Gas-phase thermolysis of benzotriazole derivatives. Part 2: Synthesis of benzimidazo[1,2-b]cinnolines, a novel heterocyclic ring system, by pyrolysis of benzotriazole derivatives. Kinetic and mechanistic study

Gas-phase pyrolysis of benzotriazolyl ketones and their arylhydrazones gave indole, benzimidazole and benzimidazo[1,2-b]cinnoline derivatives via interesting novel routes. The homogeneous first-order gas-phase pyrolysis of 10 arylhydrazono derivatives of α-benzotriazol-1-yl ketones was investigated over the temperature range 420-530 K. Five of these substrates were 2-(arylhydrazono)-2-(benzotriazol-1-yl)-1-phenylethanone derivatives (Series 1), and the remaining five were the corresponding acetone analogues (Series 2). The values of the Arrhenius frequency factor (log A/s⁻¹) for the pyrolysis of the compounds of Series 1 and 2 were, respectively, 12.27±1.44 and 9.07±1.20, while the values of the Arrhenius activation energy (E_a/kJ mol⁻¹) were 132.8±8.4 and 123.2±23.0, respectively. Besides, reaction pathways are offered to rationalize the kinetic results and to account for the products of pyrolysis of the substrates under study, namely: (i) extrusion of N₂ and formation of a 1,3-biradical reactive intermediate leading to substituted imidazoles (Series 1); (ii) intramolecular nucleophilic addition, cyclization and subsequent fragmentation with or without loss of H₂O/N₂ fragments (Series 1 and 2).     

Generation of color-controllable room-temperature phosphorescence via luminescent center engineering and in-situ immobilization

Materials with controllable luminescence colors are highly desirable for numerous promising applications, however, the preparation of such materials, particularly with color-controllable room-temperature phosphorescence (RTP), remains a formidable challenge. In this work, we reported on a facile strategy to prepare color-controllable RTP materials via the pyrolysis of a mixture containing 1-(2-hydroxyethyl)-urea (H-urea) and boric acid (BA). By controlling the pyrolysis temperatures, the as-prepared materials exhibited ultralong RTP with emission colors ranging from cyan, green, to yellow. Further studies revealed that multiple luminescent centers formed from H-urea, which were in-situ embedded in the B₂O₃ matrix (produced from BA) during the pyrolysis process. The contents of the different luminescent centers could be regulated by the pyrolysis temperatures, resulting in color-tunable RTP. Significantly, the luminescent center engineering and in-situ immobilization strategy not only provided a facile method for conveniently preparing color-controllable RTP materials, but also endowed the materials prepared at relatively lower temperatures with color-changeable RTP features under thermal stimulus. Considering their unique properties, the potential applications of the as-obtained materials for advanced anti-counterfeiting and information encryption were preliminarily demonstrated.     

Possibilities and pitfalls in analyzing (upgraded) pyrolysis oil by size exclusion chromatography (SEC)

The applicability of size exclusion chromatography (SEC) to analyze (upgraded) pyrolysis oil samples has been studied using model compounds, pyrolysis oils and hydrodeoxygenated pyrolysis oils. The assumptions needed for the conversion of the chromatogram to the M_w-distribution were validated. It was shown that the conversion of elution volume to molecular weight (based on polystyrene calibration curves) can introduce substantial errors in the prediction of the molecular weight. The conversion of RID response to W(log M) (as plotted on the y-axis of the M_w-distribution) is based on the assumption of a compound independent RID response factor and linear response to concentration. While the latter was shown to be true within the concentration range studied, the former was not true: the RID response factor depends on the type of (upgraded) pyrolysis oil. It was shown that within a single pyrolysis oil sample, the RID response for the low molecular weight fraction was a factor 3 lower than the high molecular weight fraction. Furthermore long term column fouling can influence SEC results that cannot be corrected with regular polystyrene recalibrations.Based on the results we recommend SEC not to be used as a quantitative method for characterization (upgraded) pyrolysis oil samples, but as a tool to compare (upgraded) pyrolysis oil samples, preferably prepared using incremental operating conditions and expected to have similar molecular composition. This work has further shown that (i) the ∫UVDdv/∫RIDdv ratio can be used as an indication of the sum of the relative aromaticity and conjugated double bond content for (upgraded) pyrolysis oil, and (ii) the negative peak area appearing in the low molecular weight part of the chromatogram can be used to estimate the water content of (upgraded) oil samples.     

