The Boudouard–Bell reaction analysis under high pressure conditions

A new method for the measurement of solid fuel reactivity towards carbon dioxide has been developed. This new method takes into account high-pressure and temperature effects. Three devolatilized carbonaceous materials have been used in experiments: chars derived from lignite, bituminous coal and blast furnace coke. Processes were carried out at temperatures of 800, 850 and 900?°C and pressures of 1.52, 2.5 and 3.4?MPa. Analysis of the product gas composition was carried out with the maximum degree of conversion of CO₂ (??_m) proposed as a representative reactivity parameter. Arrhenius and Eyring relationships have been analyzed, and values of the activation energy and activation volume have been calculated.     

The synthesis of ZnP4 based on liquid–solid reaction under high pressure and temperature

In this article we reported the successful high pressure and temperature synthesis of micron-sized zinc tetraphosphide (ZnP₄) crystals based on the liquid–solid reaction between Zn and P at a large-volume cubic press. Techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDXA) were employed to investigate the phase structure, grain size, morphology and stoichiometric ratio of crystals. The results indicate that the synthesized ZnP₄ has a tetragonal structure with the space group of P41212, and the grains with size of about 50 μm can be prepared at 4.0 GPa and 1000 °C. We also obtained the pressure–temperature (P–T) formation region of ZnP₄ and discussed the formative mechanism of ZnP₄ crystals.     

Oxidations of some α-amino acids under mitsunobu reaction conditions

Reactions of α-amino acids with azodicarboxylates and Ph₃P results in oxidation at the α-carbon. N-acyl or carbamoyl amino acid esters give azodicarobxylate adducts, whereas free α-amino acid esters are converted to the corresponding α-keto esters.     

Unexpected formation of β, meso-directly linked diporphyrins under Adler–Longo reaction conditions

Unexpected formation of β, meso-directly linked diporphyrin products has been described in the reactions of β-formyl porphyrins with pyrrole under Adler–Longo reaction conditions. Preliminary mechanistic studies indicates that β-dipyrromethane substituted porphyrin structure is the crucial intermediate for the formation of diporphyrin product.     

X-ray structure of palladium (II) complex and its catalytic activity on Suzuki–Miyaura reaction under mild conditions

Research on Chemical Intermediates - Palladium (II) complex with 4-tert-butylbenzoic hydrazide (TBBH)/triphenylphosphine (PPh3) ligands was successfully synthesized and characterized by X-ray,...     

β-Oxo-sulfoxide rearrangements under sila-Pummerer reaction conditions

Under sila-Pummerer reaction conditions, the β-oxo-sulfoxide 1 gave rise to a new pentacyclic compound 5. The structure of 5 was deduced from spectral data and by X-ray analysis of the sulfoxide 6 which was formed by subsequent oxidation.     

Characterization of poly(ethylene glycol)-b-poly(ε-caprolactone) by liquid chromatography under critical conditions: Influence of catalysts and reaction conditions on product composition

Amphiphilic block copolymers were synthesised by ring opening polymerization of ε-caprolactone with polyethylene glycol monomethyl ether (PEG-MME) using different catalysts (boron trifluoride, sodium hydride, and tin octoate) in a one pot procedure. The products obtained were characterized with respect to their molar mass distribution and content of homopolymers using size exclusion chromatography (SEC), Liquid chromatography under critical conditions (LCCC) and MALDI-TOF-MS. The homopolymers of caprolactone could be separated from the block copolymer by LCCC on a reversed phase column in tetrahydrofurane-water mobile phases with evaporative light scattering detection (ELSD). Residual monomer could be determined under the same conditions using density detection, a separation of the copolymer from residual initiator could be achieved on a normal phase column in acetone-water mobile phases.     

Improved hydrogen oxidation reaction under alkaline conditions by Au–Pt alloy nanoparticles

This work demonstrates the outstanding performance of alloyed Au_1 Pt_1 nanoparticles on hydrogen oxidation reaction(HOR) in alkaline solution. Due to the weakened hydrogen binding energy caused by uniform incorporation of Au, the alloyed Au_1 Pt_1/C nanoparticles exhibit superior HOR activity than commercial Pt Ru/C. On the contrary, the catalytic performance of the phase-segregated Au_2 Pt_1/C and Au_1 Pt_1/C bimetallic nanoparticles in HOR is significantly worse. Moreover, Au_1 Pt_1/C shows a remarkable durability with activity dropping only 4% after 3000 CV cycles, while performance attenuation of commercial Pt Ru/C is high up to 15% under the same condition. Our results indicate that the alloyed Au_1 Pt_1/C is a promising candidate to substitute commercial Pt Ru/C for hydrogen oxidation reaction in alkaline electrolyte.     

