Chromium Trioxide Supported onto Wet Silica Gel: Rapid Oxidation of Alcohols to Carbonyl Compounds Under Microwave Irradiation in Solventless System

In an environmentally benign system, alcohols are rapidly oxidized to carbonyl compounds using CrO 3 supported onto wet silica gel as an oxidant under microwave irradiation.     

Microwave Thermolysis: A Rapid and Selective Method for the Cleavage of THP Ethers Using CrO 3 Supported onto Zeolite in Solventless System

Oxidative deprotection of tetrahydropyranyl ethers (THP ethers) using chromium trioxide supported onto zeolite under microwave irradiation in solvent free condition is described.     

The effect of cell orientations and environmental conditions on the performance of a passive DMFC single cell

A single cell passive air-breathing liquid feed direct methanol fuel cell (DMFC) is designed and fabricated. Furthermore, the effects of cell orientation and environmental conditions such as temperature and relative humidity on the performance of such passive DMFC are tested experimentally. The obtained results indicate that both environmental temperature and relative humidity have significant effects on the performance of fabricated fuel cell. The experimental data contained within this work shows that under lower relative humidity and higher temperature, the passive air-breathing direct methanol fuel cell has higher power output and better performance. According to experimental results, flooding has a vital role on the cell performance in various relative humidity and temperatures. The results also show that cell orientation has a strong effect on the performance of passive DMFC. The best power output and performance were achieved under vertical orientation.     

All alkoxide route to manganate and coboltate perovskite films and powders: effects of processing parameters

Manganate and cobaltate perovskites having the general formula ABO₃ have many technologically important applications. Here we present all alkoxide based routes to manganate and coboltate perovskite films and nano-phase powders of the compositions; LCMO (La_0.67Ca_0.33MnO₃), LSMO (La_0.75Sr_0.25MnO₃), LNCMO (La_0.33Nd_0.33Ca_0.33MnO₃), LBSMO (La_0.75Ba_0.125Sr_0.125MnO₃) and LSCO (La_0.50Sr_0.50CoO₃). The Mn and Co (oxo) methoxy-ethoxide precursors were prepared by reaction of MnCl₂ or CoCl₂ with 2 Kmoe in methoxy-ethanol-toluene. After hydrolysis of the alkoxide solutions by atmospheric air all systems produced X-ray and electron diffraction amorphous gels of high elemental homogeneity, and the IR spectra showed that they consisted of hydrated oxo-carbonates. Heating in air resulted in similar weight-loss curves for all studied gels passing; loss of H₂O in the range 20–300 °C, decomposition of carbonate groups into oxide and CO₂ in the temperature range 300–700 °C, and in some cases loss of a small amount of oxygen in the temperature range 700–1,000 °C. The pure perovskites were obtained at 690–770 °C with heat rates of typically 5–20 °C min^?1 without annealing. Perovskites could also be obtained at 550 °C by annealing, but these perovskites are prone to be A-site ion inhomogeneous according to the TEM EDS studies, which was not the case for the perovskites heat-treated to at least the carbonate decomposition temperature. This A-site inhomogeneity is ascribed to sequential decomposition of carbonates due to their different thermal stabilities, which is probably a general feature also with other sol–gel precursors and low temperature annealing. High quality polycrystalline films were prepared on Si/SiO₂/TiO₂/Pt substrates with all compositions and high quality epitaxial films were prepared of LCMO (on 100 LaAlO₃) and LSCO (on 100 SrTiO₃). The colossal magneto resistance (CMR) of the epitaxial LCMO films of 32% (246 K) is in parity with PLD derived films. The conductivities of the epitaxial and polycrystalline LSCO films were 1.9 mΩcm (on STO) and 1.7 mΩcm (on α-Al₂O₃, respectively).     

Solid State Desemicarbazonation on Clayfen Under Microwave Irradiation

Summary.  A new, efficient, and environmentally benign method for the cleavage of semicarbazones has been achieved by a simple reaction of semicarbazones with clayfen under microwave irradiation. Received January 4, 2001. Accepted (revised) March 1, 2001     

Dess-Martin Periodinane on Silica: Rapid Oxidation of Alcohols using Microwaves

Adsorbed on silica gel. Dess-Martin periodinane can rapidly oxidize alcohols to the corresponding carbonyl compounds upon exposure to microwave under solvent-free condition.     

A new chromium (III) complex containing N-(2-pyridylmethyl)-2-pyrazinecarboxamide, (NPyPzCa): Synthesis,molecular and crystal structure and theoretical electron density analysis

The chromium (III) complex [Cr(NPyPzCa)Cl₂(H₂O)].(CH₃)₂O (1) (NPyPzCa stands for N-(2-pyridylmethyl)-2-pyrazinecarboxamide) has been synthesized and characterized by single crystal X-ray diffraction. The Cr(III) atom exhibits an octahedral geometry due to the coordination of three donor atoms from carboxamide ligand, two chlorine atoms and one water molecule. There is O–H?O hydrogen bonds and also π–π interactions between adjacent pyridine and ?pyrazine rings that seem to be effective in the stabilization of the crystal packing. The ?topological and energetic properties of the electron density distribution of all the metal–ligand ?bonding interactions in this complex have also been calculated and studied at ? several DFT levels. According to the results, metal–ligand bonding interactions belong (from the topological and energetic point of view) to new interactions that represent a mix of closed-shell (ionic) and shared (covalent) characters.     

Theoretical and experimental study of molecular structure and vibrational spectra of N -(2-pyridylmethyl)-2-pyrazinecarboxamide

N-(2-Pyridylmethyl)-2-pyrazinecarboxamide was prepared and its crystal structure was investigated by X-ray analysis. The compound crystallizes in the triclinic space group P[`1]P{\bar 1} with a = 4.262(3), b = 12.117(9), c = 20.840(18) ?, α = 91.802(6), β = 89.834(7), γ = 91.845(6)°, V = 1075.2(16) ?³, Z = 4, and D = 1.323 Mg/m³. The structure was solved by direct method and refined to R = 0.0699 and wR ₂ = 0.1268 by full matrix anisotropic least-squares method. Using the Hartree-Fock and density functional method (B3LYP) with 6-31G(d) basis set, the molecular geometry and vibrational frequencies of the title compound has been investigated and compared with experimental ones from experimental studies. The optimized bond lengths obtained by RHF method and bond angles obtained by B3LYP method show better agreement with the experimental values. The vibrations computed of the title compound by the RHF and DFT methods are in good agreement with the observed IR spectra data.     

Theoretical and experimental study of molecular structure and vibrational spectra of <Emphasis Type="Italic">N</Emphasis>-(2-pyridylmethyl)-2-pyrazinecarboxamide

N-(2-Pyridylmethyl)-2-pyrazinecarboxamide was prepared and its crystal structure was investigated by X-ray analysis. The compound crystallizes in the triclinic space group \(P{\bar 1}\) with a = 4.262(3), b = 12.117(9), c = 20.840(18) Å, α = 91.802(6), β = 89.834(7), γ = 91.845(6)°, V = 1075.2(16) ų, Z = 4, and D = 1.323?Mg/m³. The structure was solved by direct method and refined to R = 0.0699 and wR ₂ = 0.1268 by full matrix anisotropic least-squares method. Using the Hartree-Fock and density functional method (B3LYP) with 6-31G(d) basis set, the molecular geometry and vibrational frequencies of the title compound has been investigated and compared with experimental ones from experimental studies. The optimized bond lengths obtained by RHF method and bond angles obtained by B3LYP method show better agreement with the experimental values. The vibrations computed of the title compound by the RHF and DFT methods are in good agreement with the observed IR spectra data.