Synthesis,odor characteristics and thermal behaviors of pyrrole esters

A novel approach for transesterification of methyl pyrrole-carboxylate with alcohols is reported. The transformation is performed with t-BuOK and a series of new pyrrole ester were obtained under the optimized conditions. The odor characteristics of the pyrrolyl esters were evaluated by GC–MS-O (gas chromatography-mass spectrometry-olfactometry). Among them, compounds of 4-isopropylbenzyl 1H-pyrrole-2-carboxylate (3d) and naphthalen-2-ylmethyl 1H-pyrrole-2-carboxylate (3 l) present nuts and almond-like aroma, respectively. The Py-GC/MS (pyrolysis–gas chromatography/mass spectrometry) approach was applied to evaluate the pyrolysis intermediates of the pyrrole esters in oxidative conditions. It clarified that 3d and 3 l occurred different degrees of pyrolysis throughout the pyrolysis temperature from 30 °C to 900 °C. In addition, the TG (thermogravimetry) and DSC (differential scanning calorimeter) approaches were applied to investigate at the thermal degradation process. They have good thermal stability under certain temperature according to the results of TG analysis.     

Pyrolysis of polypropylene: II. Kinetics of degradation

The kinetic law dα/dr=k(1-α)[1-(1-α)^2b]^1,2 proposed for the pyrolysis of polystyrene is shown to be valid for the pyrolysis of polypropylene taking into account only the percentage of isotactic polymer.As the experimental activation energy of 265 kJ mol^?1 is of the same order of magnitude the as the theoretical energy calculated by the equation E = 1 2 (E_ir-E_r)-E_r it can be concluded that the decomposition mechanism is governed by a depolymerization reaction as the principal products obtained are compounds with 3n carbon atoms.     

Gas-phase thermolysis of 1-acylnaphtho[1,8-de][1,2,3]triazines. Interesting direct routes towards condensed naphtho[1,8-de]heterocyclic ring systems

FVP pyrolysis of 1-acylnaphtho[1,8-de][1,2,3]triazines at 500 °C and 10⁻² Torr gave exclusively the corresponding 2-substituted naphtho[1,8-de][1,3]oxazines. The latter was also obtained by static pyrolysis but in lower yield along with the corresponding N-(naphthalen-1-yl)acylamides. The reaction was studied kinetically and mechanistically.     

Catalytic thermal decomposition of polyamides and polyurethanes mixed with acidic zeolites

The purpose of this work was to examine the pyrolysis products derived from zeolite–polyamide and zeolite–polyurethane mixtures prepared in different ratios in order to elucidate the chemical reactions taking place under pyrolysis of these polymers in the presence of acidic Y zeolites (ultra stabilized HY (HUSY) and NH₄NaY). Therefore 5:1, 3:1, and 1:1 ratios of zeolite and nitrogen-containing polymer (polyamides and polyurethanes) mixtures were pyrolysed at 500 °C in a micro-pyrolyser on-line coupled with GC/MS. The products and product distribution of zeolite–polymer mixtures indicate that the amount of catalysts significantly affects the pyrolysis product distribution. In case of zeolite–PA-6,6 1:1 mixtures hexanedinitrile is the main pyrolysis product indicating that the thermal decomposition of PA-6,6 via cis-elimination is enhanced. Main pyrolysis products of zeolite–PA-6 mixtures of 1:1 ratio are dihydro-azepine isomers that are the dehydrated derivatives of ɛ-caprolactam. Pyrolysis of 1:1 zeolite–PA-12 mixtures leads to the promoted formation of dehydrated cyclic monomer isomers (azacyclotrideca-dienes). For zeolite–PUR 1:1 mixtures it was concluded that MDI decomposition to N-containing aromatics is enhanced, while the polyester and polyether segments degrade to monomer type products and to aromatics. For all zeolite–polymer mixtures increasing ratio of catalysts leads to increased amount of aromatics (benzene and naphthalene compounds) and light unsaturated hydrocarbons, while the amount of main products of 1:1 mixtures decreases.     

