Thermal degradation of polyurethanes. Model compounds

An analysis was carried out of degradation products of model compounds polyethylene glycol and ethylene diphenylcarbamate. Pyrolysis has been effected at 350 and 400°C under nitrogen and in vacuo. The products were analyzed by gas chromatography. Aniline, CO₂, CO, C₂H₄, CH₃CHO, etc., were found.     

Influence of Aluminium Alkyl Compounds on the High‐Pressure Polymerization of Ethylene with Ternary Metallocene‐Based Catalysts. Investigation of Chain Transfer to the Aluminium

The influence of aluminium alkyl compounds on metallocene‐catalyzed high pressure polymerizations of ethylene has been investigated at 150 MPa and 180°C in a continuously operated autoclave. The catalysts were based on the metallocenes bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂) and diphenylmethylene (cyclopentadienylfluorenyl)zirconium dichloride (Ph₂C‐(CpFlu)ZrCl₂), which were preactivated outside the reactor with triisobutylaluminium (TiBA) and N,N‐dimethylanilinium tetrakis(pentafluorophenyl)borate (DMAP, [PhNHMe₂][B(C₆F₅)₄]). The concentrations of triisobutylaluminium (TiBA) and triethylaluminium (TEA) in the reactor were varied over a wide range, using a separate dosing for these two aluminium alkyl compounds. Productivity and polymer properties strongly depended on the type and the concentration of the aluminium alkyl compound used. Highest productivities and molecular weights were obtained with low concentrations of TiBA in the reactor. Up to a concentration of 30 molppm Al in the reactor, unimodal polymers were formed with M̄_w/M̄_n between 2 and 3. With higher aluminium concentrations the products formed contained small amounts of waxes, due to oligomerization catalyzed by the aluminium alkyl compounds. The molecular weight distributions (MWDs) of these products could be described as a superimposition of two Schulz‐Zimm distributions. All MWDs were analyzed with regard to the amount of waxes produced by ethylene oligomerization and with regard to the influence of chain transfer reactions to the aluminium. The rate constants of chain transfer to aluminium, in relation to the rate constants of insertion of ethylene, were estimated.     

Estimating Heats of Detonation and Detonation Velocities of Aromatic Energetic Compounds

A new method is introduced to predict reliable estimation of heats of detonation of aromatic energetic compounds. At first step, this procedure assumes that the heat of detonation of an explosive compound of composition C_aH_bN_cO_d can be approximated as the difference between the heat of formation of all H₂O CO₂ arbitrary (H₂O, CO₂, N₂) detonation products and that of the explosive, divided by the formula weight of the explosive. Overestimated results based on (H₂O CO₂ arbitrary) can be corrected in the next step. Predicted heats of detonation of pure energetic compounds with the product H₂O in the liquid state for 31 aromatic energetic compounds have a root mean square (rms) deviation of 2.08 and 0.34 kJ g⁻¹ from experiment for (H₂O CO₂ arbitrary) and new method, respectively. The new method also gives good results as compared to the second sets of decomposition products, which consider H₂, N₂, H₂O, CO, and CO₂ as major gaseous products. It is shown here how the predicted heats of detonation by the new method can be used to obtain reliable estimation of detonation velocity over a wide range of loading densities.     

The mechanism of stabilization of poly(vinyl chloride). II. Cleavage of organotin sulfur compounds by anhydrous hydrogen chloride

A number of organotin compounds of the type R_nSn Y_4–n, where R = alkyl or aryl; Y = alkylthio, arylthio or carbothiolate; and n = 1, 2, 3 have been prepared and treated with hydrogen chloride at 180°C in o-dichlorobenzene solution. The organotin compounds were also tested at 190°C as thermal stabilizers for PVC. Cleavage of tin–carbon bonds by hydrogen chloride was demonstrated in some cases by analysis of the organotin–hydrogen chloride reaction products. The formation of monoalkyl(aryl)tin chlorides or stannic chloride, or both, in the model system was shown to correspond to a catastrophic mode of degradation in the polymer. The use of stabilizers with fewer than two alkyl or aryl groups on tin also gave this mode of degradation.     

