Lipopolysaccharides of marine blue-green algae

The lipopolysaccharides (LPSs) have been isolated from two blue-green algae,Oscillatoria hilderbrandtii andNostoc sp. by the method of phenol-water extraction. The LPSs contain polysaccharide and lipid components. The polysaccharide fraction fromO. hildebrandtii consists predominantly of 1,3-bound rhamnose residues with a substituent in the second position. The rhamnose residues in the polysaccharide fraction ofNostoc are connected by 1,3- and 1,2-glycosidic bonds. The lipid components of the LPSs fromO. hilderbrandtii andNostoc consist of palmitic and steric acids, with glucosamine and glucose.     

Catalytic Synthesis of D‐Glucosaminic Acid from D‐Glucosamine on Active Charcoal‐Supported Pd‐Bi Catalysts

D‐Glucosaminic acid (2‐amino‐2‐deoxy‐D‐gluconic acid), is a component of bacterial lipopolysaccharides, sweetener, condiments, and a chiral synthon. A catalytic oxidation of D‐glucosamine to D‐glucosaminic acid by molecular oxygen on active charcoal‐supported Pd‐Bi catalysts is described in good yield.     

Formation of C4 Oligomers in Hydrogenation of Acetylene over Pd/Al2O3 and Pd/TiO2 Catalysts

Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/-alumina and 0.5 wt.% Pd/TiO₂catalysts. Non-steady-state regime of catalyst operation was tested in pulse-flow experiments. Significant carbon poisoning appears to be a necessaryrequisite for selective formation of ethylene. The effect of hydrogen and acetylene partial pressure has been tested on the selectivity of C₄products. At 273–298 K the catalysts showed 26–35% selectivity for C₄ hydrocarbons and <2.5% for ethane production at conversionsof 30–40%. Deuterium distribution in ethylene and 1,3-butadiene and the deuterium content of the surface hydrogen pool have been compared and mechanismof diene formation has been discussed.     

Oxidation of propylene glycol and lactic acid to pyruvic acid in aqueous phase catalyzed by lead-modified palladium-on-carbon and related systems

Oxidation of propylene glycol and related compounds to pyruvic acid was carried out in aqueous phase at 90 °C with a controlled pH of 8 in the presence of Pd/C modified by Pb, Bi and/or Te as additives. Oxidation of propylene glycol was observed on Pd/C at both the primary and secondary hydroxyl groups to yield lactic acid, hydroxyacetone and pyruvic acid with low selectivities. Pd/C, which alone was inactive in the oxidation of lactic acid, bound Pb on the metallic Pd with a strong interaction. The resultant Pb/Pd/C revealed activity for the selective conversion of lactic acid into pyruvic acid. A trace amount of the additive Pb as low as the atomic ratio Pb/Pd = 0.05, was enough to afford pyruvic acid, and the initial rate of the oxidation showed a maximum at Pb/Pd=0.3. Similar catalysts gave results as follows: Pb/Pt/C, highly active, but less selective; Te/Pd/C, highly selective to pyruvic acid with mild activity; Bi/Pd/C, moderate in both activity and selectivity. Commercially available Pb/Pd/CaCO₃ (Lindlar catalyst) and Pb/Pd/Al₂O₃ were also active, giving 60% yield of pyruvic acid.     

A practical synthesis of highly functionalized aryl nitriles through cyanation of aryl bromides employing heterogeneous Pd/C: in quest of an industrially viable process

