Nucleation and crystal growth in Na2O · 2 CaO · 3 SiO2 glass: a DTA study

The non-isothermal devitrification of Na₂O · 2 CaO · 3 SiO₂ glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, T_m, and the activation energy values, E_c, for crystal growth.The temperature, T_m=580°C, is very close to the glass transition temperature, T_g=570°C, and the value of E_c=78 Kcal mole^?1 for the surface crystal growth is nearly the same as the value E_c=89 kcal mole^?1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped.     

Thermodynamics of the lanthanum-hydrogen system at 917°K

The binary system lanthanum-hydrogen has been studied at pressures up to 1 atm at 917°K by a calorimetric-equilibrium method. From the calorimetric measurements we found the enthalpy of formation of LaH₂ at 917°K to be ?45.7 kcal mole^?1 with an estimated uncertainty at ±0.3 kcal mole^?1. This result is about 4 kcal mole^?1 less negative than the values derived indirectly from plateau pressure equilibrium measurements by Mulford and Halley and by Korst and Warf. A comparison between the calorimetric and equilibrium measurements at 917°K provides information on the partial entropy of hydrogen in lanthanum and in the dihydride LaH_2±δ. The excess entropy of hydrogen in lanthanum is about 6 cal K^?1 mole^?1 at 917°K: this value is essentially fully accounted for by the estimated vibrational entropy contribution of the hydrogen atoms. In LaH_2±δ the partial entropy of hydrogen changes from small negative values at X ≈ 1.95 to positive values for X > 2. This entropy change is explained by an assumed intrinsic disorder of hydrogen in LaH₂ of about 0.02.     

Determination of kinetic parameters for the reaction between phenol and formaldehyde by differential scanning calorimetry

The kinetic parameters of the complex reaction between phenol and formaldehyde in the presence of sodium hydroxide (NaOH) have been obtained by differential scanning calorimetry (DSC). The two dominant reactions appear to be addition of formaldehyde to phenol with formation of o-hydroxymethyl-phenol and subsequent condensation of the latter. For both reactions, the activation energy (E_a), reaction order and rate constants at different temperatures have been determined. E_a for addition changes from 23·7 to 19·3 kcal mole^?1 and for condensation from 22·9 to 19·1 kcal mole^?1 when the amount of NaOH is increased from 0·25 to 1·00 per cent. The reaction order for addition is 2 and for condensation 1. Thus DSC appears useful for studying the kinetics of more complex polymerization reactions.     

1,2-oxazine chemistry—IV : The conformational equilibria in 2,5- and 2,4-dimethyltetrahydro-1,2-oxazines

The synthesis of 2,5-dimethyltetrahydro-1,2-oxazine via 5-methyldihydro-1,2-oxazine and the preparation of a pure sample of 2,4-dimethyltetrahydro-1,2-oxazine are reported. For the 2,5-dimethyl derivative low temperature (?40° to ?45°) ¹H NMR measurements show signals from the trans (95%) and cis (5%) conformations. From this result it follows that an axial 5-Me group in a tetrahydro-1,2-oxazine ring is 5·7 ± 0·4 kJ mole^?1 less stable than when equatorial. Low temperature measurements on the 2,4-dimethyl derivative fail to show any sign of the conformation with an axial Me group. These results in conjunction with earlier relative free energy difference measurements, give the following conformational free energy differences for Me groups on ring C atoms; C(4) 7·1 ± 1·0; C(3) 7·9 ± 0·8; C(6) 10·1 ± 1·6 kJ mole^?1.     

Applications of carbon-13 resonance spectroscopy—XV : The degenerate cope-rearrangement of bullvalene

The temperature dependence of the ¹³C-NMR spectrum of bullvalene has been studied from ?67 to +128°C using fourier transform spectroscopy and ¹H broadband decoupling. Lineshape analysis based on the Anderson-Kubo-Sack theory yielded E_a=13·9±0·1 kcal/mole, log A= 14·0±0·1, ΔH3 = 13·3±0·1 kcal/mole, and ΔS3 = 3·4±0·4 e.u. The pertinent features of dynamic ¹³C-NMR spectroscopy are discussed.     

