Driving forces in substitution reactions of octahedral complexes: The influence of the competitive effect

The reaction of cis-[RuCl(2)(P-P)(N-N)] type complexes (P-P = 1,4-bis(diphenylphosphino)butane or (1,1`-diphenylphosphino)ferrocene; N-N = 2,2`-bipyridine or 1,10-phenantroline) with monodentate ligands (L), such as 4-methylpyridine, 4-phenylpyridine and benzonitrile forms [RuCl(L)(P-P)(N-N)](+) species Upon characterization of the isolated compounds by elemental analysis, (31)P{(1)H} NMR and X-ray crystallography it was found out that the type of the L ligand determines its position in relation to the phosphorus atom. While pyridine derivatives like 4-methylpyridine and 4-phenylpyridine coordinate trans to the phosphorus atom, the benzonitrile ligand (bzCN), a good pi acceptor, coordinates trans to the nitrogen atom. A (31)P{(1)H} NMR experiment following the reaction of the precursor cis-[RuCl(2)(dppb)(phen)] with the benzonitrile ligand shows that the final position of the entering ligand in the complex is better defined as a consequence of the competitive effect between the phosphorus atom and the cyano-group from the benzonitrile moiety and not by the trans effect. In this case, the benzonitrile group is stabilized trans to one of the nitrogen atoms of the N-N ligand. A differential pulse voltammetry experiment confirms this statement. In both experiments the [RuCl(bzCN)(dppb)(phen)]PF(6) species with the bzCN ligand positioned trans to a phosphorus atom of the dppb ligand was detected as an intermediate complex. (c) 2009 Elsevier Ltd. All rights reserved.

The mer-[RuCl(3)(dppb)(H(2)O)] complex: A versatile tool for synthesis of Ru(II) compounds

The complex mer-[RuCl(3)(dppb)(H(2)O)] [dppb = 1,4-bis(diphenylphosphino)butane] was used as a precursor in the synthesis of the complexes tc-[RuCl(2)(CO)(2)(dppb)], ct-[RuCl(2)(CO)(2)(dppb)]. cis-[RuCl(2)(dppb)(Cl-bipy)], [RuCl(2Ac4mT)(dppb)] (2Ac4mT = N(4)-meta-tolyl-2-acetylpyridine thiosemicarbazone ion) and trans-[RuCl(2)(dppb)(mang)] (mang = mangiferin or 1,3,6,7-tetrahydroxyxanthone-C2-beta-D-glucoside) complexes. For the synthesis of Run complexes, the Ru(III) atom in mer-[RuCl(3)(dppb)(H(2)O)] may be reduced by H(2)(g), forming the intermediate [Ru(2)Cl(4)(dppb)(2)], or by a ligand (such as H2Ac4mT or mangiferin). The X-ray structures of the cis-[RuCl(2)(dppb)(Cl-bipy)], tc-[RuCl(2)(CO)(2)(dppb)] and [RuCl(2Ac4mT)(dPpb)] complexes were determined. (C) 2010 Elsevier Ltd. All rights reserved.

On the synthesis and structures of the complexes [RuCl(L)(dppb)(N-N)]PF(6) (L = CO, py or 4-NH(2)py; dppb=1,4-bis(diphenylphosphino)butane; N-N=2,2 `-bipyridine or 1,10-phenanthroline) and [(dppb)(CO)Cl(2)-Ru-pz-RuCl(2)(CO)(dppb)] (pz = pyrazine)

The ""Ru(P-P)"" unit (P-P = diphosphine) is recognized to be an important core in catalytic species for hydrogenation of unsaturated organic substrates. Thus, in this study we synthesized six new complexes containing this core, including the binuclear complex [(dppb)(CO)Cl(2)Ru-pz-RuCl(2)(CO)(dPPb)] (pz = pyrazine) which can be used as a precursor for the synthesis of cationic carbonyl species of general formula [RuCl(CO)(dppb)(N-N)]PF(6) (N-N = diimine). Complexes with the formula (RuCl(py)(dppb)(N-N)]PF(6) were synthesized by exhaustive electrolysis of these carbonyl compounds or from the precursors [RuCl(2)(dppb)(N-N)]. The new complexes were characterized by microanalysis, conductivity measurements, IR and (31)P{(1)H)} NMR spectroscopy, cyclic voltammetry and X-ray crystallography. (C) 2010 Elsevier Ltd. All rights reserved.