Characterization of slow pyrolysis oil obtained from linseed (Linum usitatissimum L.)

This study presents the characterization of pyrolysis oil obtained from linseed (Linum usitatissimum L.) produced by slow pyrolysis in the maximum yield. The pyrolysis oil was analyzed to determine its elemental composition and calorific value. The chemical composition of the pyrolysis oil and fractions were investigated using chromatographic and spectroscopic techniques (¹H NMR, IR, and GC). The chemical class composition of the oil was determined by liquid column chromatographic fractionation. The oil was separated into pentane soluble and insoluble fractions by using pentane. The column was eluted successively with n-pentane, toluene and methanol to yield aliphatic, aromatic and polar fractions, respectively. The results of the adsorption chromatography of the oil showed that the pyrolysis oil consists of 88 wt% n-pentane soluble. The aliphatic, aromatic and polar fractions of oils obtained in slow pyrolysis are 30, 34, 36 wt%, respectively. The aliphatic and aromatic subtraction make up ∼64 wt% in slow pyrolysis oil. This seems to be more appropriate for the production of hydrocarbons and chemicals.     

Study on pyrolysis behaviors of L-tyrosine-based phthalonitrile resin

The pyrolysis behaviors of l-tyrosine-based phthalonitrile(TPN) resin were investigated by thermogravimetric-Fourier transform infrared spectrometry-mass spectrometry (TG-FTIR-MS) and Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The small molecules produced during pyrolysis process of TPN resin were tracked in real time by TG-FTIR-MS. The larger molecules (m/z > 40) from fast pyrolysis at 900 °C of the TPN resin using Py-GC/MS were identified. From TG-FTIR-MS and Py-GC/MS results, the production pathways of pyrolysis products such as CO₂, CO, NH₃, benzonitrile and phenol were analyzed. The possible pyrolysis mechanism of TPN resin under non-oxidizing gaseous environment was proposed. The results of this study provide the useful information for designing the molecular structure of l-tyrosine-based polymers which possessing high thermal stability.     

The co-pyrolysis of flame retarded high impact polystyrene and polyolefins

The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types of brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC–FID, GC–MS, and GC–ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS.     

Pyrolysis of Hailar lignite in an autogenerated steam agent

An in situ pyrolysis process of high moisture content lignite in an autogenerated steam agent was proposed. The aim is to utilize steam autogenerated from lignite moisture as a reactant to produce fuel gas and additional hydrogen. Thermogravimetric analysis revealed that mass loss and maximum mass loss rate increased with the rise of heating rates. The in situ pyrolysis process was performed in a screw kiln reactor to investigate the effects of moisture content and reactor temperature on product yields, gas compositions, and pyrolysis performance. The results demonstrated that inherent moisture in lignite had a significant influence on the product yield. The pyrolysis of L _R (raw lignite with a moisture content of 36.9 %, wet basis) at 900 °C exhibited higher dry yield of 33.67 mL g^?1 and H₂ content of 50.3 vol% than those from the pyrolysis of the predried lignite. It was also shown that increasing reaction temperature led to a rising dry gas yield and H₂ yield. The pyrolysis of L _R showed the maximum dry yield of 33.7 mL g^?1 and H₂ content of 53.2 vol% at 1,000 °C. The LHV of fuel gas ranged from 18.45 to 14.38 MJ Nm^?3 when the reactor temperature increased from 600 to 1,000 °C.     

