Thermal decomposition kinetics of some aromatic azomonoethers

Thermal analysis of 4-[(4-chlorobenzyl)oxy]-4′-chloro-azobenzene dye, exhibiting liquid crystalline properties, was performed in dynamic air atmosphere. The compound behavior was investigated using TG, DTG, DTA and DSC techniques, under non-isothermal linear regime. The evolved gases were analyzed by FTIR spectroscopy. Kinetic parameters of the first decomposition step were obtained by means of multi-heating rates methods, such as isoconversioanl methods, IKP method and Perez-Maqueda et al. criterion.     

A density functional theory study of the gas-phase elimination reactions of 4-arylideneimino-1,2,4-triazol-3(2H )-ones and their 3(2H )-thione analogues

Theoretical studies on the thermolysis in the gas phase of 4-arylideneimino-1,2,4-triazol-3(2H)-ones and 4-arylideneimino-1,2,4-triazol-3(2H)-thiones were carried out using density functional theory methods, at the B3LYP/6-31G(d) and B3LYP/6-311+G(2d,p) levels of theory. The proposed reaction mechanism occurs in one step, leading to the formation of 3-hydroxy-(2H)-1,2,4-triazole or 3-mercapto-(2H)-1,2,4-triazole and a 4-substituted benzonitrile, via a six-membered cyclic transition state. The progress of the reactions was followed by means of the Wiberg bond indices. The results indicate that the transition states have character intermediate between reactants and products, and the calculated synchronicities show that the reactions are slightly asynchronous, in the case of triazolones, and show a higher asynchronicity in the case of triazolthiones. The bond-breaking processes are slightly more advanced than the bond-forming ones, indicating a small bond deficiency in the transition states. Kinetic and activation parameters for the reactions studied have been calculated and compared with available experimental data.From the Proceedings of the 28th Congreso deQuímicos Teóricos de Expresión Latina (QUITEL 2002)     

Methylierung von 4-Hydroxy-4-(2-piperidyl)-4H-pyrazolo [1,5-a]indol mit Formaldehyd und Ameisensäure. 11. Mitteilung über metallorganische Reaktionen und Folgeprodukte

In the 10^th communication of this series [1] the synthesis of 4-hydroxy-4-(2-piperidyl)-4H-pyrazolo[1,5-a]indole ( 4 ) was described (Scheme). Surprisingly enough, methylation of this compound with formaldehyde and formic acid led via ring closure and a subsequent rearrangement to a pentacyclic ketone. By means of ¹³C-NMR.-spectroscopy and mass spectroscopy, this ketone could be identified as a indolizino-pyrazolo-indole ( 9 ). Its structure and configuration were determined by X-ray structure analysis.     

Dynamic and Isothermal Thermogravimetric Degradation of Poly(vinyl Chloride)/Chlorinated Poly(ethylene) Blends

The thermal degradation of poly(vinyl chloride)/chlorinated poly(ethylene) (PVC/CPE) blends of different compositions was investigated by means of dynamic and isothermal thermogravimetric analysis in flowing atmosphere of nitrogen. Kinetic parameters (the apparent activation energy E, and pre-exponential factor Z) were calculated after Flynn-Wall-Ozawa method for the first stage of dynamic degradation of PVC/CPE blends, and after Flynn method for the isothermal degradation. In both cases, there is the compensation dependence between the values E and logZ. The values of compensation ratios as well as the characteristics of TG and DTG curves, confirm the stabilizing effect of CPE on PVC dehydrochlorination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diarylheptanoids from the fresh pericarps of Juglans sigillata

One new diarylheptanoid (3S)-3′, 4″-epoxy-1-(4′-hydroxylphenyl)-7-(3″-hydroxylphenyl) heptane-3-hydroxy (1), together with eleven known ones (2–12), was isolated from the fresh pericarps of Juglans sigillata. Their structures were elucidated on the basis of extensive spectroscopic methods, including HR-ESI-MS, 1D and 2D-NMR. All isolates were evaluated for their cytotoxic activities in vitro against the growth of human cancer cells lines HT-29 and MCF-7 by MTT assay.     

