Kinetics of the thermal decomposition of trans-1,2-dicyanocyclobutane

The kinetics of the thermal decomposition of trans-1,2-dicyanocyclobutane, which yields only vinyl cyanide, have been studied in the temperature range of 570°-660°K using a stirred-flow reactor. The reaction was found to be first order and homogeneous with rate constants represented by the Arrhenius equation where θ = 2.303 RT kcal/mol. The Arrhenius parameters are considerably higher than previously reported. On the assumption of a biradical mechanism the results are consistent with a cyano stabilization energy of ～5 kcal/mol, in good agreement with the results of recent studies of related systems.     

Investigations on the thermal decomposition of 1,2-dioxetanes via DSC

Reproducible measurements, reliable results and 1^st order kinetics for the whole reaction are obtained during the thermal decomposition of dioxetanes only, if inclusions of impurities in commercial sample pans are blocked by additional thick (magnitude of 100 ?m) and close Al₂O₃ protective layers. As a rule, nearly the same activation parameters are then found both for the decomposition of solvent-free dioxetanes and diluted solutions in several solvents. Mixtures of different dioxetanes in the same solvent contribute independently to the overall heat flow rate.

     

Stereospecific deoxygenation of 1,2-diols to olefins

The 2-dimethylamino-1,3-dioxolane derivatives of 1,2-diols when treated with trifluoromethane sulfonic anhydride and diisopropylethylamine in toluene give the corresponding olefins stereospecifically under mild experimental conditions.     

Regiospecific thermal C-acylation of imidazo [1,2-a] pyridines via an N-acylimidazolium intermediate

Direct acylation of imidazo [1,2-a] pyridines in a sealed tube at 130°C and without catalyst gave various 3-acyl derivatives in satisfactory yields.     

Effects of olefins on the thermal decomposition of propane part III. Some remarks on the kinetics of decomposition

Conditions of applicability of quasi-steady-state kinetic treatment have been investigated with respect to the explanation of the decomposition of propane and the influence of ethylene on this. From the measured rate of accumulation of ethane and from the relations between the kinetic equations describing product formation, the rate parameters of the initiation reactions were determined, for which the temperature-dependences and were found. In the decomposition of propane under the examined conditions, the chain length exceeds 500. In response to ethylene the chain length significantly decreases, but even in this case the decomposition chains are long enough for it to be assumed that the ratios of radical concentrations are governed by the propagation steps. Calculations demonstrated that the actual radical concentration during a sufficiently short induction period approximates to the stationary concentration, so that it does not seriously affect the accuracy of the kinetic treatment.     

Kinetics of the thermal decomposition of 1,2-dioxaspiro[2,5]octane

The products and kinetics of the thermolysis of 1,2-dioxaspiro[2,5]octane in cyclohexanone and cyclohexanone-CCl₄ mixtures are studied. 1,2-Dioxaspiro[2,5]octane is consumed via two parallel routes: isomerization to oxepan-2-one and solvent (cyclohexanone) oxidation with the partial escape of radicals from the cage (17% at 25 °C). Under an inert atmosphere, the alkyl radicals formed by solvent oxidation initiate the chain radical decomposition of 1,2-dioxaspiro[2,5]octane. The mechanism of 1,2-dioxaspiro[2,5]octane thermolysis is discussed on the basis of the results obtained. The activation parameters of 1,2-dioxaspiro[2,5]octane isomerization to oxepan-2-one and reactions of dioxaspiro[2,5]octane with cyclohexanone are discussed.     

Effect of olefins on the thermal decomposition of propane part I. The model reaction

Study of the thermal decomposition of propane at very low conversions in the temperature range 760–830 K led to refinement of the mechanism of the reaction. The quotient V/V characterizing the two decomposition routes connected with the 1- and 2-propyl radicals proved to depend linearly on the initial propane concentration. This suggested the occurrence of intermolecular radical isomerization: in competition with decomposition of the 2-propyl radical: The linearity led to the conclusion that the selectivity of H-abstraction from the methyl and methylene groups by the methyl radical is practically the same as that by the H atom. The temperature-dependence of this selectivity ( μ = kCH₃/kCH₂) was given by Further evaluation of the dependence gave the Arrhenius representation for the ratio of the rate coefficients of the above isomerization and decomposition reactions. Steady-state treatment resulted in the rate equation of the process, comparison of which with measurements gave further Arrhenius dependences.     

Thermal analysis of prednicarbate and characterization of thermal decomposition product

In the present work, the thermal behavior of prednicarbate was studied using DSC and TG/DTG. The solid product remaining at the first decomposition step of the drug was isolated by TG, in air and N₂ atmospheres and was characterized using LC-MS/MS, NMR, and IR spectroscopy. It was found that the product at the first thermal decomposition step of prednicarbate corresponds to the elimination of the carbonate group bonding to C₁₇, and a consequent formation of double bond between C₁₇ and C₁₆. Structure elucidation of this degradation product by spectral data has been discussed in detail.     

