Thermal Decomposition Pathways Research Articles

Synthesis, Characterization, and Some Properties of Cp*W(NO)(H)(η(3)-allyl) Complexes.

Sequential treatment at low temperatures of Cp*W(NO)Cl2 in THF with 1 equiv of a binary magnesium allyl reagent, followed by an excess of LiBH4, affords three new Cp*W(NO)(H)(η(3)-allyl) complexes, namely, Cp*W(NO)(H)(η(3)-CH2CHCMe2) (1), Cp*W(NO)(H)(η(3)-CH2CHCHPh) (2), and Cp*W(NO)(H)(η(3)-CH2CHCHMe) (3). Complexes 1-3 are isolable as air-stable, analytically pure yellow solids in good to moderate yields by chromatography or fractional crystallization. In solutions, complex 1 exists as two coordination isomers in an 83:17 ratio differing with respect to the endo/exo orientation of the allyl ligand. In contrast, complexes 2 and 3 each exist as four coordination isomers, all differing by the orientation of their allyl ligands which can have either an endo or an exo orientation with the phenyl or methyl groups being either proximal or distal to the nitrosyl ligand. A DFT computational analysis using the major isomer of Cp*W(NO)(H)(η(3)-CH2CHCHMe) (3a) as the model complex has revealed that its lowest-energy thermal-decomposition pathway involves the intramolecular isomerization of 3a to the 16e η(2)-alkene complex, Cp*W(NO)(η(2)-CH2═CHCH2Me). Such η(2)-alkene complexes are isolable as their 18e PMe3 adducts when compounds 1-3 are thermolyzed in neat PMe3, the other organometallic products formed during these thermolyses being Cp*W(NO)(PMe3)2 (5) and, occasionally, Cp*W(NO)(H)(η(1)-allyl)(PMe3). All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses.

Thermal decomposition studies of bio-resourced polyamides by thermogravimetry and evolved gas analysis

In this work the degradation process of polyamides (PAs) based on renewable resources – PA 4.10, PA 6.10, PA 10.10 and PA 10.12, was studied by thermogravimetry (TG) coupled with evolved gas analysis (EGA) by infrared spectrophotometry (IR), quadrupole mass spectrometry (QMS).The TG/FTIR/QMS studies in inert atmosphere showed that the thermal decomposition of bio-polyamides takes place with the evolution of alkenes, nitriles, cyclic species and low molecular weight compounds – carbon monoxide, carbon dioxide, water and ammonia. The thermo-oxidative decomposition of bio-polyamides start with N-vicinal methylene group and follow with the scission of alkyl-amide or vicinal CC bond. The high energy reactions result in production of mainly low molecular gases (CO2, CO, H2O, NH3). Char residue analysis revealed the presence of carboxylic end groups, which may participate in secondary reactions during degradation, resulting in crosslinks, and decomposing to carbon dioxide. Taking into account the thermoanalytical results obtained, the thermal decomposition pathway for bio-polyamides in inert atmosphere has been postulated.

Aluminum, gallium and indium thiobenzoates: synthesis, characterization and crystal structures

Compounds R2M[S(O)CPh] [where R = tBu, M = Al (1); R = tBu, M = Ga (2); R = Me, M = Ga (3)] have been synthesized in reactions of R3M with thiobenzoic acid in a 1:1 molar ratio of reagents. The reaction of Me3Ga with three equivalents of thiobenzoic acid yielded the compound Ga[S(O)CPh]3 (4), in which thiobenzoate moieties act as bidentate SO ligands. In the presence of Et3N, InCl3 reacted with thiobenzoic acid with formation of an ionic compound {In[S(O)CPh]4}−(HNEt3)+ (5). The thiobenzoate ligands are bonded with the metallic center via the sulfur atoms only. The compounds 4 and 5 have been structurally and thermally studied. The thermal decomposition pathways of compounds 4 and 5 are proposed.