Etudes calorimetriques en milieu solvant organique. V. Enthalpies de dissolution de l'alanate de sodium,NaAlH4, dans le tetrahydrofuranne

The enthalpies of dissolution of sodium tetrahydridoaluminate NaAlH₄ in THF have been determined for different concentrations. The enthalpies of dissolution and dilution are exothermic from 1 to 7 · 10^?3 M. The enthalpy of dissolution at infinite dilution has been calculated: ΔH^∝_diss = ?6.38 kcal mole^?1.     

Thermochemical studies of sym-dichlorobis (2,4,6-trichlorophenyl) urea

Thermal decomposition of sym-dichlorobis (2,4,6-trichlorophenyl) urea occurs by two steps: the first at 150–184°C accompanied by a 26% weight loss and +(16.6±0.7) kcal mole^?1 and the second by a 40% weight loss and ?(17.4±1.0) kcal mole^?1. The decomposition pressure follows the equation ln p=A + B/T + C/T² where A = 149.89, B=9.45·10 [4] and C=1.48·10 [7]. The decomposition products are 2,4,6-trichlorophenyl isocyanate 2,4,6-trichloroaniline, chlorine, 1,2,3,5-tetrachlorobenzene, 2,2′,4,4′,6,6′-hexachlorobiphenyl, 2,2′,4,4′-tetrachlorobiphenyl, 2,2′,4,4′,6-pentachlorobiphenyl and ammonium chloride.     

Mass spectrometric evidence for the very high stability f gaseous ThIr and ThPt and method of calculating dissociation energies of diatomic intermetallic compounds with multiple bonds

The dissociation energes, D⁰₀, of the molecules ThIr and ThPt have been measured by high temperature Knudsen cell mass spectrometry as 136.4=10 and 130.7=10 kcal mole^?1 or 570.7±41.8 and 546.6±41.8 kJ mole^?1, respectively.A method is proposed for the calculation of dissociation energies of gaseous intermetallic compounds with multiple bonds.     

Zur Thermochemie der Verbindung Ba(NO3)2·2 KNO3

From the heats of solution for Ba(NO₃)₂ (c), KNO₃ (c; II), and Ba(NO₃)₂ · 2 KNO₃ (c) the heat of combination of the double salt from its component salts ΔH ₂₉₈ ⁰ =(?2.168±0.028) kcal · mole^?1 and the standard heat of formation ΔH _f,298 ⁰ =?474.75 kcal · mole^?1 have been determined. The values of derived thermodynamic properties are summarized in table 4.     

Conformational analysis of intramolecular bonded amino alcohols : The conformational free energies of some intramolecular OH ⋯ N hydrogen bonds

Equilibrium positions between intramolecular OH ? N hydrogen bonded and free OH forms of some 3-piperidinols, decahydroisoquinolinols, a decahydroquinolinol, lupinine and N-methyl-3-piperidinemethanol have been determined from dilute solution IR spectral data at 33°. Conformational free energies of the H-bonds (ΔG°_OH?N, attractive) have been calculated. The results suggest a linear relationship between the apparent value of ΔG°_OH?N, as defined by the method of calculation, and the strength of the OH ? N bond expressed as Δν, within the limits of 0·5 ± 0·2kcal/mole per 100 cm^?1, from Δν 90 to 350 cm^?1. For cis-decahydroisoquinoline (N-Me or N-H) systems, a 0·4 kcal/mole difference has been calculated between the two possible ring-fused conformations, in favor of the so-called steroid form. For the corresponding cis-decahydroqumoline equilibrium, a 0·8 kcal/mole difference has been calculated, in favor of the nonsteroid form.     

Kinetic Study of Cationic Polymerization of α-Methylstyrene Initiated by BuOTICl3 In Dlchloromethane Solution