Preparation of aryl nitrile 2a through classical Rosenmund-von Braun reaction of aryl bromide 1a resulted in a poor yield (61%) due to a high reaction temperature (165 °C) and a lack of efficient procedure for separating 2a from a large quantity of heavy metal waste (Cu salts). To address these issues, a practical synthesis of multifunctional aryl nitriles through cyanation of aryl bromides has been developed with heterogeneous Pd/C used as the catalyst. Treatment of aryl bromides 1 with Zn(CN)₂ in the presence of Pd/C, Zn, ZnBr₂ and PPh₃ in DMA provided aryl nitriles 2 involving those carrying sterically demanding electron-rich substituent in good yields and in highly reproducible manner. The activity of Pd/C is highly dependent on the properties of the Pd/C. Oxidic thickshell type catalyst Pd/C D5 was found to furnish the highest rate acceleration and yield. The use of heterogeneous Pd/C might anchor and disperse Pd over the solid support of the catalyst, at least in the initial stage of the reaction, to assure the formation of monomeric Pd complex without precipitating to inactive Pd black. The use of a slightly excess of Zn(CN)₂ (0.6 equiv) and air oxidation of phosphine ligand, after end of the reaction, converted Pd species to insoluble phosphine-free Pd cyanides, from which Pd was recovered in high yield through simple filtration followed by usual recovery process involving combustion.     

Effect of oxidative treatment on the colloid-chemical properties of lignosulfonates

The effect of oxidative treatment on colloid-chemical properties of lignosulfonates was studied. Oxidation of lignosulfonates (403–423 K, $P_{O_2 } $ = 0.2–0.8 MPa, 0.5–1 h) is accompanied by a decrease in the content of hydroxy groups and by an increase in the content of carbonyl groups in oxidation products. Under severe oxidation conditions (423–433 K, $P_{O_2 } $ = 0.8 MPa, 3 h), lignosulfonates undergo chemical degradation with the formation of lower carboxy derivatives. The oxidized lignosulfonates exhibit lower performance, compared to the initial samples, in wetting and dispersion of sphalerite and elemental sulfur.     

Bifidobacterium longum l-Arabinose Isomerase—Overexpression in Lactococcus lactis, Purification, and Characterization

Bifidobacterium longum NRRL B-41409 l-arabinose isomerase (l-AI) was cloned and overexpressed in Lactococcus lactis using a phosphate-depletion-inducible expression system. The purified B. longum l-AI was characterized using d-galactose and l-arabinose as the substrates. The enzyme was active and stable at acidic pH with an optimum at pH 6.0?C6.5. The enzyme showed the highest activity at 55?°C during a 20-min incubation at pH 6.5. The K _m value was 120?mM for l-arabinose and 590?mM for d-galactose. The V _max was 42?U mg^?1 with l-arabinose and 7.7?U mg^?1 with d-galactose as the substrates. The enzyme had very low requirement for metal ions for catalytic activity, but it was stabilized by divalent metal ions (Mg²⁺, Mn²⁺). The enzyme bound the metal ions so tightly that they could not be fully removed from the active site by EDTA treatment. Using purified B. longum l-AI as the catalyst at 35?°C, equilibrium yields of 36?% d-tagatose and 11?% l-ribulose with 1.67?M d-galactose and l-arabinose, respectively, as the substrates were reached.     

钯催化 1,3-丁二烯羧酯化合成 3-戊烯酸甲酯

 以 1,3-丁二烯、CO 和甲醇为原料, 进行羧酯化反应合成 3-戊烯酸甲酯是 Altam 路线生产己内酰胺绿色工艺的关键步骤. 将 Pd 与三齿 N-杂环配体或双膦配体组成的催化体系用于 1,3-丁二烯的羧酯化反应中, 其中乙酸钯/2,6-二 (3,5-二甲基吡唑基) 吡啶催化剂表现出中等的催化活性, 在 150 ºC, p(CO) = 6.0 MPa 的优化条件下反应 6 h, 1,3-丁二烯转化率为 78.8%, 3-戊烯酸甲酯选择性达 92.2% (TON = 226); 而乙酸钯/2,2?-二 (二苯基膦基) 苯醚催化体系的活性更高, 在优化反应条件下, 1,3-丁二烯转化率达 90.4%, 3-戊烯酸甲酯选择性为 91.6% (TON = 181). 在 200 ºC 及类似的羧酯化反应条件下, 1,3-丁二烯发生二聚反应, 其转化率为 99% 以上, 二聚产物 4-乙烯基-1-环己烯选择性高于 96%.     

