted to within about 0.01% by the equation $$p{\text{K}}_{\text{a}} (m) = - 75.5422 + 3136.34/T + 28.7965 log T - 6.8139 {\text{x}} 10^{ - 3{\text{T}}} $$ whereT is the absolute temperature.     

Thermodynamic transfer functions for urea and thiourea from water to water-tetrahydrofuran mixtures from precise vapor-pressure measurements

The rate of change of the standard chemical potential with solvent composition, \(\partial \bar G_0 /\partial Z\) , has been calculated from precise vapor-pressure measurements for urea at three temperatures and for thiourea at 298.15°K in water-tetrahydrofuran (THF) mixtures. From these results the standard free energy of transfer ΔG _t ^o of the solutes from water to various water-THF mixtures has been obtained together with the standard molar entropy ΔS _t ^o and the standard molar enthalpy ΔH _t ^o of transfer at 298.15°K in the case of urea. The quantity ΔG _t ^o for urea is negative in the water-rich region and positive for mole fractions THF>0.2. There is a nearly complete compensation between ΔH _t ^o andTΔS _t ^o at 298.15°K up to mole fraction THF=0.5. These phenomena can be partly related to the structure in H₂O-THF mixtures.     

Synthesis and crystal structure of Cs2[(UO2)2(C2O4)3] and Cs2[UO2(C3H2O4)2] · H2O

Cs₂[(UO₂)₂(C₂O₄)₃] (I) and Cs₂[UO₂(C₃H₂O₄)₂] · H₂O (II) have been synthesized and studied by X-ray diffraction. The crystals of complexes I and II are monoclinic: a = 8.1453(2) Å, b = 8.9831(2) Å, c = 11.3897(4) Å, β = 104.0950(10)°, V = 808.29(4) ų, space group P2₁/n, Z = 2, and R ₁ = 0.0255 for I and a = 9.6998(2) Å, b = 17.8686(3) Å, c = 8.2074(2) Å, β = 97.5780(10)°, V = 1410.10(5) ų, space group P2₁/c, Z = 4, and R ₁ = 0.0287 for II. The uranium-containing structural units of complexes I and II are [(UO₂)₂(C₂O₄)₃]^2? chains and [UO₂(C₃H₂O₄)₂] ₂ ^4? dimers, which belong to the AK _0.5 ⁰² T¹¹ and AT¹¹B⁰¹ crystallochemical groups (A = UO ₂ ²⁺ , K⁰² and T¹¹ = C₂O ₄ ^2? , T¹¹ and B⁰¹ = C₃H₂O ₄ ^2? ) of uranyl complexes.     

Thermodynamic parameters of phase transitions of perfluoro-N-(4-methylcyclohexyl)piperidine

The heat capacity of perfluoro-N-(4-methylcyclohexyl)piperidine (PMCP) was measured by low-temperature adiabatic calorimetry. The purity of the substance (N ₁ = 99.66 mol %), triple point temperature (T _tp = 293.26 K), and enthalpy of fusion (Δ_fus H _m ^° = 8.32 kJ/mol) were determined. The enthalpy of vaporization was measured by calorimetry at 298.15 K (Δ_vap H _m ^° (298.15 K) = 56.56 kJ/mol). The temperature dependence of the saturated vapor pressure of PMCP over the pressure range 6.2–101.6 kPa was determined by comparative ebulliometry. The normal boiling point (T _n.b. = 460.74 K), ehthalpies of vaporization (at various temperatures), and critical parameters of PMCP were calculated. The calculated and experimental values of Δ_vap H _m ^° (298.15 K) agree to within measurement errors, which proves the reliability of these values and pT parameters used in calculations.     

