Search results for "Propane"
showing 10 items of 486 documents
In Vitro Percutaneous Penetration of Acyclovir from Solvent Systems and Carbopol 971-P Hydrogels: Influence of Propylene Glycol
2005
The mechanism underlying propylene glycol (PG) effects on acyclovir (ACV) penetration through human epidermis were studied. Solvent systems and Carbopol gels containing increasing percentage of PG (from 0% to 70%, w/w) were used. Viscosity studies of both vehicles were carried out to characterise the influence of rheological behaviour. In solvent systems skin permeation values of ACV increase as the concentration of PG increase yielding a maximum enhancement ratio (ER = 10) for 70% PG. The release rate of ACV from gels was determined. Higuchi's model was used to estimate the apparent diffusion coefficient of the drug. These values show a decrease as the content of PG in the vehicle increase…
Cracking of n-heptane on a hzsm-5 zeolite. The influence of acidity and pore structure
1985
Abstract The crackino of n-heptane on a HZSM-5 zeolite has been studied in a continuous qlass flow reactor, at atmospheric pressure, up to 470°C. The initial selectivities to the different reaction products, kinetic rate constants, activation energies and decay parameters have been calculated and compared with those obtained using a large pore zeolite (HYUS). A different product distribution is obtained with the two zeolites. In that way, and considering initial selectivities, different C 6 /C 1 , C 5 /C 2 , C 4 /C3, i-C 4 /n-C 4 , ethylene/ethane, propylene/propane ratios have been found on the two zeolite catalysts. The results have been quantitatively explained by considerinq a direct cr…
Diastereoselective synthesis of antiquorin and related polyoxygenated atisene-type diterpenes
2007
Abstract A diastereoselective approach to polyoxygenated atisene-type diterpenes starting from (S)-(+)-carvone is described. The key steps used in the preparation of the atisene framework are an intramolecular Diels–Alder reaction, an intramolecular diazoketone cyclopropanation, an endocyclic cyclopropane ring cleavage and the regioselective reduction of an allylic bromide by a low-valent chromium species. The synthesis of natural atisanes antiquorin (1), atis-16-ene-3,14-dione (3), atis-16-ene-2,3,14-trione (8) and 3β-hydroxy-atis-16-ene-2,14-dione (9) following this approach is presented. Also described is the synthesis of 18-hydroxy-atis-16-ene-3,14-dione (5), the structure erroneously a…
Selective oxidation of propane over alkali-doped Mo-V-Sb-O catalysts
2009
[EN] Alkali metal-doped MoVSbO catalysts have been prepared by impregnation of a MoVSbO-mixed oxide (prepared previously by a hydrothermal synthesis) and finally activated at 500 or 600 degrees C in N-2. The catalysts have been characterized and tested for the selective oxidation of propane and propylene. Alkali-doped catalysts improved in general the catalytic performance of MoVSbO, resulting more selective to acrylic acid and less selective to acetic acid than the corresponding alkali-free MoVSbO catalysts. However, the specific behaviour strongly depends on both the alkali metal added and/or the final activation temperature. At isoconversion conditions, catalysts activated at 600 degrees…
CCDC 817805: Experimental Crystal Structure Determination
2011
Related Article: M.Sarwar, A.M.Madalan, F.Lloret, M.Julve, M.Andruh|2011|Polyhedron|30|2414|doi:10.1016/j.poly.2011.06.011
Chemical and Spectroscopical Properties of Medium Sizedtrans- andcis-Bicyclo[n.1.0]alk-2-ynes
1997
Chemical and spectroscopical properties of cis- and trans-cyclopropano-anellated cycloalkynes of medium ring size are investigated and compared with results from force field calculations. IR and 13C-NMR data of the alkynes reflect the deformation of the triple bond due to ring strain. Parallel to bending the reactivity increases with decreasing ring size, the trans fused alkynes prove to be nearly as reactive as the cis fused with a two carbon smaller ring size. The bicycloalkynes are complexed with silver triflate. 13C NMR reveals that the triple bond as well as the cyclopropane serve as ligands.
Density Functional Theory Study on Propane and Propene Adsorption on Pt(111) and PtSn Alloy Surfaces
2011
Density functional theory calculations were performed to investigate the adsorption of propane, propene, and C and H atoms on Pt and PtSn surfaces employing the revised Perdew–Burke–Ernzerhof (RPBE) and vdW-DF functionals. Propane adsorption was found to be mediated by van der Waals interactions without significant site preference on any of the studied surfaces. The adsorption characteristics of propene are different: On the Pt(111) and Pt3Sn(111) surfaces, propene adsorption is covalent, and the molecule prefers a di-σ site to a π site. Alloying Pt(111) with Sn leads to weaker adsorption owing to geometric and relaxation effects, whereas electronic effects are found to be small. On the PtS…
Oxidative dehydrogenation of propane and n-butane on V-Mg based catalysts
1994
Abstract The catalytic properties of vanadium supported catalysts for the oxidative dehydrogenation of propane and n-butane has been studied. Natural Sepiolite and magnesium oxalate were used as starting support materials. Large differences in the type of crystalline phases were detected on the calcined catalysts depending on the vanadium content and nature of the support. The active and selective sites for the oxidative dehydrogenation of propane and n-butane, are related with isolated V 5+ with atetrahedral coordination. The presence of vanadium species with coordination higher than 4 negatively influence the selectivity to dehydrogenation products.
A DFT study of the mechanism of Brønsted acid catalysed Povarov reactions
2015
Abstract The molecular mechanism of the Bronsted acid (BA) catalysed Povarov reaction of N -phenyl- C -methoxycarbonyl imine with a methylenecyclopropane (MCP) has been investigated using DFT methods at the MPWB1K/6-31G(d) level. This BA catalysed Povarov reaction is a domino process initialised by the formation of a cationic intermediate which experiences a quick intramolecular Friedel–Crafts reaction yielding the final tetrahydroquinoline. Protonation of the imine nitrogen atom notably increases the electrophilicity of the corresponding species, accelerating the reaction through ionic processes. Analysis of the Parr functions in the initial nucleophilic attack of MCP to the protonated imi…
The role of metal oxides as promoters of V2O5/γ-Al2O3 catalysts in the oxidative dehydrogenation of propane
1997
Summary The physicochemical properties of potassium-, bismuth-, phosphorous- and molybdenum-doped (Me/V atomic ratios of 0 to 1) V 2 O 5 /γ-Al 2 O 3 catalysts and their catalytic behavior in the oxidative dehydrogenation of propane have been compared. The incorporation of metal oxides modifies the catalytic behavior of alumina-supported vanadia catalysts by changing both their redox and their acid-base properties. In this way, the addition of potassium leads to the best increase in the selectivity to propylene. This performance can be related to the modification of the acid character of the surface of the catalysts. The possible role of both redox and acid-base properties of catalysts on th…