Investigation of thermal and catalytic degradation of polystyrene waste into styrene monomer over natural volcanic tuff and Florisil catalysts

Thermal and catalytic degradation of polystyrene waste over two different samples of natural volcanic tuff catalyst comparative with Florisil catalyst has been carried out in order to establish the conversion degree into styrene monomer. The polystyrene waste (PS) was subjected to a thermal degradation process in the range of 380–500°C in presence of studied catalysts in a ratio of 1/10 in mass, catalyst/PS. The catalysts were characterized by N₂ adsorption-desorption isotherms (BET), Scanning Electron Microscopy (SEM) and Fourier-transform infrared spectrometry (FTIR). Influences of temperature and type of catalysts on the yields and on the distribution of end-products obtained by thermal and catalytic degradation of polystyrene waste have been studied. The maximum yields of liquid products were obtained at 460°C degradation temperature and were calculated between 83.45% and 90.11%. The liquid products were characterized by gas chromatography mass spectrometry (GC-MS) and FTIR analytical techniques. The GC-MS results showed that the liquid products contained styrene monomer up to 55.62%. The FTIR spectra of liquid products indicated the specific vibration bands of the functional groups of compounds of liquid products. The amounts of styrene monomer obtained were influenced by structural and textural properties of studied catalyst and the contribution on product distribution is discussed.      

New insights into the palladium-catalysed synthesis of δ-lactones from 1,3-dienes and carbon dioxide

Two-coordinate Pd(0) complexes are shown to be important intermediates in the telomerization of 1,3-dienes and CO₂ using palladium/phosphine catalysts without additives. Only one phosphorus atom is bound to palladium during the C–C bond forming steps, but the second phosphorus atom is crucial in the early stages of the catalytic cycle and for the elimination of the product. A ligand that gave an active palladium catalyst for the coupling of 1,3-butadiene and CO₂ has been designed. Use of a palladium catalyst in the reaction of isoprene with CO₂ allowed for the first time isolation and NMR spectroscopic characterization of the resulting mixture of lactones.     

ISOMERIZATION OF 2-PHOSPHA-4-SILA-BICYCLO[1.1.0]BUTANE

In analogy with the valence isomerism of the hydrocarbons bicyclobutane, 1,3-butadiene and cyclobutene, the rearrangements for 2-phospha-4-sila-bicyclo[1.1.0]butane were studied at the B3LYP/6-311+G** G**basis set was employed throughout for the geometry optimizations. First and second order energy derivatives were computed to confirm the nature of the minima and transition structures. Intrinsic reaction coordinate calculations (IRC) were performed to establish connections between transition structures and minima. level of theory. The monocyclic 1,2-dihydro-1,2-phosphasilete is shown to be the thermodynamically preferred product, in contrast to the isomerism of the hydrocarbons that favors the 1,3-butadiene structure.     

An efficient glucose-based ligand for Heck and Suzuki coupling reactions in aqueous media

The glucose-based ligand, N-salicylidene-d-glucosamine (Sal-d-glsmN), was readily obtained by reaction of salicylaldehyde (Hsal) with the d-glucosamine hydrochloride. Ligand Sal-d-glsmN was found to be an efficient ligand in the palladium-catalyzed Suzuki and Heck C–C coupling reactions in aqueous medium under aerobic condition. It was found that the use of Sal-d-glsmN/Pd(OAc)₂ system as a catalyst, aryl halides undergo Suzuki and Heck cross-couplings, respectively, with arylboronic acids and olefins to give the desired products in moderate to excellent yields.     

Comparative studies of Pd, Ru, Ni, Cu/ZnAl2O4 catalysts for the water gas shift reaction

The activity of monometallic Pd, Ru, Ni and Cu catalysts supported on spinel ZnAl₂O₄ for water gas shift reaction (WGS) was investigated. The physicochemical properties of each catalyst was studied by XRD, TPR, BET and chemisorption methods. The highest activity was obtained for Cu/ZnAl₂O₄ among the catalysts tested. The activation process carried out in a reducing atmosphere 5%H₂-95%Ar in the case of Cu/ZnAl₂O₄ system lead to the catalytic activity improvement. In the case of copper catalysts, the water gas shift reaction proceeded by the redox surface mechanism between Cu⁰/Cu⁺. The PdZn alloy formation after reduction at 350°C was shown.      