Prediction of thermodynamic properties of some polymeric systems using an extended LJ potential-based equation of state up to high temperature–high pressure conditions

In this work, the extended Lennard-Jones potential-based equation of state (ELJ-based EoS) on which the effective near-neighbour pair interactions are LJ (12,6,3) type has been used to predict the specific volume and other thermodynamic properties of some semi-crystalline and liquid polymers and copolymers up to extremely high temperature–high pressure conditions. It seems that, at least in the dense regions, there are no upper- and lower-specific volume limitations in the applicability of the model for different polymeric systems. The parameters can be determined at any temperature for each compound using the temperature dependence of the parameters of ELJ-based EoS. The calculated parameters have been used to calculate the specific volume and other derived thermodynamic properties of different polymeric systems at any temperature and pressure. The ELJ-based EoS has been also compared with some previous studies.     

Microwave-assisted Cannizzaro reaction—Optimisation of reaction conditions

The microwave-assisted Cannizzaro reaction was studied in order to develop fully reproducible synthetic protocols for transformation of aldehydes to carboxylic acid and alcohols. Optimised were the following process parameters: power, temperature, and time. Aromatic, heteroaromatic and aliphatic aldehydes were used in the studies. It was found that furfural, thiophene-2-carbaldehyde, pyridinecarboxaldehyde and aromatic aldehydes react under mild conditions, while 1-methyl-pyrrole-2-carboxaldehyde derivatives and aliphatic aldehydes require more drastic reaction conditions and a longer exposure time to microwave radiation.     

Synthesis of N-(ω-trimethylsilylalkyl)purines under conditions of interfacial catalysis

A Method of synthesis of N-(-trimethylsilylalkyl)purines, by alkylation of potassium salts of purine bases by 3-chloropropyltrimethylsilane and chloromethyltrimethylsilanes under conditions of interfacial catalysis, has been developed. Hydroxylation of the N-allyl group by dimethylphenylsilane, which is an alternative pathway of synthesis of silicon-containing purine derivatives, has been accomplished for the first time in the purine series. The structure of the compounds obtained was established by methods of PMR and UV spectroscopy.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 654-658, May, 1995. Original article submitted October 25, 1994.     

Measurement of the rotational viscosity, γ1 of nematic liquid crystals under high pressure

Abstract

A method for the measurement of the rotational viscosity, γ₁ of nematic liquid crystals under high pressure is described. First measurements for the liquid crystals 4'-methoxybenzylidene-4-n-butylaniline, a broad range nematic mixture of substituted cyclohexyl-phenyls and a re-entrant nematic mixture are presented.     

Effect of reaction conditions on surface properties of TEOS–TBOT–PDMS hybrid materials

Hybrid materials based on tetraethoxysilane (TEOS), tetrabutyl orthotitanate (TBOT), and hydroxyl terminated polydimethyl siloxane (PDMS) have been prepared and characterized. The effects of HCl concentration and PDMS molecular weight (M_W) have been analysed. The physical and chemical characteristics have been discussed based on the results obtained from the characterization by Raman spectroscopy, nitrogen adsorption, mercury intrusion porosimetry and inverse gas chromatography (IGC). Specific surface areas (SSA) and pore volumes increase with HCl concentration and are independent on the PDMS Mw. SSA values as high as 300 m² g⁻¹ have been obtained for hybrid materials prepared with HCl:(TEOS + TBOT) concentration of 0.3 and PDMS Mw of 550 g mol⁻¹. These materials present the higher pore volumes and lower pore sizes. However, for HCl:(TEOS + TBOT) concentration of 0.5, only macroporous materials are obtained with SSA values as low as 2–4 m² g⁻¹, and pore sizes close to 10 μm. In general the presence of Ti on the SSA and porosities give a little decrease in such values. Surface energies are consistent with those of organic–inorganic materials. Dispersive surface energies are higher for the Si–Ti hybrid materials and, for all of them, they decrease with both HCl concentration and PDMS Mw. This result can be assigned to the presence of a higher concentration of PDMS (or CH₃ groups) on the surface of the hybrid material as well as the presence of disordered anatase-like structures. On the other hand, the acid and base properties are dependent on both HCl concentration and PDMS Mw. It has been observed that the acid and base parameters of the Si–Ti hybrid materials are influenced by the disorder degree of the amorphous titanium oxide present in them. As the disorder decrease both acid and base parameters increase.     