Synergism on antioxidant activity between natural compounds optimized by response surface methodology

Despite the increase in the use of natural compounds in place of synthetic derivatives as antioxidants in food products, the extent of this substitution is limited by cost constraints. Thus, the objective of this study was to explore the synergism on the antioxidant activity of natural compounds, for further application in food products. Three hydrosoluble compounds (x₁ = caffeic acid, x₂ = carnosic acid, and x₃ = glutathione) and three liposoluble compounds (x₁ = quercetin, x₂ = rutin, and x₃ = genistein) were mixed according to a “centroid simplex design”. The antioxidant activity of the mixtures was analyzed by the ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) methodologies, and activity was also evaluated in an oxidized mixed micelle prepared with linoleic acid (LAOX). Cubic polynomial models with predictive capacity were obtained when the mixtures were submitted to the LAOX methodology (? = 0.56 x₁ + 0.59 x₂ + 0.04 x₃ + 0.41 x₁x₂ – 0.41 x₁x₃ – 1.12 x₂x₃ – 4.01 x₁x₂x₃) for the hydrosoluble compounds, and to FRAP methodology (? = 3.26 x₁ + 2.39 x₂ + 0.04 x₃ + 1.51 x₁x₂ + 1.03 x₁x₃ + 0.29 x₂x₃ + 3.20 x₁x₂x₃) for the liposoluble compounds. Optimization of the models suggested that a mixture containing 47% caffeic acid + 53% carnosic acid and a mixture containing 67% quercetin + 33% rutin were potential synergistic combinations for further evaluation using a food matrix.     

Influence of organophosphorus inhibitors on the structure of atmospheric lean and rich methane-oxygen flames

The inhibition of atmospheric laminar methane-oxygen flames of various compositions by trimethyl phosphate was studied experimentally and by numerical modeling using mechanisms based on detailed kinetics. The H and OH concentration profiles in flames with and without the addition of trimethyl phosphate were measured and calculated. It was shown that the addition of the inhibitor reduced the maximum (in the reaction zone) concentrations of H and OH in lean and rich flames. The concentration reduction was higher in rich flames than in lean flames. The concentration profiles of the phosphorus-containing products PO, PO₂, HOPO, HOPO₂, and (HO)₃PO in lean and rich flames stabilized on a flat burner were measured and calculated. Tests of the previously developed model of flame inhibition by phosphorus compounds showed that the model provides adequate predictions of many experimental results. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 23–31, March–April, 2007.     

Synergistic Effects in the Extraction of Uranium(VI) by Di-4-octylphenyl Phosphoric Acid

Abstract

The extraction of uranium(VI) from sulfuric acid solutions by di-4-octylphenyl phosphoric acid (DOPPA) is enhanced by the addition of neutral organophosphorus compounds due to synergistic action. The effect of tri-n-butyl phosphate (TBP), dibutylbutyl phosphonate (DBBP), and tri-n-octyl phosphine oxide (TOPO) was studied. The synergistic effect increased in this order. In the case of TBP and DBBP the extraction coefficient for U(VI) decreased with increasing concentration of synergistic agent after reaching a maximum. With TOPO, on the other hand, there was an increase even after this limit. This was because of the extraction of uranium by TOPO itself. The effect of uranium loading in the organic phase on the synergistic behavior was studied and the results were compared with those obtained with di-2-ethylhexyl phosphoric acid (DEHPA) in the presence of the same synergistic agents. The results with these two extractants indicate that with TOPO the synergism is mainly due to the formation of substitution products of the type UO₂A₂B₂ and with TBP addition products of the type UO₂(HA₂)₂B.     