Tentative explanation for the kinetic compensation effect in doped catalysts

The kinetic parameter compensation effect displayed by heterogeneous catalysts may occur when the global reaction is a combination of competing reactions which show the same mechanism and take place on different groups of active centres, each group showing different activation energy and pre-exponential factor values. In this study, a simple procedure is described for employing apparent kinetic data (lnA and E _a) that show a compensation effect in order to calculate the activation energies and pre-exponential factors (proportional to the population densities) of active centres that present equal reaction mechanisms in dual site catalysts. The procedure was used to reproduce apparent kinetic data taken from the literature and obtained from experiments with doped-catalysts prone to dual-site catalytic behaviour. The fittings obtained in all cases were very good. The population density of active centres with $E_{a_2 }$ activation energy showed constant growth with the increase in doping agent content, whereas that of the active centres originally present in the undoped catalysts $\left( {E_{a_1 } } \right)$ showed varying trends.     

Preparation of Pd/C catalyst for formic acid oxidation using a novel colloid method

A novel colloid method using (WO₃)_n·xH₂O as colloidal source was developed to prepare Pd/C catalyst for formic acid oxidation. Transmission electron microscopy image shows that the Pd/C nanoparticles have an average size of 3.3 nm and a narrow size distribution. Electrochemical measurements indicate that the Pd/C catalyst exhibits significantly high electrochemical active surface area and high catalytic activity with good stability for formic acid oxidation compared with that prepared by common method. The colloid method is very simple and has great potentials for mass-producing Pd/C and others noble metal catalysts.     

New Synthesis of β-Anilinochalcones by Regioselective Oxidation of β-Anilinodihydrochalcones Using Iodine–DMSO

β-Anilinodihydrochalcones readily undergo oxidation α to the carbonyl group region in the presence of a catalytic amount of iodine in dimethyl sulfoxide at 130 °C in good yield. Oxidation of allyloxy-substituted β-anilinodihydrochalcones to β-anilinochalcones is a preferred reaction over deallylation.     

Catalytic reduction of sulfuric acid to sulfur dioxide

The reduction of H₂SO₄ to SO₂ occurs with a relatively good efficiency only at high temperatures, in the presence of catalysts. Some experimental results, regarding conversion of sulfuric acid (96 wt.%) to sulfur dioxide and oxygen, are reported. The reduction has been performed at 800 ?C 900°C and atmospheric pressure, in a tubular quartz reactor. The following commercial catalysts were tested: Pd/Al₂O₃ (5 wt.% and 0.5 wt.% Pd), Pt/Al₂O₃ (0.1 wt.% Pt) and ??-Fe₂O₃. The fresh and spent catalysts were characterized by X-Ray diffraction and BET method. The highest catalytic activity was determined for 5 wt.% Pd/Al₂O₃, a conversion of 80% being obtained for 5 hours time on stream, at 9 mL h^?1 flow rate of 96 wt.% H₂SO₄. A conversion of 64% was determined for 0.5 wt.% Pd/Al₂O₃ and 0.1 wt.% Pt/Al₂O₃. For ??-Fe₂O₃, a less expensive catalyst, a conversion of 61% for about 60 hours was obtained.      

Oxidation of d-Glucose by Silver(III) Periodate Complex in the Presence of Ru(III)/Os(VIII) as a Homogeneous Catalyst: A Comparative Mechanistic Study (Stopped Flow Technique)

The kinetics of the oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalyzed oxidation of d-glucose (d-Glu) by silver(III) periodate complex (DPA) in aqueous alkaline medium at 298 K and constant ionic strength 0.003 mol·dm^?3 was studied spectrophotometrically. The reaction between d-Glu and DPA in alkaline medium exhibits 1:2 stoichiometry in both catalyzed reactions (d-Glu:DPA). The main products were identified as D-arabinonic acid and formic acid by spot tests, GC–MS spectra and chromatographic techniques. The reaction orders with respect to various species concentrations were determined. Also, the active species of catalyst and oxidant have been identified. Probable mechanisms were proposed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order Os(VIII) > Ru(III).     