Vacuum thermal decomposition of polyethylene containing antioxidant and hydrophilic/hydrophobic silica

Temperature-programmed desorption mass spectrometry has been used to study vacuum thermolysis of high-density polyethylene (HDPE) and its composites with hydrophilic or hydrophobic nanosilica in the presence or absence of butylated hydroxytoluene (BHT). It has been found that both surface chemistry of silica filler and the presence of immobilized BHT affect the pathway of HDPE thermal decomposition. Volatility of BHT antioxidant was shown to decrease in the following sequence: free BHT > HDPE–BHT > HDPE–hydrophobic silica/BHT > HDPE–hydrophilic silica/BHT, and the capability of the additives to inhibit chain scission reaction during thermal decomposition of HDPE in vacuum was as follows: hydrophobic silica/BHT > BHT > hydrophobic silica > hydrophilic silica/BHT > hydrophilic silica ≈ no additives.

The investigation of thermal decomposition pathway and products of poly(vinyl alcohol) by TG‐FTIR

ABSTRACTA generalized form of a semiquantitative method has been developed based on the multilinear least‐squares regression technique applied on the entire FTIR absorbance spectrum of a gaseous mixture to determine components concentration. Thermal degradation of poly(vinyl alcohol) samples with high, PVA(98), and low degree of hydrolysis, PVA(80), has been investigated by TG‐FTIR simultaneous analysis performed in an inert atmosphere. Analysis of gaseous products was carried out using a routine developed in Matlab and this routine returns the product concentration with a reasonable RMS error. The correlation coefficients of the original mixture spectrum with the mixed output were obtained at some specific peak temperatures using irAnalysis software. The first process is the loss of physically adsorbed water which followed by two main processes of thermal degradation. In spite of the similarity of evolved gaseous products, two samples showed some differences in components concentrations identified in the volatile mixture. Acetaldehyde has been identified as the main volatile product in the first thermal degradation step of PVA(98) and PVA(80). The second major degradation product of PVA(80) is acetic acid due to presence of more residual acetate group while 2‐butenal have been identified for PVA(98). Water was mainly produced in the first stage of thermal degradation of PVA(98) while it was identified in the first and second stages for PVA(80). This might be attributed to existence of a competition between water and residual acetate group for elimination that postpones the complete elimination of OH group to the second degradation stage. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42117.

Controlled Synthesis of Layered Rare‐Earth Hydroxide Nanosheets Leading to Highly Transparent (Y0.95Eu0.05)2O3 Ceramics

Chemical precipitation at the freezing temperature of ~4°C has directly yielded layered rare‐earth hydroxide [LRH, Ln2(OH)5NO3·nH2O, Ln = Y0.95Eu0.05] nanosheets (up to 7 nm thick) for the Y/Eu binary system, with the interlayer NO3− exchangeable with SO42−. Calcining the sulfate derivative at 1100°C for 4 h produces well‐dispersed and readily sinterable Ln2O3 red phosphor powders (~14.8 m2/g) that can be densified into highly transparent ceramics via optimized vacuum sintering at the relatively low temperature of 1700°C for 4 h (average grain size ~14 μm; in‐line transmittance ~80% at the 613 nm Eu3+ emission or ~99% of the theoretical transmittance of Y2O3 single crystal). Our systematic studies also found that (1) the extent of SO42− exchange and the interlayer distance of LRH are both affected by the SO42−/Ln3+ molar ratio (R), and an almost complete exchange is achievable at R = 0.25 as expected from the chemical formula (one SO42− replaces two NO3− for charge balance). The optimal R value for sintering, however, was found to be 0.03; (2) The Ln3+ concentration for LRH synthesis substantially affects properties of the resultant oxides, and hard agglomeration has been significantly reduced at the optimized Ln3+ concentration of 0.05–0.075 mol/L; (3) Sulfate exchange significantly alters the thermal decomposition pathway of LRH, and was found essential to produce well‐dispersed and highly sinterable oxide powders; (4) Both the oxide powders and transparent ceramics exhibit the typical red emission of Eu3+ at ~613 nm (the 5D0→7F2 transition) under charge‐transfer (CT) excitation. Red‐shifted CT band center, stronger excitation/emission, and shorter fluorescence lifetime were, however, observed for the transparent ceramics.

Bimolecular decomposition pathways for carboxylic acids of relevance to biofuels.