Synthesis and properties of TLCPs with 2,6‐naphthalene‐based mesogen,polymethylene spacer,and nonlinear 4,4′‐thiodiphenyl links

A series of new thermotropic main‐chain liquid crystalline copolyesters were prepared by polycondensation of 2,6‐naphthalenedicarbonyl chloride, 4,4′‐thiodiphenol, and α,ω‐alkanediols (n = 4–10) in diphenyl ether at 200°C. Thermal transition behaviors of these copolyesters were investigated by differential scanning calorimetry. Moreover, their thermal stabilities and mesomorphic textures were studied by thermogravimetric analysis and polarizing optical microscopy, respectively. Corresponding model compounds with terminal mesogenic units and central polymethylene spacers were also synthesized for comparison. Both copolymers and model compounds exhibit odd–even dependency of melting temperatures, transition enthalpy (ΔH_m), and entropy (ΔS_m) on the number of methylene units in the spacer. However, the odd–even effects in model compounds are much more distinctive. Nematic mesophases are the only texture observed in melts, except the model compounds with longer methylene units (n = 8, 10), in which smectic mesophases can be observed. The T_m values of the copolyesters (TDP/HD = 1/1) are between 233 and 259°C, depending on spacer length. The initial decomposition temperatures of the copolyesters are above 419°C under N₂ atmosphere. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1536–1546, 2002     

Photochemical Degradation of 1- and 2-methylphenanthrenes in Acetonitrile and on Some Solids

In order to obtain basic information about photochemical degradability and degradation products for 1- and 2-methylphenanthrenes (MPs), photodegradation of these compounds in an organic solvent (acetonitrile) and on some solids (soil, silica gel [SiO₂], and titanium dioxide [TiO₂]) were carried out in a laboratory using solar simulators.

The results showed that the degradation rate (%) increases in the order of TiO₂ > SiO₂ > acetonitrile > soil. Products formed in acetonitrile included aromatic compounds with molecular ion [M⁺] peaks at m/z = 148, 162, 198, 206, 208, 210, 222, 224 and 238. In case of 1 MP, a compound with M⁺ 206, which was identified as 1-phenanthrene-carbaldehyde, was predominantly formed. However, 2MP showed no predominance for M⁺ 206 and also yielded M⁺ 210 and M⁺ 224 as major products. Degradation on soil and SiO₂ gave similar products to those detected in acetonitrile, while that on TiO₂ gave different products from the formers. Based on the results of product analysis, three degradation pathways which may occur in acetonitrile are proposed.     

Analysis of thermal degradation for plastic optical fibers

Attenuation loss of plastic optical fibers (POFs) gradually increases with long use at high temperatures. We separated attenuation loss of the POFs before and after heating at 150°C in air into four loss factors, and identified the main factor for attenuation loss increase as electronic transition absorption loss (α_e). The increase of α_e was caused by a thermal oxidation reaction of the core polymer in the POF. But, according to NMR and FT-IR spectra, elementary analysis, etc., hardly any reaction products were detected. We assume that the reaction products were only a small amount of the conjugated carbonyl groups. So we fabricated POFs containing model compounds with conjugated carbonyl groups, and measured their attenuation loss. The attenuation loss spectra of these POFs were similar to those of thermally degraded POFs. Consequently, a very small amount of conjugated carbonyl groups were formed by the thermal oxidation reaction of core polymer so that α_e increased to an unacceptable level.     

Microwave Discharge of O2 and CO2 as a Synthetic Tool for Oxidations of Unsaturated Compounds Adsorbed on Solid Supports

Cis and trans stilbene, styrene, 1-decene and 6-dodecene adsorbed on silica gel were reacted with oxygen atoms produced by microwave discharge of O₂ and CO₂. At 0°C these compounds gave mainly epoxides and carbonyl compounds as in neat liquid reactions. Below — 60°C ozonolysis products were formed; cis and trans stilbene and styrene gave benzaldehyde while 1-decene and 6-dodecene resulted mainly in ozonides.     