The cationic polymerization of α-methylstyrene Initiated by n-BuOTiCl₃ has been studied at -70° C in dlchloromethane solution by using a calorlmetric technique. Polymerizations were performed under high vacuum either in dry conditions for which low monomer conversions were observed (4-12%), or In the presence of added cocatalyst (H₂O or HCl). In these last cases, yields were quantitative, and it was shown that polymerization rate was proportional to added water concentration and first order with respect to catalyst and to monomer. A kinetic scheme is proposed, based on a monomer-Independent initiation step and on a unimolecular termination process. At -70° C, the initiation rate is higher than termination rate during the whole course of the polymerization, and the concentration of active centers increases continuously. The following rate constants were found at -70°C: k_i. = 17 ± 6, k = 2.2 ± 1.1 ± 10⁴,k_trm = 30 ± 15 liter/mole-Sec, and k_t =0 54 ± 0 05 sec^?1. At -50 and -30° C, the concentration of active centers goes through a maximum during the polymerization and incomplete monomer conversions were observed, showing that all the catalyst is consumed. The different rate constants were tentatively estimated at these temperatures by using a simulation method, and this led to a negative value of ca. -7 kcal/mole for the apparent activation energy for propagation, and to a value of ～ 5 kcal/ mole for E_i. The observation of a negative (E_p)_app might be explained either by a shift of the dissociation equilibrium of the growing ends or by a solvation process of these growing ends by monomer prior to the propagation step.     

An oxyluminescence investigation of the auto-oxidation of nylon 66

The kinetics of the thermal oxidation of stabilised and unstabilised nylon 66 fibres and films have been studied by photon counting oxyluminescence methods from 50°C to 150°C. The activation energies for initiation (E₁), propagation (E₃) and termination (E₅) over this temperature range are: E₁ = 16 kcal mol^?1, E₃ = 17·5 kcal mol^?1 and E₅ ≈ 12 kcal mol^?1. The extent of orientation of the polymer does not change the nature of the oxyluminescence curve or E₃ and E₅ above 110°C.Significant losses of critical mechanical properties of the fibres occur in the induction period at 100°C and non-stationary kinetics are described to enable this region to be studied by oxyluminescence. The oxidation rate in the induction period and the limiting rate region in air is one-third the rate in oxygen at atmospheric pressure. Non-stationary methods show that alkyl radical reactions are competitive with alkyl peroxy radical formation in air over the temperature range 100°C to 140°C. This affects the course of the oxidation reaction and the stabiliser efficiency and explains the observation of unsaturated oxidation products by phosphorescence spectroscopy.     

The fluorobasicities of ReF7 and IF7 as measured by the enthalpy change ΔH°(EF7(g) → EF6+(g) + F−(g))

Iridium hexafluoride oxidizes ReF₆ (via an ReF₆⁺ salt) and at room temperatures IrF₆, ReF₆, ReF₇ and (IrF₅)₄ are each present in the equilibrium mixture. From these and related findings: ΔH°(ReF₆ → ReF₆⁺ + e^?) 1092 ± 27 kj mole^?1(261 ± 6 kcal mole^?1), and thermodynamic data are selected to yield ΔH°(ReF_7(g) → ReF₆⁺_(g) + F^?_(g))=893 ± 33 kj mole^?1(213 ± 8 kcal mole^?1). From observations on the stability of IF₆⁺BF₄^? and the lattice enthalpy evaluation for the salt, ΔH°(IF_7(g) → IF₆⁺_(g) + F^?_(g))= 870 ± 24 kj mole^?1(208 ± 6 kcal mole^?1).     

Calorimetric studies on the thermal decomposition of tri n-butyl phosphate-nitric acid systems

Thermal decomposition of neat TBP, acid-solvates (TBP·1.1HNO₃, TBP·2.4HNO₃) (prepared by equilibrating neat TBP with 8 and 15.6?M nitric acid) with and without the presence of additives such as uranyl nitrate, sodium nitrate and sodium nitrite, mixtures of neat TBP and nitric acid of different acidities, 1.1?M TBP solutions in diluents such as n-dodecane (n-DD), n-octane and isooctane has been studied using an adiabatic calorimeter. Enthalpy change and the activation energy for the decomposition reaction derived from the calorimetric data wherever possible are reported in this article. Neat TBP was found to be stable up to 255?°C, whereas the acid-solvates TBP·1.1HNO₃ and TBP·2.4HNO₃ decomposed at 120 and 111?°C, respectively, with a decomposition enthalpy of ?495.8?±?10.9 and ?1115.5?±?8.2?kJ?mol^?1 of TBP. Activation energy and pre exponential factor derived from the calorimetric data for the decomposition of these acid-solvates were found be 108.8?±?3.7, 103.5?±?1.4?kJ?mol^?1 of TBP and 6.1?×?10¹⁰ and 5.6?×?10⁹?S^?1, respectively. The thermochemical parameters such as, the onset temperature, enthalpy of decomposition, activation energy and the pre-exponential factor were found to strongly depend on acid-solvate stoichiometry. Heat capacity (C _p ), of neat TBP and the acid-solvates (TBP·1.1HNO₃ and TBP·2.4HNO₃) were measured at constant pressure using heat flux type differential scanning calorimeter (DSC) in the temperature range 32?C67?°C. The values obtained at 32?°C for neat TBP, acid-solvates TBP·1.1HNO₃ and TBP·2.4HNO₃ are 1.8, 1.76 and 1.63?J?g^?1?K^?1, respectively. C _p of neat TBP, 1.82?J?g^?1?K^?1, was also measured at 27?°C using ??hot disk?? method and was found to agree well with the values obtained by DSC method.     