Effect of the Structure of Carbon Nanofibers on the State of an Active Component and on the Catalytic Properties of Pd/C Catalysts in the Selective Hydrogenation of 1,3-Butadiene

The state of highly dispersed palladium particles supported on filamentous carbon was studied using high-resolution electron microscopy, XPS, and X-ray diffraction analysis. Three types of filamentous carbon were used, in which the basal planes of graphite were arranged along, across, and at an angle to the nanofiber axis. The amount of supported palladium was 0.25–5.8 wt %. The structure of the carbon support was found to affect the properties of the active component. Highly dispersed palladium particles exhibited the strongest interaction with a carbon surface formed by the butt ends of graphite (002) layers. This interaction resulted in electron transfer from the metal to the support and in the stabilization of palladium in the most dispersed state. A change in the properties of palladium particles caused a change in the catalytic properties of Pd/C catalysts in the reaction of selective 1,3-butadiene hydrogenation to butenes. The strong interaction of Pd²⁺ with the butt ends of graphite resulted in the stabilization of palladium in an ionic state. An increase in the fraction of Pd²⁺ in the catalysts was responsible for a decrease in both the overall activity and selectivity of Pd/C catalysts in the reaction of 1,3-butadiene hydrogenation to butenes.     

The role of hypervalent iodine(iii) reagents in promoting alkoxylation of unactivated C(sp3)–H bonds catalyzed by palladium(ii) complexes

Although Pd(OAc)₂-catalysed alkoxylation of the C(sp³)–H bonds mediated by hypervalent iodine(iii) reagents (ArIX₂) has been developed by several prominent researchers, there is no clear mechanism yet for such crucial transformations. In this study, we shed light on this important issue with the aid of the density functional theory (DFT) calculations for alkoxylation of butyramide derivatives. We found that the previously proposed mechanism in the literature is not consistent with the experimental observations and thus cannot be operating. The calculations allowed us to discover an unprecedented mechanism composed of four main steps as follows: (i) activation of the C(sp³)–H bond, (ii) oxidative addition, (iii) reductive elimination and (iv) regeneration of the active catalyst. After completion of step (i) via the CMD mechanism, the oxidative addition commences with an X ligand transfer from the iodine(iii) reagent (ArIX₂) to Pd(ii) to form a square pyramidal complex in which an iodonium occupies the apical position. Interestingly, a simple isomerization of the resultant five-coordinate complex triggers the Pd(ii) oxidation. Accordingly, the movement of the ligand trans to the Pd–C(sp³) bond to the apical position promotes the electron transfer from Pd(ii) to iodine(iii), resulting in the reduction of iodine(iii) concomitant with the ejection of the second X ligand as a free anion. The ensuing Pd(iv) complex then undergoes the C–O reductive elimination by nucleophilic attack of the solvent (alcohol) on the sp³ carbon via an outer-sphere S_N2 mechanism assisted by the X⁻ anion. Noteworthy, starting from the five coordinate complex, the oxidative addition and reductive elimination processes occur with a very low activation barrier (ΔG^‡ 0–6 kcal mol⁻¹). The strong coordination of the alkoxylated product to the Pd(ii) centre causes the regeneration of the active catalyst, i.e. step (iv), to be considerably endergonic, leading to subsequent catalytic cycles to proceed with a much higher activation barrier than the first cycle. We also found that although, in most cases, the alkoxylation reactions proceed via a Pd(ii)–Pd(iv)–Pd(ii) catalytic cycle, the other alternative in which the oxidation state of the Pd(ii) centre remains unchanged during the catalysis could be operative, depending on the nature of the organic substrate.

This work uses DFT calculations to explore Pd(ii)-catalysed iodine(iii)-mediated alkoxylation of unactivated C(sp³)–H bonds and reveals how important the isomerization is in triggering the oxidative addition of ArIX₂ to Pd(ii).