Ozonation,Ozone/UV and UV/H2O2 Degradation of Chlorophenols

The performance of the O₃, O₃/UV and UV/H₂O₂ processes for degradation of six chlorophenols (4-chlorophenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) were studied in laboratory reactors. Comparative study showed that chlorophenols can be degraded successfully by all of the methods studied, whilst traditional ozonation at high pH was determined to be the most effective method to treat chlorophenols. Even though the molar absorptivity of chlorophenols is known to be relatively high in the UV-region, the combination of UV-radiation with ozone did not accelerate the degradation of chlorophenols further. The toxicity of degradation products formed during ozonation of chlorophenols has been compared with the toxicity of pure chlorophenols utilizing Daphnia magna 24 hours test. Ozonation of chlorophenols yielded less toxic or even nontoxic products for Daphnia magna compared with parent compounds.     

Synthesis of series of pure polyethylene glycol ethers based onn-tridecanol,7-tridecanol,and oxo-process tridecyl alcohol

Puren-tridecyl, 7-tridecyl andoxo-tridecyl polyethylene glycol monoethers, C₁₃H₂₇O (C₂H₄O)_nH, were made by the Williamson reaction with n=4,6,8,10 and 12. Related crystalline diethers derived fromn-tridecanol were made in the range of 4–16 oxyethylene units. The compounds were extensively purified by crystallization (where applicable) or by chromatography and distillation. The final products are new compounds important for comparative studies of surface properties. Characterizing constants and physical properties including those of a large number of pure intermediates are reported. All but the lowest member of then-tridecyl monoether series are crystalline, melting between 26 and 40C. The related diethers melting between 37 and 50C have a minimum melting point when they contain between 6 and 8 oxyethylene units. Theoxo-tridecyl and 7-tridecyl monoethers are liquids.     

Structural and Activity Investigation into Al<Superscript>3+</Superscript>, La<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

Abstract  

Twelve phosphomolybdate compounds were synthesized via cationic exchange and were of the form: M _x H_3–3x [PMo₁₂O₄₀] (M = Al, La or Ce; 0 ≤ x ≤ 1). These compounds were analyzed by XRD and adsorption isotherm. Aluminum addition causes a primitive cubic phase, while lanthanum and cerium yield body-centered structures. La and Ce addition reduces surface area of phosphomolybdate structure. Temperature-programmed experiments for the selective oxidation of isobutane yielded methacrolein, 3-methyl-2-oxetanone (lactone), acetic acid (not with aluminous compounds), propene (only with aluminous compounds), carbon dioxide and water. The preference for propene rather than acetic acid formation with Al³⁺ may be due to the smaller cation size, or primitive cubic structure. These products form via two distinct reaction processes, labeled categories 1 and 2. Category 1 formation is associated with isobutane forming products on the surface, but reaction rate determined by bulk migration of charged particles. Category 2 formation is concerned with isobutane penetrating deep within the bulk of the substrate and forming products which subsequently desorb in a series of bell-shaped humps. Methacrolein forms via both category 1 and 2, whilst all other products form via category 2 exclusively. Kinetic analysis showed apparent activation barriers for category 1 methacrolein formation range from 67 ± 2 kJ mol⁻¹ to >350 kJ mol⁻¹, and occur in groups with small, medium and large activation barriers. The addition of +3 metal cations to the phosphomolybdate anion increase thermal stability, significantly decreasing deactivation; IR spectroscopy shows that the Keggin structure remains intact during temperature-programmed experiments with the Al, La and Ce salts.     

Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

Abstract  

Various phosphomolybdates were synthesized using cations from Groups 1 and 2 of the periodic table. These compounds were of the form M _x H_3−xn [PMo₁₂O₄₀], with n being the cationic charge (+1 or +2). XRD analysis shows pure phosphomolybdic acid has a triclinic structure. A body centered cubic (BCC) structure gradually develops with addition of Group 1 cations, and the triclinic phase is completely replaced by the BCC phase once metal cations occupy a volume greater than 9–11 ?³ per phosphomolybdate anion. The Group 2 compounds do not form a cubic phase, however the triclinic phase distorts once cationic volume is greater about 5 or 6 ?³ and appears to become somewhat amorphous. Isobutane selective oxidation over the compounds yielded methacrolein (primary product), 3-methyl-2-oxetanone (lactone), acetic acid, propene, methacrylic acid, carbon dioxide and water as products. Propene was formed over the Group 1 compounds exclusively and methacrylic acid formation was observed with BaH[PMo₁₂O₄₀] only. Products form via two distinct processes: Category 1 product has an exponential profile and coverage is consistent with a Langmuir model, Category 2 formations are consistent with desorptions from within the bulk of the substrates. Methacrolein forms via both Category 1 and 2 processes, whilst all other products are formed by Category 2 exclusively. A rigorous kinetic analysis yielded accurate activation parameters. Category 1 methacrolein formation apparent activation energies ranged from 34.7 ± 1.3 to 119 ± 4 kJ mol⁻¹. Category 2 formations ranged from 34.3 ± 0.4 to 726 ± 172 kJ mol⁻¹. No relationship between activity and composition or structure could be ascertained, despite investigation into correlations using several different models.     