The bimolecular thermal reactions of carboxylic acids were studied using quantum mechanical molecular modeling. Previous work1 investigated the unimolecular decomposition of a variety of organic acids, including saturated, α,β-unsaturated, and β,γ-unsaturated acids, and showed that the type and position of the unsaturation resulted in unique branching ratios between dehydration and decarboxylation, [H2O]/[CO2]. In this work, the effect of bimolecular chemistry (water-acid and acid-acid) is considered with a representative of each acid class. In both cases, the strained 4-centered, unimolecular transition state, typical of most organic acids, is opened up to 6- or 8-centered bimolecular geometries. These larger structures lead to a reduction in the barrier heights (20-45%) of the thermal decomposition pathways for organic acids and an increase in the decomposition kinetics. In some cases, they even cause a shift in the branching ratio of the corresponding product slates.

Thermal Decomposition of Nitropyrazoles

Fully nitrated five-membered heterocycles (pyrazoles), polynitropyrazoles in particular, have been actively studied as promising high-energy materials. Polynitropyrazoles have high density and high enthalpy of formation combined with reduced sensitivity to external stimuli. We have studied non-equilibrium processes of thermal decomposition of the first members of high-energy polynitropyrazoles row, i.e., 3,4–dinitropyrazole, 3,5–dinitropyrazole, and 3,4,5-trinitropyrazole, under atmospheric and increased pressures. The use of increased pressure allowed to reduce the influence of evaporation process of 3,5–dinitropyrazole and to determine the temperature and heat effect of its decomposition, which was found to exceed this value for HMX. For the first time evolved gas products were identified for each stage of decomposition. As a result the probable thermal decomposition pathway for the investigated materials was suggested.

Crystal structure and in situ decomposition of Eu(BH4)2 and Sm(BH4)2

Synthesis of halide free RE(BH4)2 (RE = Eu, Sm) complexes are detailed. Their crystal structures have been determined and thermal decomposition pathways studied by in situ SR-PXD and thermal analysis techniques.

Decomposition of diazomeldrum's acid: a threshold photoelectron spectroscopy study.

Derivatives of meldrum's acid are known precursors for a number of reactive intermediates. Therefore, we investigate diazomeldrum's acid (DMA) and its pyrolysis products by photoionization using vacuum ultraviolet (VUV) synchrotron radiation. The threshold photoelectron spectrum of DMA yields an ionization energy (IE) of 9.68 eV. Several channels for dissociative photoionization are observed. The first one is associated with loss of CH3, leading to a daughter ion with m/z = 155. Its appearance energy AE0K was determined to be 10.65 eV by fitting the experimental data using statistical theory. A second parallel channel leads to m/z = 69, corresponding to N2CHCO, with an AE0K of 10.72 eV. Several other channels open up at higher energy, among them the formation of acetone cation, a channel expected to be the result of a Wolff-rearrangement (WR) in the cation. When diazomeldrum's acid is heated in a pyrolysis reactor, three thermal decomposition pathways are observed. The major one is well-known and yields acetone, N2 and CO as consequence of the WR. However, two further channels were identified: The formation of 2-diazoethenone, NNCCO, together with acetone and CO2 as the second channel and E-formylketene (OCCHCHCO), propyne, N2 and O2 as a third one. 2-Diazoethenone and E-formylketene were identified based on their threshold photoelectron spectra and accurate ionization energies could be determined. Ionization energies for several isomers of both molecules were also computed. One of the key findings of this study is that acetone is observed upon decomposition of DMA in the neutral as well as in the ion and both point to a Wolff rearrangement to occur. However, the ion is subject to other decomposition channels favored at lower internal energies.

Alkali metal ion templated transition metal formate framework materials: synthesis, crystal structures, ion migration, and magnetism.