Unusual formation of β-carboline dimers under Bischler-Napieralski reaction conditions: an old reaction with a new direction

l-N-Formyl tryptophan methyl ester (3) underwent a Bischler-Napieralski reaction with POCl₃ at room temperature or under microwave irradiation, resulting in the unusual formation of β-carboline dimers 5 and 6. Most importantly, acetylation using Ac₂O of each of the dimers 5 and 6 separately afforded 1-[3′-carbomethoxy-β-carbolinyl]-3-carbomethoxy-9-acetyl-β-carboline (7) as the only product, the structure of which was confirmed by X-ray crystallography studies.     

One-pot three-component reaction; synthesis of new symmetrically bridge 4,4′-(1,4-phenylene)di-pyrimidines under solvent free conditions

The present article describes a facile one-pot synthesis of a new series of 4,4′-(1,4-phenylene)-dipyrimidines ( 6a–c and 10a, b ) by the reaction of terephthalaldehyde ( 1 ), 2-acetylthiophene, and/or nitriles with S-benzylthiouronium chloride 3a . And also, the di-pyrimidinones 13a-d were obtained by the reaction of different amidines 3a–d and ethyl cyanoacetate ( 11 ) with terephthalaldehyde ( 1 ) under solvent-free conditions in the existence of sodium hydroxide which is found to be a more efficient base for these reactions. The final products were characterized by spectral data and elemental analysis, IR, MS, ¹ H, and ¹³ C NMR spectroscopy.     

Effect of end groups on the raman spectra of lycopene and β-carotene under high pressure

The Raman spectra of all-trans-lycopene in n-hexane were measured under high pressure, and the results compared with those of β-carotene. The different pressure effects on Raman spectra are analyzed taking into account the different structures of lycopene and β-carotene molecules. It is concluded that: (a) the vibronic coupling between the S? and S? states of β-carotene is stronger than that of lycopene, (b) the diabatic frequency increment of the ν? mode is more susceptible to pressure than that of the ν? mode for lycopene, and (c) β-rings rotation can relieve the pressure effect on the C=C bond length in β-carotene. This work provides some insights for elucidating the structural and environmental effects on Raman spectra of carotenoids.     

KAl(SO4)2 · 12H2O (alum) a reusable catalyst for the synthesis of some 4-substituted coumarins via Pechmann reaction under solvent-free conditions

A simple, efficient, and practical procedure for the Pechmann condensation using KAl(SO₄)₂ · 12H₂O (alum) as a non-toxic, reusable, inexpensive, and easily available catalyst is described under solvent-free condition at 65°C. These improved reaction conditions allow the preparation of a wide variety of some new substituted coumarins in high yields (86–96%) and purity under mild reaction conditions. Compared to the classical Pechmann condensation, this new method consistently has the advantage of high yields. Correspondence: Ali A. Mohammadi, Department of Chemistry, Shahid Beheshti University, P.O. Box 19839-4716, Tehran, Iran.     

Catalytic oxidation of NO over Mn–Co–Ce–Ox catalysts: effect of reaction conditions

Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O₂. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h^?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O₂, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O₂ content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h.     

Enantioselective direct aldol reaction of α-keto esters catalyzed by (S(a))-binam-D-prolinamide under quasi solvent-free conditions

(S(a))-Binam-D-prolinamide (20 mol%), instead of (S(a))-binam-L-prolinamide, in combination with chloroacetic acid (100 mol%) is an efficient organocatalyst for the direct aldol reaction between α-keto esters as electrophiles and alkyl and α-functionalised ketones, under quasi solvent-free conditions, providing access to highly functionalised chiral quaternary γ-keto α-hydroxyesters with up to 92% ee.