Structure‐Based Virtual Screening for Dopamine D2 Receptor Ligands as Potential Antipsychotics

Structure‐based virtual screening using a D₂ receptor homology model was performed to identify dopamine D₂ receptor ligands as potential antipsychotics. From screening a library of 6.5 million compounds, 21 were selected and were subjected to experimental validation. From these 21 compounds tested, ten D₂ ligands were identified (47.6 % success rate, among them D₂ receptor antagonists, as expected) that have additional affinity for other receptors tested, in particular 5‐HT_2A receptors. The affinity (K_i values) of the compounds ranged from 58 nm to about 24 μm . Similarity and fragment analysis indicated a significant degree of structural novelty among the identified compounds. We found one D₂ receptor antagonist that did not have a protonatable nitrogen atom, which is a key structural element of the classical D₂ pharmacophore model necessary for interaction with the conserved Asp(3.32) residue. This compound exhibited greater than 20‐fold binding selectivity for the D₂ receptor over the D₃ receptor. We provide additional evidence that the amide hydrogen atom of this compound forms a hydrogen bond with Asp(3.32), as determined by tests of its derivatives that cannot maintain this interaction.     

Action des trihalogenures de chrome sur le graphite: Synthese et etude des composes graphite-chlorure chromique

As indicated by Croft[1], then Leparlier[2] the insertion of chromium trichloride can be carried out with difficulty leading in all cases to inhomogeneous products. Chromium tribromide[3] and chromium tri-iodide[4] cannot be intercalated.Figure 1 shows the quantity of chromium trichloride fixed by natural graphite (250 < θ < 500μ) as a function of the temperature for one week of reaction. The insertion whose effect is to dislocate the large diameter crystallites (Fig. 2) only takes place on the periphery of the pyrographite samples (Fig. 3). Heated in vacuum, the graphite-CrCl₃ products dissociate only at relatively high temperatures (Fig. 4). Study of the X-ray data presented in Table 1 indicates that the products of formulae comprised between C₂₂CrCl₃ and C₂₉CrCl₃ are third stage compounds ( ). The quantity of free graphite increases as that of the inserted halogenide decreases (Fig. 6). The product of average composition C₂₁CrCl₃ obtained on large crystallites (1 < θ < 2 mm) is in reality a mixture of both second and third stages, although the X-ray diagram carried out on the fine portion obtained by dislocations of the large grains reveals only a second stage of c-axis periodicity . Contrary to the graphite-FeCl₃ compounds[13,14], the powdered graphite-CrCl₃ products could not be prepared in pure stage states[15].Both X-ray diffraction (Fig. 7) and electron microdiffraction (Fig. 8) data show that the chromium trichloride layers conserve their own structure. The two hexagonal sublattices, one corresponding to the graphite ( ), the other to the intercalated trichloride ( ) are turned by an angle of 30° as in the case of graphite-FeCl₃ compounds[12],Studies carried out on single crystals allowed us to determine the relative disposition along the c-axis of the carbon layers A and the halogenide layers α. In the first stage graphite-FeCl₃ products, the photographs (Fig. 9) lead unambiguously to the sequence AαAα…In the third stage graphite-CrCl₃ compounds (Fig. 10) analysis of the rotating crystal photographs do not allow us to choose between the two sequences AαABAαA and AαAAAαA…Thermomagnetic curves of the rich products (Fig. 11) show that the magnetic behaviour of the intercalated chromium chloride is close to that of the free chloride: the extrapolated Curie-Weiss temperature (27 ± 3°K) is in the neighbourhood of that the halogenide (32°K); the magnetic moment of the chrome ion (3.60 μ_B) is very similar to that of Cr³⁺ ions (3.85 μ_B) measured on CrCl₃.     