Biocatalytic Deracemization of 1,4-Benzodiazepines in the Synthesis of Enantiomerically Pure Serine

An efficient stereocontrolled synthesis of (S)-N-Cbz-serine (Cbz = benzyloxycarbonyl; 12 ) and of its (R)-enantiomer is reported. Kinetic resolution of the easily available racemic 3-(hydroxymethyl)-1,4-benzodiazepin-2-ones is performed in the key step via acetylation by the immobilized Mucor miehei lipase (Lipozyme IM) at 60°. This method is characterized by high enantiomer purity (ee's ges; 99%) of the intermediary alcohols (+)- 8 and (+)- 9 and acetates (?)- 10 and (?)- 11 , as well as of the final products (S)- and (R)-N-Cbz-serine, simple recycling of the biocatalyst, complete recovery of 2-aminobenzophenones ( 3 and 4 ) and their recycling into production of 1,4-benzodiazepines, and possibility to selectively racemize ‘wrong’ enantiomers of the alcohols 8 and 9 in the presence of Amberlite CG 400.     

Synthesis of Aryl- and Pyridinyl-substituted 2-Amino-6-thioxopyridine-3-carbonitrile Derivatives by Tandem Michael Addition and Cyclization Reactions

Summary. The tandem Michael addition and cyclization of 2-, 3-, and (4-pyridinylcarbonyl) thioacetanilides with arylidenemalononitriles yielded polysubstituted pyridines and bipyridines. Tetrahydro-6-thioxopyridine-3-carbonitrile was dehydrogenated to its dihydro derivative by means of HgO or DBU. The reaction of enamines of 3-, and (4-pyridinylcarbonyl)thioacetanilides with malononitrile furnished 3,4′- and 4,4′-bipyridines.     

Kinetic Resolution of 2-Chloro-1-（3,4-dichlorophenyl）ethanol by Lipase-Catalyzed Transesterification

Kinetic resolution of racemic 2-chloro-1-（3,4-dichlorophenyl）ethanol was performed by free Alcaligene sp. lipase-catalyzed irreversible transesterification affording the （R）-isomer with ≥95% ee and the （S）-isomer with ≥90% ee. The activity of lipase Alcaligene sp. strongly depends on the basicity of the reaction system, and an organic base such as triethylamine can enhance the activity of the lipase and enantioselectivity markedly.     

Kinetic models for solution imidization of polyamic acid containing naphthalene‐pendant group

The kinetics and mechanisms of the solution imidization of polyamic acid resulting from a diamine, bis(4‐aminophenoxy‐3,5‐dimethylphenyl)naphthylmethane, and a dianhydride, 3,3′4,4′‐diphenylsulfonetetracarboxylic dianhydride, were studied at three various temperatures (145, 165, and 180 °C). The results were confirmed by means of ¹H NMR and gel permeation chromatography (GPC). Kinetic parameters were obtained by an isothermal study, and the results were quite close to second‐order kinetics for the homogeneous solution imidization. In addition, Carother's equation, Mark–Houwink theory, and GPC were used to explain the molecular weight of the imidization processes. The apparent activation energy (E_a) was 104 KJ/mol, and the pre‐exponential factor (k₀) was 3.48 × 10¹⁴. The proposed kinetic mechanism is in good agreement with the kinetic models. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4139–4151, 2001     

Beitrag zum Reaktionsmechanismus der Synthese von Seychellen [1]