The nitric oxide catalyzed positional isomerization of 3-methylene-1,5,5-trimethylcyclohexene and the stabilization energy in the 3-methylenecyclohexenyl radical

The gas phase, nitric oxide catalyzed positional isomerization of 3-methylene-1,5,5-trimethylcyclohexene (MTC) into 1,3,5,5-tetramethyl-1,3-cyclohexadiene (TECD) has been studied for temperatures ranging between 296° and 425°C. The major reaction was first order with respect to nitric oxide and to MTC. The major side product, mesitylene, usually amounted to less than 10% of the TECD isomer formed. Only at high temperatures and large conversions has up to 20% been observed. Conditioned pyrex or quartz vessels coated with KCl have been used. The nitric oxide catalyzed isomerization is apparently a homogeneous process, as demonstrated by the insensitivity of the observed rate constants towards a 15-fold increase in the surface to volume ratio of the reaction vessels. However, a residual, presumably heterogeneous, thermal isomerization of the starting material could not be eliminated. Good mass balances were obtained for both NO and hydrocarbons. After correcting for the thermally induced conversion the observed rate constants for the nitric oxide catalyzed isomerization yield log k₁ (1 mole^?1 sec^?1) = (10.7 ± 0.2) – (37.3 ± 0.9)/θ where θ is 2.303 × 10^?3 RT (kcal mole^?1). Plotting log k₁ versus the ratio of the starting materials (MTC/NO)₀ it was found that for temperatures ≥ 365°C the rate constants were systematically too high. Using extrapolated values for the higher temperature range yields the more reliable corrected Arrhenius equation log k = 8.6 – 31.7/θ. The reaction mechanism is outlined and the implications with respect to the stabilization energy generated in the MTC? radical intermediate and the activation energy of the backreaction MTC? + HNO are discussed. Using for the activation energy E_?1 of the backreaction (R? + HNO) a literature value of 9.2 ± 0.9 kcal mole^?1 reported for the cyclohexadiene? 1,3? system, this yields 23.4 ± 2 kcal mole^?1 for the stabilization energy in the methylenecyclohexenyl radical, which is to be compared with the corresponding values for the allyl (10.2 ± 1.4), methallyl (12.6 ± 1) pentadienyl (15.4 ± 1) and cyclohexadienyl (24.6 ± 0.7) radicals. The pre-exponential factor agrees well with the value of (8.4 ± 0.2) reported by Shaw and co-workers for the similar reaction of NO with 1,3-cyclohexadiene. It is noteworthy that HNO, acting as sole hydrogen donor in the system, is surprisingly stable under the reaction conditions used. Nitrous oxide, HCN, H₂O and N₂ are observed in the product mixture of experiments carried out to high conversions at higher temperatures.     

Vaporization study of the SbBr3 system by the torsion—effusion method

Vapor pressures of solid antimony tribromide were measured by the torsion—effusion technique. The values obtained can be expressed by the equation log P(atm) = (9.3 ± 1.3) ? (4.4 ± 0.5)/T in the temperature range 324–368 K.The standard heat of vaporization was derived by second- and third-law treatment of the data and compared with values reported in the literature. The value ΔH⁰_vap (298 K) = 19.5 ± 0.5 kcal mole^?1 was derived.     