Equilibria of aqueous solutions of isopolyniobotungstates-6 with c Nb : c W = 1 : 5

Complex formation in the Nb₆O ₁₉ ^8? -WO ₄ ^2? -H⁺-H₂O system with c _Nb : c _W = 1 : 5 and varied c _{Nb + W} ⁰ = 10^?2, 5 × 10^?3, 2.5 × 10^?3, and 10^?3 mol/L) has been studied. Distribution diagrams were simulated for individual niobium(V) and tungsten(VI) isopolyanions and mixed isopolyniobotungstates for $Z = \frac{{c_{H^ + }^0 }}{{c_{Nb + W}^0 }} = 0 - 3.0$ in an NaCl background electrolyte. We have shown that isopolyniobotungstates-6 of composition H _x NbW₅O ₁₉ ^{(3 ? x)?} are formed via H _x Nb _n W_6?n O ₁₉ ^{(2 + n ? x)?} (n=2, 3, 5) ions. The concentration formation constants and thermodynamic formation constants of isopolyniobotungstate anions (IPNTAs) in aqueous solution have been calculated. Salt Tl₃NbW₅O₁₉·9H₂O has been synthesized and identified by chemical analysis and IR spectroscopy.     

Study of ionic equilibria and computation of thermodynamic characteristics of heteropoly anion formation in GdW10O 36 9− solution

Interaction in GdW₁₀O ₃₆ ^9? -H⁺(OH^?)-H₂O system ( \(C_{GdW_{10} O_{36}^{9 - } } \) = 1 × 10^?3 mol/L) was studied by pH potentiometry at 25 ± 0.1°C, and a model that describes equilibrium processes in acid and alkaline regions was selected. Logarithms of concentrational and thermodynamic constants, values of Gibbs energy of monomeric ions reactions, and standard Gibbs energies of formation (ΔG _f ^o ) of heteropoly anions H _n GdW₁₀O ₃₆ ^(9?n)? and H _m GdW₅O ₁₈ ^(3?n)? were calculated. A series-parallel scheme of ion transitions was pro-posed, ion distribution diagrams in aqueous solutions were built, the regions of preferable anion content were found, and heteropoly salts were synthesized.     

Crystal structure of (C2H7N4O)2[(UO2)2)(OH)2(C2O4)(CHO2)2]

An X-ray diffraction study of the single crystals of (C₂H₇N₄O)₂[(UO₂)₂(OH)₂(C₂O₄)(CHO₂)₂] was carried out. The compound crystallizes in the triclinic system, space group $P\bar 1$ , Z = 2, a = 5.5621(8) Å, b = 8.1489(10) Å, c = 11.8757(16) Å, α = 88.866(7)°, β = 82.204(6)°, γ = 87.378(6)°, V = 532.7(1) ų, ρ_calcd = 2.988 g/cm³. The main structural units in the crystal are the [(UO₂)₂(OH)₂(C₂O₄)(CHO₂)₂)]^2? chains corresponding to the crystal chemical group A₂M ₂ ² K⁰²M ₂ ¹ (A = UO ₂ ²⁺ , M² = OH^?, K⁰² = C₂O ₄ ^2? , M¹ = CHO ₂ ^? ) of uranyl complexes. The chains are united into a three-dimensional framework through the electrostatic interaction and hydrogen bonds involving uranyl, oxalate, and hydroxyl groups, formate ions, and 1-carbamoylguanidinium cations.     

The enthalpy of formation of natural siderophyllite

A thermochemical study of lithium siderophyllite (K_0.75Na_0.06Rb_0.01Ca_0.11)(Li_0.11Fe _1.25 ²⁺ Mn_0.02Mg_0.66Al_0.35Fe _0.23 ³⁺ Ti_0.18)[Si_2.53Al_1.47O₁₀](OH)_1.63F_0.37 (I) and siderophyllite (Al-Fe biotite) (K_0.89Na_0.04)(Fe _1.69 ²⁺ Mn_0.03Mg_0.20Al_0.59Fe _0.14 ³⁺ Ti_0.06)[Si_2.80Al_1.20O₁₀](OH)_0.80F_1.16Cl_0.04(II) was performed on a high-temperature Tian-Calvet microcalorimeter. Their enthalpies of formation from the elements, Δ_f H _el ^° (298.15 K) = ?5724 ± 12 (I) and ?5573 ± 14 (II) kJ/mol, were determined by melt solution calorimetry. The Δ_f G _el ^° (298.15 K) = ?5359 ± 12 (I) and ?5231 ± 14 (II) kJ/mol values were calculated. An increase in the content of iron in siderophyllite increased the entropy, enthalpy, and free energy of formation from the elements.