Four transition metal formate coordination polymers with anionic frameworks, namely, Na[Mn(HCOO)3], K[Mn(HCOO)3], Na2[Cu3(HCOO)8], and K2[Cu5(HCOO)12], were synthesized using a mild solution chemistry approach. Multitemperature single-crystal (100-300 K) and powder X-ray diffraction studies of the compounds reveal structures of large diversity ranging from cubic chiral Na-Mn formate to triclinic Na-Cu formate. The structural variety is caused by the nature of the transition metals, the alkali metal ion templation, and the versatility of the formate group, which offers metal-metal coordination through three different O-C-O bridging modes (syn-syn, syn-anti, anti-anti) in addition to metal-metal bridging via a single oxygen atom. The two manganese(II) compounds contain mononuclear, octahedrally coordinated moieties, but the three-dimensional connectivity between the manganese octahedra is very different in the two structures. The two copper frameworks, in contrast, consist of binuclear and mononuclear moieties (Na-Cu formate) and trinuclear and mononuclear moieties (K-Cu formate), respectively. Procrystal electron density analysis of the compounds indicates one-dimensional K(+)-ion conductivity in K-Mn and K-Cu, and the nature of the proposed potassium ion migration is compared with results from similar analysis on known Na(+) and K(+) ion conductors. K-Mn and Na-Mn were tested as cathode materials, but this resulted in poor reversibility due to low conductivity or structural collapse. The magnetic properties of the compounds were studied by vibrating sample magnetometric measurements, and their thermal stabilities were determined by thermogravimetric analysis and differential thermal analysis. Despite structural differences, the metal formates that contain the same transition metal have similar magnetic properties and thermal decomposition pathways, that is, the nature of the transition metal controls the compound properties.

Structure and stability of solid oligoglycines

Although peptides have been extensively studied within many disciplines, their solid state chemistry is not sufficiently explored. Crystalline peptide materials could present new opportunities in solid state organic synthesis as well as pharmaceutical, cosmetic and food industries. In order to facilitate these future applications, a better understanding of the relationship between the solid state structure and chemical reactivity in peptide crystals is required. In this work, a series of linear glycine oligomers was studied to see how their crystal structure and thermal reactivity changes with the chains growth. Single crystals of tetra- and pentaglycines were grown from aqueous solutions and investigated with XRD analysis (see Figure for pentaglycine). The newly collected data together with those reported previously reveal general trends likely present throughout all glycine oligomers. An antiparallel, hydrogen bound, β-sheet-like structure exists throughout the whole series and is the most stable polymorphic form in higher oligomers. Further, the thermal reactivity of this series was studied using gas chromatography – mass spectrometry (GC-MS), thermal gravimetric analysis (TGA) coupled with IR spectroscopy, differential scanning calorimetry (DSC) and bulk oven heating regimes. Finally 1H and 13C NMR and XRD analysis were used to identify key components of the thermal decomposition pathways as well as new products discovered during the thermal treatment. The results from all these studies suggest that the thermal stability of the oligomers increases with the chain length, but the decomposition pathways for the series are similar. In all cases, 2,5-diketopiperazine was formed through either condensation reactions (glycine and diglycine[1]) or depolymerisation of the peptide chain[2] in parallel with competing decomposition mechanisms. 2,5-Diketopiperazine and its derivatives are important biologically active molecules, and if this trend holds for other peptide oligomers, this solid state reaction could form a new, widely applicable synthetic method.

Molecular dynamics simulation on thermal decomposition mechanism of CL-20with different polymorphs

The initial thermal decomposition pathways of the supercell structures of e, β and γ modifications at different temperatures were studied by molecular dynamics simulations, using the ReaxFF force field, the NPT and NVT ensembles and the Berendsen methods.The results show that the initial pathway of different CL-20polymorphs is only the N-NO2dissociation to forming·NO2radical fragments, and the main thermal decomposition products are N2, H2O, CO, CO2, NO2, NO3, HNO2, HNO3, N2O5, N2O2and NO.The reaction rate constants of main products with the same modification increase with the increasing of temperature.

Development of a ReaxFF Reactive Force Field for Ammonium Nitrate and Application to Shock Compression and Thermal Decomposition

We have developed a new ReaxFF reactive force field parametrization for ammonium nitrate. Starting with an existing nitramine/TATB ReaxFF parametrization, we optimized it to reproduce electronic structure calculations for dissociation barriers, heats of formation, and crystal structure properties of ammonium nitrate phases. We have used it to predict the isothermal pressure-volume curve and the unreacted principal Hugoniot states. The predicted isothermal pressure-volume curve for phase IV solid ammonium nitrate agreed with electronic structure calculations and experimental data within 10% error for the considered range of compression. The predicted unreacted principal Hugoniot states were approximately 17% stiffer than experimental measurements. We then simulated thermal decomposition during heating to 2500 K. Thermal decomposition pathways agreed with experimental findings.