A mild procedure for the conversion of 1,2-diols to olefins

An improved procedure for the stereospecific synthesis of olefins from 1,2-diols via the corresponding thionocarbonate is described.     

Barium titanate via thermal decomposition of Ba,Ti-precursor complexes: The nature of the intermediate phases

The thermal decomposition of Ba,Ti-precursor complexes, containing organic ligands and suitable for the single-source preparation of nanocrystalline BaTiO₃, leads firstly to the segregation of specific Ba-rich and Ti-rich phases. Quantitative electron energy loss spectroscopy and powder X-ray diffraction data indicated that the (i) Ba-rich phase is a BaO-stabilised variant of the calcite-type high-temperature modification of BaCO₃ and (ii) Ti-rich phases are represented by low crystalline barium titanates with the general Ba:Ti ratio close to 1:4. The subsequent solid state reaction between these phases results then in the formation of BaTiO₃.     

Phase evolution of a barium tin 1,2-ethanediolato complex to barium stannate during thermal decomposition

The thermal behaviour of [Ba(C₂H₆O₂)₄][Sn(C₂H₄O₂)₃] used as a BaSnO₃ precursor, and its phase evolution during thermal decomposition are described. The initially formed transient barium tin oxycarbonate phase disintegrates into BaCO₃ and SnO₂, reacting subsequently to BaSnO₃. The existence of the intermediate oxycarbonate phase is evidenced by Fourier transformed infrared (FT-IR), X-ray powder diffraction (XRD) and electron energy loss spectroscopy (EELS (ELNES)) investigations.     

Synthesis of lead metaniobate by thermal decomposition of a coprecipitation product

The paper reports a new, nonconventional method for the preparation of oxygen-containing niobium compounds, based upon coprecipitation. The coprecipitation product of niobic acid with lead oxalate was used as precursor. Lead metaniobate was obtained by proper thermal treatment of the coprecipitate. The coprecipitate mechanism was studied and the optimal conditions for quantitative precipitation of niobium and lead were established. The mechanism of thermal decomposition of the coprecipitate was investigated by differential thermal analysis and X-ray powder diagrams. The final product of thermal decomposition, lead metaniobate, is formed at 850°C.     

Synthesis of calcium metaniobate by thermal decomposition of a coprecipitation product

The paper presents a new, nonconventional method, based upon coprecipitation, for the synthesis of niobium oxidic compounds. The coprecipitation product of niobic acid with calcium oxalate was used as precursor. Calcium metaniobate was obtained by appropriate thermal treatment of the coprecipitate. The coprecipitation mechanism was studied and the optimal conditions for quantitative precipitation of niobium and calcium were established. The mechanism of thermal decomposition of the coprecipitate was investigated by means of differential thermal analysis and X-ray powder diagrams. The final product of thermal decomposition, calcium metaniobate, is formed at 730°C.     

A product of the thermal decomposition of mixed hydroxides of calcium and titanium

Re-examination of the X-ray powder diffraction data obtained from a compound in the CaOTiO₂ system, reported to be Ca₂Ti₅O₁₂, suggests that the compound is a hitherto unknown defect pyrochlore of composition Ca₂Ti₂O₆. The lattice parameter is 9.953 ± 0.002 Å.     

Thermal decomposition of ammonia. N2H4-an intermediate reaction product

The paper reports the thermal decomposition of ammonia under dynamic conditions at 800°C in a quartz reactor. Its purpose is to confirm the homogeneous-heterogeneous degenerated branched chain mechanism established in previous studies, which assume the formation of N₂H₄ as a molecular intermediate; this paper identifies hydrazine as a product of thermal decomposition using FT-IR and UV-VIS spectroscopies.     

Mass spectra of methylsubstituted monosila- and monogermacyclobutanes, 1,2- disila- and 1,2-digermacyclopentanes. Some correlations with thermal decomposition

The mass spectra of 1,1-dimethyl-1-silacyclobutane (I—as reported by Cherniak et al.),⁶, 1,1-dimethyl-1-germacyclobutane (II), 1,1,2,2-tetramethyl-1,2-disilacyclopentane (III) and 1,1,2,2-tetramethyl-1,2-digermacyclopentane (IV) are compared and some correlations between electron-impact fragmentation and thermal decomposition are derived. The mass spectra of the germanium compounds with respect to the silicone compounds are enriched by light fragment ions and exhibit lower intensities of odd-electron ions. The composition of some ions and apparently of neutral fragments coincides with that of the unstable intermediates which are suggested in the thermal decomposition mechanism of some related compounds. The loss of C₂H₄ is more characteristic under electron-impact as well as in thermal decomposition of Si-compounds, while C₃H₆ is preferable eliminated by the Ge-compounds.