Thermoanalytical investigation of the synthesis of pyrazine and bipyrazine via the pyrolysis of the bis(pyrazinecarboxylate)copper(II) complex

The pyrolysis of hydrated bis(pyrazinecarboxylate)copper(II) under an argon atmosphere proceeds via the loss of the water molecules at 84–95°C, ΔH=40.4 kJ (mol H₂O)^?1 followed by the thermal decomposition of the complex at 284–325°C, ΔH=97.0 kJ·mol^?1, yielding 0.72 mole of pyrazine, 0.28 mole of bipyrazine, and 2 mole of CO₂ per mole of complex.     

Preparation of ternary metal chalcogenide (M1-xFexS, M = Cd and Zn) nanocrystallites using single source precursors

M_1−xFe_xS (M = Cd, Zn) nanocrystallites were prepared by pyrolysis and solvothermal decomposition methods using [M(Aftscz)₂] and [M(AftsczH)₂Cl₂] (M = Cd, Zn and AftsczH = monoacetylferrocene thiosemicarbazone) as single source precursors. The M_1−xFe_xS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis and UV-Visible spectroscopy. XRD patterns show that the Cd_1−xFe_xS and Zn_1−xFe_xS nanocrystallites prepared by pyrolysis and solvothermal decomposition routes have hexagonal phase. TEM images show presence of spherical and spherical plate-like morphology of M_1−xFe_xS nanoparticles. M_1−xFe_xS nanoparticles obtained by solvothermal decomposition in ethylene glycol are found to be capped with ethylene glycol as evident from IR spectra.     

Quality control of Amazonian cocoa (<Emphasis Type="Italic">Theobroma cacao</Emphasis> L.) by-products and microencapsulated extract by thermal analysis

The mineralogical characterization and pyrolysis kinetics of raw oil shale from Moroccan Rif region and the corresponding bitumen-free material were investigated using various analytical techniques. The structural analysis results showed the siliceous character of mineral matrix and the presence of complex organic components in both oil shales studied. Non-isothermal pyrolysis kinetic measurements indicated that bitumen-free oil shale exhibits a single behavior pyrolysis in the oil-producing stage as compared to raw oil shale. The activation energies estimated by using isoconversional methods reveal that the pyrolysis reaction occurred by one-step kinetic process. The kinetic parameters, determined from a nonlinear fitting method using various kinetic models g(α) and iterative Kissinger–Akahira–Sunose energy calculations, reveal that the pyrolysis mechanism is well described by the nth order kinetics (Fn), with n = 1.071, for bitumen-free oil shale, and n = 1.550, for kerogen of raw oil shale. The mechanism of the whole pyrolysis process of raw oil shale seems not to be affected by the elimination of bitumen, but only some kinetic changes have been recorded in the reaction order mechanism. The process pyrolysis is represented by independent reactions and consequently considered as parallel processes. Besides, the thermodynamic functions of activated complexes (?S ^≠ , ?H ^≠ and ?G ^≠) were also calculated and the pyrolysis is found as non-spontaneous process in agreement with the thermal analysis data.     