Theoretical studies on the dissociation reactions of chloromethyl peroxynitrate

Using the CCSD(T)/cc-pVDZ//B3LYP/6-311G(2d,2p) method, we investigated the detailed potential energy surfaces for the unimolecular dissociation reactions of chloromethyl peroxynitrate (CH2ClO2NO2). The results show that there are four most stable isomers of CH2ClO2NO2, named IS1, IS2, IS3 and IS4. From these isomers, twenty unimolecular decomposition reaction channels have been studied and discussed. Among them, the predominant thermal decomposition pathways are those direct O–N bond rupture to produce o-cis-CH2ClO2∗+NO2 or i-cis-CH2ClO2∗+NO2. The corresponding O–N bond dissociation energies (BDEs) are 22.0, 22.0, 21.7 and 21.7kcal/mol, respectively, in good agreement with the experimental results.

Synthesis and Characterization of Binary and Ternary Dioxouranium (VI) Complexes with Oxygen, Nitrogen and Sulphur Donor Ligands

Mononuclear binary and ternary complexes of UO22+ ion with N-salicylidene-4-Aminotoluene-3-sulfonic acid as primary ligand and 8-hydroxyquinoline as coligand have been prepared. The elemental analysis, molar conductance, IR and solid reflectance spectra in addition to the magnetic moment measurements, thermal study, XRD and SEM analysis were utilized to investigate the coordination behavior of these complexes. From the investigation data, all complexes have metal to ligand ratio of 1:1 and 1:1:1 with octahedral and dodecahedral geometry for binary and ternary complexes, respectively and the force constant, FU-O and bond length, RU-O were calculated. The thermal behavior of these complexes was investigated and the thermal decomposition pathways have been postulated showing that the final product is metal or metal oxide. Antimicrobial properties of the complexes have also been examined against Staphylococcus aureus (ATCC 25923), Streptococcus pyogenes (ATCC 19615), Pseudomonas fluorescens (S 97), Pseudomonas phaseolicola (GSPB 2828), Fusarium oxysporum and Aspergillus fumigatus. The corrosion inhibition of aluminum specimens in acidic solution was studied by weight loss method. The ternary complex, [UO2(HL)(8-Oqu)H2O] was found to be exhibits excellent inhibitory activity against the different microorganisms in addition to its corrosion inhibition efficiency towards Al-specimens in acidic solution more than the binary complex, [UO2(HL)NO3].2H2O.

Oxygen-Release-Related Thermal Stability and Decomposition Pathways of LixNi0.5Mn1.5O4 Cathode Materials

The thermal stability of charged cathode materials is one of the critical properties affecting the safety characteristics of lithium-ion batteries. New findings on the thermal-stability and thermal-decomposition pathways related to the oxygen release are discovered for the high-voltage spinel LixNi0.5Mn1.5O4 (LNMO) with ordered (o-) and disordered (d-) structures at the fully delithiated (charged) state using a combination of in situ time-resolved X-ray diffraction (TR-XRD) coupled with mass spectroscopy (MS) and X-ray absorption spectroscopy (XAS) during heating. Both o- and d- LixNi0.5Mn1.5O4, at their fully charged states, start oxygen-releasing structural changes at temperatures below 300 °C, which is in sharp contrast to the good thermal stability of the 4V-spinel LixMn2O4 with no oxygen being released up to 375 °C. This is mainly caused by the presence of Ni4+ in LNMO, which undergoes dramatic reduction during the thermal decomposition. In addition, charged o-LNMO shows better thermal stability than...