Synthesis of switchable amphipathic molecules triggered by CO2 through carbonyl‐amine condensation

Five long‐chain alkyl amidines were synthesized by condensation of N,N‐dimethylacetamide with octylamine, decylamine, dodecylamine, tetradecylamine, and hexadecylamine, respectively. Synthesis conditions including solvent, pH, temperature, and ratio of reactants were studied. The series of long‐chain alkyl amidine compounds reacted with dry ice to produce amidinium bicarbonates cationic amphipathic molecules. The critical micelle concentration (cmc) and surface tension at cmc (γ_cmc) measured by drop volume method show that these amphipathic molecules have excellent surface activity. The changes of cationic content measured by two‐phase titration and conductivity before and after bubbling CO₂, show different properties between amidines and amidinium bicarbonates cationic amphipathic molecules. The switchable function of the amidinium bicarbonate cationic amphipathic molecule in emulsification and demulsification was studied. Practical applications : Our innovative work is synthesizing switchable amphipathic molecules, N′‐alkyl‐N,N‐dimethylacetamidines, by carbonyl‐amine condensation. Compared with a former way of synthesis, our work shows great potential advantages in industrial application. Our synthesis route is simpler with higher yield and is carried out at ambient temperature. Moreover, the products are environmentally friendly. Compared with traditional amphipathic molecules, our products, N′‐alkyl‐N,N‐dimethylacetamidines, show good switchable properties, which can be switched on and off, trigged by CO₂.This means these products can be reused for several times, which is significant for environmental protection.     

2-Ethylhexanol Derivatives as Nonionic Surfactants: Synthesis and Properties

The synthesis and basic properties of 2‐ethylhexanol based innovative nonionic surfactants are described in this paper. 2‐Ethylhexanol as an available and relatively inexpensive raw material was used as the hydrophobe source modified by propoxylation and followed by polyethoxylation. As the result, six series of 2‐ethylhexyl alcohol polyalkoxylates (EHP_mE_n) were obtained with three steps of propoxylation, each followed by polyethoxylation and two series only with polyethoxylation (EHE_n). Two different catalysts were used, a dimetalcyanide and KOH. Values of average conversion rates and chemical content of the obtained products (GC, TG and GPC techniques) were compared. The influence of the applied catalyst and polyaddition degree on the homologue distribution, reactant conversion and amount of byproducts is discussed. The basic physicochemical parameters including refractive index, solubility in polar media, foaming properties and wettability were investigated and compared. Furthermore, surface activity parameters, i.e. surface tension (γ_CMC) and critical micelle concentrations were determined. Results are compared to C_12–14 alcohol ethoxylates (LaE_n). Accordingly, it was found that the studied 2‐ethylhexyl alcohol based compounds are effective, low foaming nonionic surfactants.     

Transfer hydrogenation and transfer hydrogenolysis: XII. Selective hydrogenation of fatty acid methyl esters by various hydrogen donors

The selective hydrogenation of methyl linoleate was studied using various organic compounds as hydrogen sources in the presence of homogeneous and metallic palladium catalysts. Complete selectivity to monoenes and relatively little formation of isolatedtrans double bonds were realized by the hydrogen transfer from L-ascorbic acid at 47% conversion of starting material to hydrogenation products. The hydrogenation bytrans-1,2-cyclohexanediol catalyzed by RuH₂(PPh₃)₄ also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH₂(PPh₃)₄, also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH₂(PPh₃)₄, the presence of these hydroxy compounds increased the isomerization of methyl elaidate tocis-monoenes.