Oxime-trimethylsilylation method for analysis of wood pyrolysate

Oxime-trimethylsilylation (TMS) method was applied to the analysis of wood pyrolysate. Quantitative determination of hydroxycarbonyls such as glycolaldehyde, which are important pyrolysis products of wood polysaccharide, is difficult as indicated by the gas chromatography–mass spectrometry (GC–MS) and ¹H NMR analysis of glycolaldehyde. Glycolaldehyde decomposed into formic acid and the unknown compound with molecular weight of 72 at the injector in its GC analysis. ¹H NMR analysis of glycolaldehyde in acetone-d₆ indicated the complex mixture with its dimerization products. Glycolaldehyde was quantified precisely as oxime-TMS derivative (E/Z-mixture) of the monomer by GC after oximation with hydroxylamine hydrochloride and the following trimethylsilylation with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). With this method, the other carbonyls such as furfural, 5-hydroxymethylfurfural and hydroxyacetone could also be determined as their oxime-trimethylsilylated derivatives. Furthermore, anhydrosugars such as levoglucosan and levomannosan in wood pyrolysate were also determined, simultaneously, as their TMS derivatives. Finally, oxime-TMS method is proposed as a quantification method of the pyrolysis products derived from wood polysaccharide.     

Comparison of the properties of the polyimides,polyamides and polyureas derived from 1-[(dialkoxyphosphinyl)-methyl]-2,4- and -2,6-diaminobenzenes and m-phenylenediamine

The physical and thermal properties of various phosphorus-containing polyimides, polyamides and polyureas based on 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes as well as of the corresponding common polymers derived from m-phenylenediamine were compared and correlated with their chemical structure. Differential scanning calorimetry (DSC) measurements showed that the introduction of the (dialkoxyphosphinyl) methyl groups in the polymers converted their endothermic pyrolysis under anaerobic conditions to exothermic or reduced the heat adsorbed during their pyrolysis. Thermogravimetric analysis (TGA) showed that the thermal stability of the polymers and the char yield formed during their pyrolysis were in the order polyureas < polyamides < polyimides. All phosphorylated polymers showed a lower degree of polymerization, a lower polymer decomposition temperature and formed higher char residue on pyrolysis than the corresponding common polymers.     

Thermal decomposition of methylene bridges and methyl groups at aromatic rings in phenol-formaldehyde polycondensates

Phenol-formaldehyde polycondensates which contain methyl (or ethyl) substituents at different positions on the phenolic rings and methylene bridges at ortho or ortho and para positions were investigated. The products of pyrolysis at 600° C were analysed and the amounts of the alkylbenzenes and alkylphenols were related to the structure of the polycondensate pyrolysed. Most of the monoaromatic pyrolysis products are alkylphenols. The same alkyl substituents occur in the alkylphenolic pyrolysis products at the same positions that were present in the macromolecule. Methyl substituents were also found at the positions of the methylene bridges of the polycondensate, but their amounts in the pyrolysis products proved to be considerably lower than those of the methylene bridges related to the aromatic rings in the macromolecule.The amount of alkylbenzenes is only a few percent of that of alkylphenols in the 600°C pyrolysate, but the occurrence of the substituents in the alkylbenzene pyrolysis products reflects well the presence of the substituents and methylene bridges in the macromolecule.     

Development of methodologies to determine aluminum, cadmium, chromium and lead in drinking water by ET AAS using permanent modifiers

In this work, methodologies were developed to determine aluminum (Al), cadmium chromium and lead in drinking water by electrothermal atomic absorption spectrometry using permanent modifiers. No use of modifier, iridium, ruthenium, rhodium and zirconium (independently, 500 μg) were tested to each one analyte through the pyrolysis and atomization temperatures curves. As the matrix is very simple, did not had occurred problems with the background for all metals. The best results obtained for cadmium and chromium was with the use of rhodium permanent modifier. For lead and aluminum, the best choice was the use of zirconium. The selection for the modifier took into account the sensitivity, form of the absorption pulse and low atomization temperature (what contributes to elevate the useful life of the graphite tube). For aluminum using zirconium permanent, the best pyrolysis and atomization temperatures were respectively, of 1000 and 2500 °C with a characteristic mass (1% of absorbance, m_o) of 19 pg (recommended of 20 pg). For cadmium, with use of rhodium the best temperatures for the pyrolysis and atomization were respectively of 400 and 1100 °C, with a symmetrical peak and with a m_o of 1.0 pg (recommended of 1.0 pg). For chromium with rhodium permanent, the best temperatures for pyrolysis and atomization were respectively of 1000 and 2200 °C, with symmetrical peak and m_o of 5.3 pg (recommended of 5.5 pg). For lead with zirconium permanent, the best temperatures for pyrolysis and atomization were of 700 and 2400 °C, with symmetrical peak and with m_o of 30 pg (recommended of 20 pg). Water samples spiked with each one of the metals in four different levels inside of the acceptable values presented recoveries always close to 100%. The detection limits were of 0.1 μg l⁻¹ for cadmium; 0.2 μg l⁻¹ for chromium; 0.5 μg l⁻¹ for lead and 1.4 μg l⁻¹ for aluminum.     

