Conditions Of Homogeneous Catalysis Research Articles

New Efficient Approach to the Preparation of (+)-Camphor and (–)-Fenchone Anils under Homogeneous Catalysis Conditions

New Efficient Approach to the Preparation of (+)-Camphor and (–)-Fenchone Anils under Homogeneous Catalysis Conditions

Oxidation of an Azo-Dye via the Photo-Fenton Process under Heterogeneous and Homogeneous Conditions

In today’s industries, a diversity of processes give rise to increasing numbers of non-biodegradable compounds that need to be degraded totally or transformed to other less toxic and/or more biodegradable compounds, before their discharge into the environment. One such compound chosen for this study is Orange II, a representative azo-dye that is widely used and easy to monitor in its degradation. The photo-Fenton process was used under heterogeneous and homogeneous conditions to study several different variables. At the end of this research, a comparative study was carried out between the two types of catalysis. It was observed that better results in primary degradation and mineralization were provided by homogeneous catalysis. The photo-Fenton process takes place effectively under heterogeneous and homogeneous catalysis conditions. The process is much faster under homogeneous conditions than under heterogeneous conditions (99.9 and 24% after 90 min, respectively, especially when only 2 ppm of iron in solution is required). Mineralization was observed through total organic carbon, through the variable C/Co as a function of time during photo-Fenton and Orange II degradation, and the data obtained for the final oxidation capacity are in agreement with the experimental percentages of mineralization. A linear fit was observed using the Chan–Chu kinetic model for heterogeneous and homogeneous catalysis. For heterogeneous catalysis, 56% mineralization was reached whereas the model predicts 63%. Regarding homogeneous catalysis, according to the model, 100% mineralization is reached because (1/σ) takes a value greater than 1 since the model calculates it on infinite time.

Local pH Modulation during Electro-Enzymatic O2 Reduction: Characterization of the Influence of Ionic Strength by In Situ Fluorescence Microscopy.

Understanding how environmental factors affect the bioelectrode efficiency and stability is of uttermost importance to develop high-performance bioelectrochemical devices. By coupling fluorescence confocal microscopy in situ to electrochemistry, this work focuses on the influence of the ionic strength on electro-enzymatic catalysis. In this context, the 4 e-/4 H+ reduction of O2 into water by the bilirubin oxidase from Myrothecium verrucaria (MvBOD) is considered as a model. The effects of salt concentration on the enzyme activity and stability were probed by enzymatic assays performed in homogeneous catalysis conditions and monitored by UV-vis absorption spectroscopy. They were also investigated in heterogeneous catalysis conditions by electrochemical measurements with MvBOD immobilized at a graphite microelectrode. We demonstrate that the catalytic activity and stability of the enzyme both in solution and in the immobilized state at the bioelectrode were conserved with an electrolyte concentration of up to 0.5 M, both in a buffered and a non-buffered electrolyte. Relying on this, we used fluorescence confocal laser scanning microscopy coupled in situ to electrochemistry to explore the local pH of the electrolyte at the vicinity of the electrode surface at various ionic strengths and for several overpotentials. 3D proton depletion profiles generated by the interfacial electro-enzymatic reaction were recorded in the presence of a pH-sensitive fluorophore. These concentration profiles were shown to contract with increasing ionic strength, thus highlighting the need for a minimal electrolyte concentration to ensure availability of charged substrates at the electrode surface during electro-enzymatic experiments.

Transformations of Carbon Dioxide under Homogeneous Catalysis Conditions (A Review)

Transformations of Carbon Dioxide under Homogeneous Catalysis Conditions (A Review)

Technological aspects of synthesis of poly(ethylene glycol) mono-1-propenyl ether monomers

Abstract For the first time, the technological aspects of the highly productive and selective synthesis of UV-reactive poly(ethylene glycol) mono-1-propenyl ether monomers was developed. The solvent-free isomerization of model commercial available 2-allyloxyethanol and allyloxypoly(ethylene glycol) derivatives, type Allyl–[OCH2CH2] n –OH, n = 1–5, into a 1-propenyl derivative under the homogeneous catalysis conditions using the ruthenium complexes were evaluated. The effect of a various reaction conditions (i.e. the concentration of [Ru] complex, the reaction temperature, reaction gas atmosphere) together with trace amounts of allyl hydroperoxides formed via autoxidation reaction of allyl substrates on the productivity of catalyst was examined in detail. Moreover, the significant role of the allyl substrate structures on the catalytic activity of ruthenium catalysts were also recognized. The optimal parameters of the scaled-up synthesis together with productivity of catalyst were first established.

Synthesis, Structural Features, and Catalytic Activity of an Iron(II) 3D Coordination Polymer Driven by an Ether-Bridged Pyridine-Dicarboxylate

New iron(II) three-dimensional coordination polymer (3D CP), [Fe(µ3-Hcpna)2]n (1), was assembled under hydrothermal conditions from 5-(4’-carboxyphenoxy)nicotinic acid (H2cpna) as a trifunctional organic N,O-building block. This stable microcrystalline CP was characterized by standard methods for coordination compounds in the solid state (infrared spectroscopy, elemental analysis, thermogravimetric analysis, powder and single-crystal X-ray diffraction). Structure and topology of 1 were examined and permitted an identification of a 3,6-connected framework of the rtl topological type. In addition, compound 1 acts as effective catalyst precursor for oxidative functionalization of alkanes (propane and cyclic C5−C8 alkanes) under homogeneous catalysis conditions, namely for the oxidation of saturated hydrocarbons with H2O2/H+ system to produce ketones and alcohols, and for alkane carboxylation with CO/H2O/S2O82− system to obtain carboxylic acids. The influence of an acid promoter and substrate scope (propane and cyclic C5−C8 alkanes) were investigated.

