Search results for "SELECTIVITY"
showing 10 items of 1148 documents
Efficient Synthesis of Multifunctional Chelating Agents Based on Tetraazacycloalkanes
2018
An efficient route has been developed for the synthesis of multifunctional tetraazacycloalkanes (in particular 1,4,7,10-tetraazacyclotridecane) incorporating an aminomethyl pendant arm on the carbon skeleton. Starting from the appropriate C-functionalized bisaminal-protected intermediate, the target macrocycles were easily obtained by means of a step-by-step introduction of the desired functional groups onto the free primary amine group, followed by deprotection of the bisaminal intermediates. This straightforward and versatile synthetic approach paves the way for the design of a new family of multifunctional chelators.
Oppenauer Oxidation of Secondary Alcohols with 1,1,1-Trifluoroacetone as Hydride Acceptor
2007
1,1,1-Trifluoroacetone (2a) reacts as a hydride-acceptor in the Oppenauer oxidation of secondary alcohols (1) in the presence of diethylethoxyaluminum. The oxidant allows for selective oxidation of secondary alcohols in the presence of primary alcohols.
Preparation, Characterization and Photocatalytic Activity of TiO2 Impregnated with the Heteropolyacid H3PW12O40: Photo-assisted Degradation of 2-prop…
2009
Abstract Both commercial and home prepared TiO2 samples impregnated with tungstophosphoric acid (H3PW12O40) were prepared and used for the photo-assisted degradation of 2-propanol in gas–solid regime. The characterization results evidenced a good coverage of the polyoxometalate (POM) onto the surface of both types of TiO2 samples along with a marginal effect of the presence of ethanol or HCl during the POM impregnation step on the specific surface area, porosity, morphology, crystallinity and acidity of the samples. Propene was the main intermediate product found in 2-propanol photocatalytic degradation by using the samples containing POM as the photocatalyst, whereas propanone was mainly o…
Structural and morphological investigation of a cobalt catalyst supported on alumina-baria: effects of redox treatments on the activity in the NO red…
2004
Abstract Temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO) have been used to study the various cobalt species formed in a cobalt catalyst (Co 1 wt.%) supported on alumina-baria, with composition Al2O3(80 wt.%)–BaO (20 wt.%). The catalyst was synthesized by incipient-wetness impregnation of the support with a water solution of cobalt acetylacetonate and calcined at 550 °C for 5 h. In order to investigate the structure and morphology of the sample, XRD, BET and SEM analyses were performed. Depending on the temperature and nature of pre-treatment (reductive or oxidative) different Co species (Co3O4, Co3+, surface Co2+, CoAl2O4) were formed. Activity tests in the…
IM-5 zeolite for steam catalytic cracking of naphtha to produce propene and ethene. An alternative to ZSM-5 zeolite
2013
Steam catalytic cracking of naphtha in smaller FCC units can be considered an option to produce more ethene and propene. These units will operate at high reaction temperatures and in the presence of steam. The profitability of these units could be improved with the use of new catalysts with higher activity and hydrothermal stability, without compromising the selectivity to light olefins. We have explored the possibilities of IM-5 zeolite for high temperature steam catalytic cracking (SCC) of a naphtha, as an alternative to commonly used ZSM-5 zeolite. So, we compare the catalytic activity, the effect of operating variables of the process and the yields of interest products between the two z…
Synthesis of Densely Functionalised 5-Halogen-1,3-oxazin-2-ones byHalogen-Mediated Regioselective Cyclisation of N-Cbz-ProtectedPropargylic Amines: A…
2013
A very efficient synthesis of 5-halogen-1,3-oxazin-2-ones has been accomplished by the halocyclisation reaction of chiral nonracemic N-carbobenzyloxy (N-Cbz)-protected propargylic amines by using I-2, Br-2 and Cl-2 as electrophile sources. The nature of the halogen influences the reaction time and yield. However, in all cases the reaction is totally regioselective taking place through a 6-endo-dig process regardless of the nature of the halogen and of the substituents in the starting material. To rationalise the experimental results, theoretical studies at the B3LYP/6-311G* level have been performed.
Alkylation of Benzene with Short-Chain Olefins over MCM-22 Zeolite: Catalytic Behaviour and Kinetic Mechanism
2000
Abstract Benzene alkylation with ethene and propene has been carried out under liquid-phase reaction conditions over zeolites MCM-22, Beta, and ZSM-5. MCM-22 seems to be a good catalyst for benzene alkylation especially with propene, showing high activity and stability and good selectivity. Kinetic experiments show that alkylation with propene follows an Eley–Rideal type mechanism.
Selective oxidation of C3–C4 olefins over Mo-containing catalysts with tetragonal tungsten bronze structure
2009
Abstract Mo–V–Nb–P–O-based catalysts with a tetragonal tungsten bronze-type (TTB) structure have been prepared hydrothemally from a H 3 PMo 12 O 40 Keggin-type heteropolyacid. These catalysts have been tested in the oxidation of C 3 –C 4 olefins (propene, isobutene and 1-butene). Although the catalytic performance depends on the nature of the olefin fed the TTB-type catalysts prepared in the presence of elements of the V and VI groups such as Te, Sb and Bi have shown a high selectivity to partial oxidation products, especially that with Te. However, in the absence of these elements the TTB-catalysts present a high catalytic activity to deep oxidation. The selectivity to partial oxidation pr…
Highly regio- and stereoselective iodocyclization of chiral 3-alkoxycarbonyl-4-propenyl-2,2-dimethyl-1,3-oxazolidines: a computational investigation
1999
The iodocyclization of allylic carbamates 3a and 3b proceeded with high regio- and stereoselection to give 2-oxobicyclo[4.3.0]nonane 5a as the major product. Both the regio- and diastereoselection of the reaction were investigated with the help of molecular mechanics and quantomechanical calculations. The energetic difference between the competing transition states TS-5a and TS-5b is in good agreement with the experimental results and from the calculated transition structures it appears that steric factors direct the discrimination.
Antiproliferative Properties of a Few Auranofin-Related Gold(I) and Silver(I) Complexes in Leukemia Cells and their Interferences with the Ubiquitin …
2020
A group of triethylphosphine gold(I) and silver(I) complexes, structurally related to auranofin, were prepared and investigated as potential anticancer drug candidates. The antiproliferative properties of these metal compounds were assessed against two leukemia cell lines, i.e., CCRF-CEM and its multidrug-resistant counterpart, CEM/ADR5000. Interestingly, potent cytotoxic effects were disclosed for both series of compounds against leukemia cells, with IC50 values generally falling in the low-micromolar range, the gold derivatives being on the whole more effective than the silver analogues. Some initial structure-function relationships were drawn. Subsequently, the ability of the study compo…