Thermal behavior of tetradentate Schiff base chromium(III) complexes

Thermal analytical behavior of eight chromium(III) complexes with N,N′-bis(salicylidene)ethylenediamine (salen) Schiff bases, Cr(salen), has been investigated regarding their thermal stability and thermal decomposition pathways. Thus, the ligands and the respective chromium(III) complexes of salen-type Schiff bases derived from salicylaldehyde and its 5-chloro, 5-bromo, 5-methoxy, 5-nitro, 3,5-dicloro, 3,5-dibromo, and 3,5-diiodosalicylaldehyde were synthesized, characterized, and submitted to TG/DTG, DTA, and TG–FTIR evolved gas analysis. The number of steps and, in particular, the starting temperature of decomposition of these complexes was dependent of the ligand nature. The gaseous products evolved during the thermal decomposition of these compounds were identified by TG–FTIR.

Ab initio studies of isomerization and dissociation reactions of methyl peroxynitrate

Using the CCSD(T)/cc-pVDZ//B3LYP/6-311G(2d,2p) method, we calculated the detailed potential energy surfaces (PESs) for the unimolecular isomerization and decomposition of methyl peroxynitrate (CH3O2NO2). The results show that there are the two most stable isomers, IS1a and IS1b, which are a pair of mirror image isomers. From IS1a and IS1b, different isomerization and unimolecular decomposition reaction channels have been studied and discussed. Among them, the predominant thermal decomposition pathways are those leading to CH3O2 + NO2 and cis-CH3ONO + O2. The former is the lowest-energy path through the direct O–N bond rupture in IS1a or IS1b. The PES along the O–N bond in IS1a has been scanned, where the energy of IS1a reaches maximum value of 23.5 kcal/mol when the O–N bond is stretched to about 2.8 A. This energy is 2.7 kcal/mol larger than the O–N bond dissociation energy (BDE) and 2.8 kcal/mol larger than the experimental active energy. In addition, because the energy barriers of IS1a isomerization to IS2a are 23.8 kcal/mol, close to the 20.8 kcal/mol O–N BDE in IS1a or IS1b, the isomerization reaction may compete with the direct bond rupture dissociation reaction.

Vibrational Spectra and Fragmentation Pathways of Size-Selected, D2-Tagged Ammonium/Methylammonium Bisulfate Clusters

Particles consisting of ammonia and sulfuric acid are widely regarded as seeds for atmospheric aerosol nucleation, and incorporation of alkylamines has been suggested to substantially accelerate their growth. Despite significant efforts, little direct experimental evidence exists for the structures and chemical processes underlying multicomponent particle nucleation. Here we are concerned with the positively charged clusters of ammonia and sulfuric acid with compositions H(+)(NH3)m(H2SO4)n (2 ≤ m ≤ 5, 1 ≤ n ≤ 4), for which equilibrium geometry structures have been reported in recent computational searches. The computed harmonic vibrational spectra of such minimum energy structures can be directly compared with the experimental spectra of each cluster composition isolated in the laboratory using cryogenic ion chemistry methods. We present one-photon (i.e., linear) infrared action spectra of the isolated gas phase ions cryogenically cooled to 10 K, allowing us to resolve the characteristic vibrational signatures of these clusters. Because the available calculated spectra for different structural candidates have been obtained using different levels of theory, we reoptimized the previously reported structures with several common electronic structure methods and find excellent agreement can be achieved for the (m = 3, n = 2) cluster using CAM-B3LYP with only minor structural differences from the previously identified geometries. At the larger sizes, the experimental spectra strongly resemble that observed for 180 nm ammonium bisulfate particles. The characteristic ammonium- and bisulfate-localized bands are clearly evident at all sizes studied, indicating that the cluster structures are indeed ionic in nature. With the likely (3,2) structure in hand, we then explore the spectral and structural changes caused when methylamine is substituted for ammonia. This process is found to occur with minimal perturbation of the unsubstituted cluster. The thermal decomposition pathways were also evaluated using multiple-photon induced dissociation and are, in all cases, dominated (>100:1) by evaporation of a neutral ammonia molecule rather than methylamine. Spectra obtained for the product cluster ions resulting from this evaporation are consistent with the formation of a single hydrogen bond between two neighboring bisulfate ions, partially regenerating a sulfuric acid molecule. These results provide critical experimental benchmarks for ongoing theoretical efforts to understand the early stages of aerosol growth.