Isomer-dependent catalytic pyrolysis mechanism of the lignin model compounds catechol,resorcinol and hydroquinone

The catalytic pyrolysis mechanism of the initial lignin depolymerization products will help us develop biomass valorization strategies. How does isomerism influence reactivity, product formation, selectivities, and side reactions? By using imaging photoelectron photoion coincidence (iPEPICO) spectroscopy with synchrotron radiation, we reveal initial, short-lived reactive intermediates driving benzenediol catalytic pyrolysis over H-ZSM-5 catalyst. The detailed reaction mechanism unveils new pathways leading to the most important products and intermediates. Thanks to the two vicinal hydroxyl groups, catechol (o-benzenediol) is readily dehydrated to form fulvenone, a reactive ketene intermediate, and exhibits the highest reactivity. Fulvenone is hydrogenated on the catalyst surface to phenol or is decarbonylated to produce cyclopentadiene. Hydroquinone (p-benzenediol) mostly dehydrogenates to produce p-benzoquinone. Resorcinol, m-benzenediol, is the most stable isomer, because dehydration and dehydrogenation both involve biradicals owing to the meta position of the hydroxyl groups and are unfavorable. The three isomers may also interconvert in a minor reaction channel, which yields small amounts of cyclopentadiene and phenol via dehydroxylation and decarbonylation. We propose a generalized reaction mechanism for benzenediols in lignin catalytic pyrolysis and provide detailed mechanistic insights on how isomerism influences conversion and product formation. The mechanism accounts for processes ranging from decomposition reactions to molecular growth by initial polycyclic aromatic hydrocarbon (PAH) formation steps to yield, e.g., naphthalene. The latter involves a Diels–Alder dimerization of cyclopentadiene, isomerization, and dehydrogenation.

Detection of reactive intermediates with synchrotron radiation and photoelectron photoion coincidence methods reveals new mechanistic insights into lignin catalytic pyrolysis. Here we focus on how the isomerism changes the conversion and product formation.     

Lasers used in analytical micropyrolysis

Laser micropyrolysis gas chromatography mass spectrometry (GC-MS) allows analytical pyrolysis to be conducted with micro-spatial resolution. Despite the large range of contemporary laser sources, most previous laser pyrolysis studies have been conducted with continuous wave (CW) infrared irradiation. Here, the laser micropyrolysis analysis of a Sydney torbanite was conducted with three different laser sources - 1. CW 532 nm; 2. Q-Switched (QSw) pulsed 1064 nm; and 3. QSw pulsed 266 nm - to compare the molecular analyses attributes of different laser types (λ: 266-1064 nm; CW or QSw). The CW 532 nm laser irradiation consistently produced high concentrations of n-hydrocarbons, with lesser amounts of cyclic and aromatic hydrocarbons, similar to previous analyses with both CW 1064 nm laser pyrolysis and conventional analytical pyrolysis [1]. In contrast, both the IR and UV QSw pulsed irradiation sources provided poor and varied data. Relatively low concentrations of n-hydrocarbons were occasionally produced, but most often no structurally significant products were detected. The poor maintenance of hydrocarbon structural units by the short pulse lasers can be attributed to the very high power density delivered, leading to excessive degradation of the irradiated macromolecule.