New Mechanistical Details Concerning the Synthesis of Seychellen [1] In the last step of our synthesis of Seychellen ( 2 ) [1], the solvolysis of 1 , only one side-product was formed, namely 3 (Scheme 1). Now the structure of 3 has been elucidated, mainly by spectroscopic studies of its derivatives 7 and 9 (Scheme 2). In order to differentiate between two different solvolytic pathways from 1 to 3 (see Scheme 1 and 3) d₃- 1 was prepared. Solvolysis of d₃- 1 proved the mechanism shown in Scheme 1. Solvolysis of 1 and of 2-epi- 1 , respectively, furnished the same product distribution, which makes a common intermediate a very probable. In both cases 10 is an intermediate, which is slowly converted into 2 and 3 . 2-epi- 1 was prepared from 1 (Scheme 5). Kinetic measurements with 1 , d₃- 1 and 2-epi- 1 are also in agreement with the mechanism drawn in Scheme 4: k₁(72°) = (5,2±0,5) · 10^?5 sec^?1, k₁(H)/k₁(D)(72°) = 1,4±0,15; k₂(H)/k₄(H) = 0,66 and k₂(H)/k₂(D) = 2,2 if k₄(H) ≈ k₄(D) is assumed.     

Study of mechanism and kinetic modeling of CO hydrogenation reaction over the impregnated Co-Ni/Al2O3 catalyst

An investigation of the kinetic and mechanism of CO hydrogenation reaction was performed on impregnated Co-Ni/Al₂O₃. Determination of kinetic parameters from the experiments was carried out in a micro fixed-bed reactor. Kinetic evaluations were performed under various operational conditions of T = 473–673 K, p = 1–14 bar, H₂/CO = 1–3, and GHSV = 4,500 hr⁻¹. Kinetic models and rate equations for CO consumption were obtained by using two main-type rate equations of Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER). Estimation of various kinetic parameters was performed using a nonlinear regression method. According to the obtained experimental results and using statistical criteria, one kinetic expression based on the LHHW mechanism (-r_CO = k_p.b_CO.P_CO. b_H2. P_H2/[1+ b_CO.P_CO + b_H2.P_H2]²) was chosen as the best-fitted model. For this fitted model, the activation energy was found to be 109.2 kJ/mol. Characterization of the catalyst was also performed using X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), and energy-dispersive x-ray spectrometer (EDS) techniques.     

A new isoflavanone from the trunk of Horsfieldia pandurifolia

A new isoflavanone, 2,2′-epoxy-4′-methoxy-3,7-dihydroxyisoflavanone (1), and a new natural coumaranone, 2-hyroxy-2-(4′-methoxybenzyl)-6-methoxy-3-coumaranone (2), along with 26 known compounds, were first isolated from the trunk of Horsfieldia pandurifolia. Their structures were elucidated by the means of spectroscopic analysis. Compound 1 was assessed for its cytotoxicity against five human tumour lines (HL-60, SMMC-7721, A-549, MCF-7 and SW-480), and the result showed that it has no activity.     

A kinetic study on the thermal behaviour of chitosan

The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal conditions, at several heating rates, between 5 and 30°C min⁻¹. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained by applying different conventional calculating methods is also shown.     

Thermal reaction of HNCO with NO2 at moderate temperatures

The thermal reaction of HNCO with NO₂ has been studied in the temperature range of 623 to 773 K by FTIR spectrometry. Major products measured are CO₂ and NO with a small amount of N₂O. Kinetic modeling of the time resolved concentration profiles of the reactants and products, aided by the thermochemical data of various likely reactive intermediates computed by means of the BAC-MP4 method, allows us to conclude that the reaction is initiated exclusively by a new bimolecular process: with a rate constant, k₁ = 2.5 × 10¹²e^?13,100/T cm³/mols. The well-known bimolecular reaction is the only strong competitive process in this important reactive system throughout the temperature range studied. Kinetic modeling of NO formation and NO₂ decay rates gave rise to values of k₁₀ which were in close agreement with literature data. © 1993 John Wiley & Sons, Inc.     

Anticyanobacterial phenolic constituents from the aerial parts of Eupatorium fortunei Turcz

Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei. The new structures were elucidated to be 7,8,9-trihydroxythymol (1), and 8,10-didehydro-7,9-dihydroxythymol (2) by means of MS and NMR analysis. The known compounds were identified as 8,9,10-trihydroxythymol (3), 10-acetoxy-8,9-dihydroxythymol (4), o-coumaric acid (5) and 4-(2-hydroxyethyl)benzaldehyde (6). Compound 3 showed strongest inhibitory effect on the growth of Microcystis aeruginosa in comparison with CuSO₄.     