Aerobic oxidation of monoterpenic alcohols catalyzed by ruthenium hydroxide supported on silica-coated magnetic nanoparticles

Ruthenium hydroxide supported on silica-coated magnetic nanoparticles was shown to be an efficient heterogeneous catalyst for the liquid-phase oxidation of a wide range of alcohols using molecular oxygen as a sole oxidant in the absence of co-catalysts or additives. The material was prepared through the loading of the amino modified support with ruthenium(III) ions from an aqueous solution of ruthenium(III) chloride followed by treatment with sodium hydroxide to form ruthenium hydroxide species. Characterizations suggest that ruthenium hydroxide is highly dispersed on the support surface, with no ruthenium containing crystalline phases being detected. Various carbonylic monoterpenoids important for fragrance and pharmaceutical industries can be obtained in good to excellent yields starting from biomass-based monoterpenic alcohols, such as isobomeol, perillyl alcohol, carveol, and citronellol. The catalyst undergoes no metal leaching and can be easily recovered by the application of an external magnet and re-used. (C) 2011 Elsevier Inc. All rights reserved.

A Ring Contraction Strategy toward a Diastereoselective Total Synthesis of (+)-Bakkenolide A

A diastereoselective route to (+)-bakkenolide A is presented from the readily available optically active Wieland-Miescher ketone. This novel synthesis of this sesquiterpene lactone features the following as key stereoselective transformations: (i) the ring contraction reaction of a octalone mediated by thallium(III) nitrate (TTN); (ii) a hydrogenation to create the cis-fused junction; and (iii) the formation of the C7 quaternary center through an enolate intermediate. Furthermore, during this work, the absolute configuration of a trinorsesquiterpene isolated from Senecio Humillimus was assigned.

Reduction kinetics of NiO-YSZ composite for application in solid oxide fuel cell

A porous nickel-8 mol% yttria stabilized zirconia (Ni-8YSZ) composite, used as anode for solid oxide fuel cell, was obtained by reduction of NiO-8YSZ cermet. The first goal was the evaluation of the temperature effect of powder processing by thermogravimetry. In addition, the influence of porosity in the reduction kinetic of the sample sintered at 1450 A degrees C was evaluated. The final porosity produced in NiO-8YSZ composite by pore former was 30.4 and 37.9 vol.%, respectively, for 10 and 15 mass% of corn starch. The sample with 15 mass% of corn starch promotes a reduction rate almost twice higher than sample with 10 mass% of corn starch. The porosity introduced by the reduction of NiO was 23 vol.%.

Group 11 (Cu, Ag, Au) promotion of 15%Co/Al(2)O(3) Fischer-Tropsch synthesis catalysts

Co/Al(2)O(3) Fischer-Tropsch synthesis catalysts promoted with different quantities of Group 11 metals (Cu, Ag, Au) were characterized and tested. The presence of relatively small quantities of such metals enhanced Co reducibility and, in the cases of Ag and Au, improved the surface Co metal active site densities. EXAFS experiments with the most loaded catalyst samples show that only Co-Co and Me-Me (Me = Cu, Ag and Au) coordination could be observed. This suggests that the greater fraction of the metals form different phases. However, the reduction promoting effect of the Group 11 metal is severely hampered once the catalyst receives a mild passivation treatment following primary reduction. An explanation in terms of promoter segregation during primary reduction is proposed. At lower promoter levels (0.83%Ag and 1.51%Au) and higher Ag levels (2.76%), significant gains in Co active site densities were achieved resulting in improved CO conversion levels relative to the unpromoted catalyst. Moreover, slight decreases in light product (e.g., CH(4)) selectivity and slight increases in C(5)+ selectivity were achieved. At high Au loading (5.05%), however, too much Au was loaded which, although significantly increasing the fraction of Co reduced, blocked Co surface sites and resulted in decreased Co conversion rates. While Cu facilitated Co reduction, the increased fraction of reduced Co did not translate to improved active site densities. It appears that a fraction of Cu tended to cover the rim of Co clusters, resulting in decreases in CO conversion rates and detrimental increases in light product selectivity. (C) 2009 Elsevier B.V. All rights reserved.

Kinetic and mechanistic investigation of the ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution

The ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution was investigated by determining the major reaction products and their evolution as a function of the reaction time and their dependence on the pH of the reaction system. 2,4-Dimethyl-nitrobenzene and 2,4-dimethyl-phenol were found to be primary reaction products; their formation might be explained by electron transfer and substitution reactions. 2,4-Dimethyl-phenol was further oxidized yielding 2,4-dimethyl- and/or 4,6-dimethyl-resorcinol by electrophilic addition of HO(center dot) radicals. The best fitting phenomenological kinetic model and the good convergence of calculated and experimentally determined rate constants imply two additional competitive pathways of substrate oxidation: (i) electrophilic addition of HO(center dot) radicals and fast subsequent substitution would also yield the resorcinol derivatives. (ii) Substrate and isolated products are thought to be oxidized by hydrogen abstraction at the benzylic sites, but the corresponding products (alcohols, aldehydes, and carboxylic acids) could not be identified. Fe(II) was added to probe for the presence of H(2)O(2), but had no or only a minor effect on the kinetics of the ozonolysis. (c) 2009 Elsevier B.V. All rights reserved.