Equilibrium sublimation and thermodynamic properties of SnS

Knudsen effusion studies of the sublimation of polycrystalline SnS, prepared by annealing and chemical vapor transport, have been performed employing vacuum micro-balance techniques in the temperature range 733–944 K and at pressures ranging from about 6 × 10^?3 to 11 Pa.The third-law heats of sublimation and second-law entropy of reaction SnS(s) = SnS(g) were determined to be ΔH⁰₂₉₈ = 220.4 ± 3.0 kJ mole^? and ΔS⁰₂₉₈ = 162.4 ± 4.5 J K^?1 mole^?1. From these data the standard heat of formation and absolute entropy of SnS(s) were calculated to be ?102.9 ± 4.0 kJ mole^?1 and 79.9 ± 6.0 J K^?1, respectively.     

Kinetics of anionic polymerization of methylmetacrylate with caesium and sodium as counterions in tetrahydrofuran

The kinetics of the anionic polymerization of methylmethacrylate in tetrahydrofuran at ?75 are investigated. Cumylcaecium, α-methylstryrylcaesium and α-methylstyrylsodium were used as initiators. The results show that the polymerization proceeds practically without side reactions under these conditions; as for the anionic polymerization of styrene in polar solvents, ion pairs and anions contribute to the propagation. The rate constant of monomer addition to the ion pair has at ?75 values of 60 and 80 for polymethylmethacrylsodium and polymethylmethacrylcaesium, respectively, and for the anion about 5 × 10⁴ l mole^?1 sec^?1. The dissociation constant was measured as 3·5 × 10^?9 for polymethylmethacrylsodium and 2 × 10^?9 mole/l for the caesium compound at this temperature: the corresponding dissociation enthalpies are ?0·3 and ?1·3 kcal mole^?1. The relatively low activation energy for monomer addition to the ion pair of polymethylmethacrylsodium of 2·3 kcal mole^?1 suggests the existence of two types of ion pairs whereas the corresponding value for polymethylmethacrylcaesium of 4·5 kcal mole^?1 does not allow such an interpretation. The kinetic results are compared with those of the corresponding polystyrylcompounds: the differences are explained by the fact that, in the case of the polymethylmethacryl compound, the estergroup competes with the solvent for solvation of the cation.     

Vapor pressure measurements of ferrocene,mono- and 1,1′-di-acetyl ferrocene

By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 ? (3805 ± 46)/T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 ? (5916 ± 48)/T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 ? (4289 ± 44)/T By second- and third-law treatment of the vapor data the ΔH⁰_sub,298 = 74.0 ± 2.0 kJ mole^?1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values ΔH⁰_sub,298 = 115.6 ± 2.5 kJ mole^?1 and ΔH⁰_sub,298 = 91.9 ± 2.5 kJ mole^?1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.     

Zur Thermochemie von gasförmigem GeWO4 und GeW2O7

Thermochemistry of Gaseous GeWO₄ and GeW₂O₇ Mass spectrometric investigations with a Knudsen cell arrangement at temperatures between 1258 and 1383 K proved the existence of GeWO₄ and GeW₂O₇ as component of the vaporphase over a mechanical mixture of GeO₂ and WO₂. Using the partial pressures heats of formation (2nd law calculation) and entropies (3rd law calculation) were computed; i. e. GeWO₄: δH°₁₃₃₀ = ?149.8 kcal · mole^?1, S°₁₃₃₀ = 129.9 cal K^?1 mole^?1, GeW₂O₇: δH°_f,₁₃₃₀ = ?310.6 kcal mole^?1, S°₁₃₃₀ = 190.0 cal K^?1 mole^?1. The standard heats of formation and entropies at 298 K, calculated with estimated Cp values are: GeWO₄: δH°_f,₂₉₈ = ?181.6 kcal mole^?1, S°₂₉₈ = 85.0 cal K^?1 mole^?1; GeW₂O₇: δH°_f,₂₉₈ = ?365.8 kcal mole^?1, S°₂₉₈ = 112.1 cal K^?1 mole^?1. The thermochemical data of the GeWO₄ and GeW₂O₇ molecules which also appear at chemical transport experiments [2] with GeO₂ + WO₂, are compared with known gaseous tungstates.