Deuterium labelled liquid crystalline compounds

Abstract

The synthesis of 4-(2′-methylbutyl)phenyl4′n-heptylbiphenyl-4-carboxylate-d ₁₈(7BEF5-d ₁₈) is presented. The compound is intended to be used as a means of studying the collective modes of liquid crystals by the coherent inelastic neutron scattering technique. The 4′-n-heptylbiphenyl-4-carboxylic acid-d ₁₂, a liquid crystalline intermediate was prepared as well; its acid chloride was coupled with 4-(2′-methylbutyl)phenol-d ₆ to obtain the final product. The intermediates and final products were investigated by spectroscopic methods.     

Preparation of (Pentafluorosulfanyl)benzenes by Direct Fluorination of Diaryldisulfides: Synthetic Approach and Mechanistic Aspects

Direct fluorination of ortho-, meta- and para-substituted aromatic thiols and disulfides using elemental fluorine afforded substituted (pentafluorosulfanyl)benzenes. This work thus represents the first study of the scope and limitation of direct fluorination for the synthesis of new SF₅-containing building blocks. Fluorinations in batch and flow modes were compared. A comprehensive computational study was carried out employing density functional and wave function methods to elucidate the reaction mechanism of the transformation of ArSF₃ into ArSF₅. Eliminating various nonradical pathways, it has been shown that the reaction proceeds by a radical mechanism, initiated by the attack of the F^. on the ArSF₃ moiety, propagated via an almost barrierless F₂+ArSF₄^.→ArSF₅+F^. step and terminated by the ArSF₄^.+F^.→ArSF₅. Most of the calculated data are in very good agreement with experimental observations concerning the ortho-substituent effect on the reaction rates and yields.     

Thioether glycidyl resins. VI. Reaction products of opening of oxirane ring of phenylthioetherglycidyl resin and of some derivatives under the influence of temperature

The process of oxirane ring opening of thioether glycidyl resins under various temperatures has been described. Reaction rate constants (k) and the activaton parameters (E_α, ΔH*, ΔS*) for epoxy group loss of 1,2-epoxy-3-(phenylthio)propane, 1,2-epoxy-3-(p-tolythio)propane, and 1,2-epoxy-3-(p-chloro-phenylthio)propane using classical kinetic methods were determined. The reaction products were separated and analyzed by means of chromatography and the structure of the compounds was determined by means of the spectral analyses: IR, ¹H-NMR, and ¹³C-NMR     

The Intermetallic Type-I Clathrate Na8Zn4Ge42

The new intermetallic type-I clathrate Na₈Zn₄Ge₄₂ was obtained by direct reaction of the elements, and its crystal structure was determined by means of single-crystal X-ray diffraction methods. The structure is described in space group Pm3 n (no. 223) with a = 10.6982(1) Å. A mixed Zn/Ge occupancy is found for one of the network sites (6c). Na₈Zn₄Ge₄₂ represents an air-stable electron-precise Zintl phase with exclusively Na cations located in the cavities of a polyanionic host network of four-connected Zn and Ge atoms.     

Characterization of Autocatalytic Reactions in Modified Cellulose/NMMO Solutions by Thermal Analysis and UV/VIS Spectroscopy

The thermal stability of cellulose/N-methylmorpholine-N-oxide (NMMO) solutions were investigated using UV/VIS spectrometry with a temperature programming cuvette and caloric measurements by means of the Systag calorimeter RADEX (mini-autoclave). Both analytical methods allow to characterize the influences of stabilizers and additives. With the temporal course of the optical density, temperature and pressure thermal runaway reactions with gas evolution and accumulation of chromophoric degradation products were recognized. Kinetic model calculations compared with UV/VIS measurements demonstrate the existence of autocatalytic reactions in cellulose/NMMO solutions. Varying the heating rate autocatalysis can be proved by dynamic caloric measurements as well.