(+)- and (-)-Mutisianthol: First Total Synthesis, Absolute Configuration, and Antitumor Activity

The first synthesis of the natural product (+)-mutisianthol was accomplished in 11 steps and in 21% overall yield from 2-methylanisole. The synthesis of its enantiomer was also performed in a similar overall yield. The absolute configuration of the sesquiterpene (+)-mutisianthol was assigned as (1S,3R). Key steps in the route are the asymmetric hydrogenation of a nonfunctionalized olefin using chiral iridium catalysts and the ring contraction of 1,2-dihydronaphthalenes using thallium(III) or iodine(III). The target molecules show moderate activity against the human tumor cell lines SF-295, HCT-8, and MDA-MB-435.

Ligand-Assisted Preparation of Palladium Supported Nanoparticles: a Step toward Size Control

Supported nanoparticles (SNPs) with narrow size distribution were prepared by H(2) reduction of Pd(2+) previously bound, to ligand-modified silica surfaces. Interestingly, the size of the Pd SNPs was tuned by the ligand grafted on the support surface. Amino- and ethylenediamino-functionalized supports formed Pd(0) SNPs of ca. 6 and 1 nm, respectively. The catalytic properties of both Pd(0) SNPs were investigated.

Stereoselective synthesis of azetidine-derived glutamate and aspartate analogues from chiral azetidin-3-ones

The stereoselective syntheses of cis conformationally constrained glutamate and aspartate analogues, containing an azetidine framework were accomplished from (S)-N-tosyl-2-phenylglycine in moderate overall yields. The key steps in these syntheses involved an efficient Wittig olefination of an azetidin-3-one, followed by a highly stereoselective rhodium catalyzed hydrogenation. The route could also be applied to the synthesis of a trans glutamate analogue, since epimerization of cis to trans isomer could be performed using DBU in toluene at reflux. (C) 2008 Elsevier Ltd. All rights reserved.

Silver Nanoparticles Obtained in PAH/PAA-Based Multilayers by Photochemical Reaction

Carboxylic acid groups in PAH/PAA-based multilayers bind silver cations by ion exchange with the acid protons. The aggregation and spatial distribution of the nanoparticles proved to be dependent oil the process used to reduce the silver acetate aqueous solution. The reducing method with ambient light formed larger nanoparticles with diameters ranging from 4-50 nm in comparison with the reduction method using UV light, which gave particles with diameters of 2-4 nm The high toughness of samples reduced by ambient light is a result of two population distributions of particle sizes caused by different mechanisms when compared with the UV light process. According to these phenomena, a judicious choice of the spectral source call be used as a way to control the type and size of silver nanoparticles formed on PEMs. Depending on the energy of the light source, the Ag nanoparticles present cubic and/or hexagonal crystallographic structures, as confirmed by XRD. Beyond the kinetically controlled process of UV photoinduced cluster formation, the annealing produced by UV light allowed a second mechanism to modify the growth rates, spatial distribution, and phases.

Nanocatalysts for sustainable industrial processses

In Chapter 1, rhodium nanoparticles were supported on multiwalled carbon nanotubes (MWCNTs) and bound to the magnetic core-shell system Fe3O4@TiO2. The composite Fe3O4@TiO2-Rh-MWCNT and the intermediates were characterized by SEM, EDS and TEM. Their catalytic activity was studied using i) the hydrogenation transfer of nitroarenes and cyclohexene in the presence of hydrazine hydrate; ii) the reduction of 2-nitrophenol with NaBH4; and iii) the decoloration of pigments in the presence of hydrogen peroxide. The results were monitored by gas chromatography (i) and UV Visible (ii and iii). In the second chapter, the catalytic activity of six oxidovanadium(V) aroylhydrazone complexes, viz. [VOL1(OEt)][VOL1(OEt)(EtOH)] (1), [VOL2(OEt)] (2), [Et3NH][VO2L1] (3), [VO2(H2L2)]2·EtOH (4), [VOL1(µ -O)VOL1] (5) and [VOL2(µ -O)VOL2] (6) (H2L1 = 3,5-di-tert-butyl-2-hydroxybenzylidene)-2hydroxybenzohydrazide and H2L2 = 3,5-di-tert-butyl-2-hydroxybenzylidene)-2 aminobenzohydrazide), anchored on nanodiamonds with different treatments, was studied towards the microwave-assisted partial oxidation of 1-phenylethanol to acetophenone in the presence of tert-butyl hydroperoxide (TBHP) as oxidant. A high selectivity for acetophenone was achieved for the optimized conditions. The possibility of recycling and reuse the heterogeneous catalysts was also investigated. In chapter 3, the catalytic activity of gold nanoparticles supported at different metal oxides, such as Fe2O3, Al2O3 ZnO or TiO2, was studied for the above reaction. The effect of the support, quantity of the catalyst and temperature was investigated. The recyclability of the gold catalysts was also studied. In the last chapter, a new copper nanocomposite with functionalized mutiwalled carbon nanotubes (Cu-MWCNT) was synthesized using a microwave assisted polyol method. The characterization was performed using XRD and SEM. The catalytic activity of Cu-MWCNT was studied through the degradation of pigments, such as amaranth, brilliant blue, indigo, tartrazine and methylene blue.

Síntese e caracterização de espinélios a base de Cu, Fe e Cr para pigmentos cerâmicos

Inorganic pigment comprises a host lattice, which is part of the chromophore component (usually a transition metal cation) and possible components modifiers, which stabilize, add or restate the properties pigments. Among the materials with spinel, ferrites, and the chromite stand out, because they have broad technological importance in the area of materials, applicability, pigments, catalytic hydrogenation, thin film, ceramic tiles, among others. The present work, pigments containing CuFe2O4, CuCr2O4,e CuFeCrO4, were synthesized by a method that makes use of gelatin as organic precursor using their application to ceramic pigments. The pigments were characterized by X-ray diffraction (XRD), Infrared spectroscopy, scanning electron microscopy (SEM) spectroscopy in the UV-visible and Colorimetry. The results confirmed the feasibility of the synthetic route used, with respect to powders synthesized, there is the formation of spinel phase from 500°C, with an increase in crystallinity and the formation of other phases. The pigments were shown to be crystalline and the desired phases were obtained. The copper chromite have hues ranging from green to black according to the calcination temperature, while the copper chromite doped with iron had brownish. The ferrites showed copper color and darker brown to black, which may indicate an interesting factor because of the importance of black pigment

Estudo da influência de compostos recalcitrantes na remoção de matéria orgânica biodegradável no tratamento de efluente de refinarias de petróleo

Petroleum Refinery wastewaters (PRW) have hart-to-degrade compounds, such as: phenols, ammonia, cyanides, sulfides, oils and greases and the mono and polynuclear aromatic hydrocarbons: benzene, toluene and xylene (BTX), acenaphthene, nitrobenzene and naphtalene. It is known that the microrganisms activity can be reduced in the presence of certain substances, adversely affecting the biological process of wastewater treatment. This research was instigated due the small number of studies regarding to this specific topic in the avaiable literature. This body of work ims to evaluate the effect of toxic substances on the biodegradability of the organic material found in PRW. Glucose was chosen as the model substrate due to its biodegradable nature. This study was divided into three parts: i) a survey of recalcitants compounds and the removal of phenol by using both biological and photochemical-biological processes; ii) biomass aclimation and iii) evaluation of the inhibitory effect certain compounds have on glucose biodegradation. The phenol degradation experiments were carried out in an activity sludge system and in a photochemical reactor. The results showed the photochemical-biological process to be more effective on phenol degradation, suggesting the superioruty of a combined photochemical-biological treatment when compared with a simple biological process for phenol removal from industry wastewaters. For the acclimation step, was used an activated sludge from industrial wastewaters. A rapid biomass aclimation to a synthetic solution composed of the main inhibitory compouns fpund in a PRW was obtained using the following operation condition: (pH = 7,0; DO ≥ 2,0 mg/L; RS = 20 days e qH = 31,2 and 20,4 hours), The last part was consisted of using respirometry evaluation toxicity effects of selected compounds over oxygen uptake rate to adaptated and non adaptated biomass in the presence of inhibitory compounds. The adaptated sludge showed greater degration capacity, with lower sensibility to toxic effects. The respirometry has proved to be very practical, as the techiniques used were simple and rapid, such as: Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), and Volatile Suspended Solids (VSS). Using the latter it is possible to perform sludge selection to beggingthe process; thus allowing its use for aerobic treatment system`s behacior prediction