Development of reusable palladium catalysts supported on hydrogen titanate nanotubes for the Heck reaction

Palladium catalysts supported on hydrogen titanate nanotubes were prepared by adsorption of palladium(II) acetate from dichloromethane solutions. At low Pd(OAc)2 loadings (up to 5wt.%), the catalysts contained only highly dispersed chemisorbed Pd0 and Pd2+O species (XPS). Characteristic signals of Pd(OAc)2 were not detected in these catalysts by FT-IR, FT-Raman, of XPS, indicating decomposition of the precursor salt due to the strong metal–support interaction. An increase in the palladium loading resulted in an increase in the proportion of Pd0 species and the appearance of some supported Pd(AcO)2 (XPS). In the sample with the highest palladium loading (8.84wt.% of Pd(OAc)2), formation of small (∼1.2–2.4nm) palladium-containing clusters was detected on the support surface by HRTEM. Catalytic activity was tested in the Heck reaction between 4-bromobenzaldehyde or 4-bromostyrene and styrene. Only the E-isomers of the corresponding cross-coupled products were obtained. The activity and TON numbers of the supported Pd catalysts were higher than those of the palladium(II) acetate under homogeneous catalysis conditions. Strong palladium–support interaction resulted in the generation of catalytically active Pd(0) species without additional reduction pretreatment of the catalyst. The possibility of reuse of the same catalysts in several catalytic cycles was tested. It was found that both the Pd loading in the catalysts and the amount of water in the support have a strong influence on the catalyst’s deactivation. A catalyst with stable activity, able to be recycled at least five times, was prepared with Pd loading of 5wt.% of Pd(AcO)2 using titanate nanotubes calcined at 350°C for 2h prior to the preparation of the catalyst.

Assessing the Activity of Solid-Suported SnCl2 Catalysts on the Oleic Acid Esterification for Biodiesel Production

The search for cleaner methodologies has forcing the chemical industry to seek environmentally benign acid catalysts. SnCl2.2H2O is an affordable commercially Lewis acid, water tolerant and easy to handling, cheaper, and less corrosive. Recently, we have demonstrated that it is an efficient catalyst to produce biodiesel in homogeneous catalysis conditions. In this work, we have supported SnCl2.2H2O over different solid matrix (i.e., such as SiO2, Nb2O5 and ZrO2) and evaluated its catalytic activity in FFA esterification reactions. In this case, the reaction occurs in heterogeneous phase bringing with itself all the pertinent advantages to this rational system as the best separation of products and reuse of the catalyst. It was appraised reaction parameters such as thermal treatment temperature nature of the support; leaching test was also accomplished.

Towards a more sustainable production of triacetoneamine with heterogeneous catalysis

The acid-catalyzed condensation of acetone and ammonia to directly produce 2,2,6,6-tetramethy-4-piperidone (triacetonamine) was studied under both homogeneous and heterogeneous catalysis. The selectivity to the desired product was affected by the presence of a complex reaction network involving several kinetically parallel and consecutive reactions, leading to by-products such as diacetonealcohol, diacetoneamine, mesityl oxide, acetonine, and 2,2,4,6-tetramethyl-2,5-dihydropyridine. The latter was the most undesired by-product, since its formation was irreversible. Key elements in achieving high selectivity in the direct synthesis of triacetonamine were the molar feed ratio between acetone and ammonia, and the amount of water in the reaction medium; in fact, water was found to play an important role in the transformation of the intermediate acetonine into triacetonamine. Compared with homogeneous catalysis, the selectivity achieved by the use of the heterogeneous H-Y zeolites was controlled by means of a proper selection of the zeolite features. In fact, the use of a highly hydrophilic H-Y zeolite made it possible to achieve the same selectivity as that obtained under homogeneous catalysis conditions, with the additional advantage of using an easily separable and reusable catalyst, which showed no deactivation.

Stoichiometric and Homogeneous-Catalytic Diboration of the NN Double Bond of Azobenzene

The diboration of the N=N double bond of azobenzene was achieved by reaction of the [3]diboraplatinametalloarenophanes derived from ferrocene, [Fe(eta5-C5H4)B(NMe2)Pt(PEt3)2B(NMe2)(eta5-C5H4)], and bis(benzene)chromium, [Cr(eta6-C6H5)B(NMe2)Pt(PEt3)2B(NMe2)(eta6-C6H5)], with an excess of azobenzene in toluene at elevated temperature. The formation of the anticipated ansa-bis(boryl)hydrazines was substantiated by the determination of the molecular structure of the chromium derivative by X-ray diffraction. The synthesis of the ansa-bis(boryl)hydrazine derivative of ferrocene could also be accomplished under homogeneous catalysis conditions. Hence, reaction of the well-known [2]boraferrocenophane, [Fe(eta5-C5H4)2B2(NMe2)2], and azobenzene in the presence of 5 mol % [Pt(PEt3)3] afforded the bis-borylated hydrazine derivative in good yields.

Reactions of Polyfluorinated Telomeric Alcohols with ε-Caprolactam

The possibility of preparing fluorinated oligomeric derivatives of e-aminocaproic acid by reaction of polyfluorinated telomeric alcohols H(CF2CF2) n CH2OH (n = 1-4) with e-caprolactam under conditions of homogeneous catalysis (triethylamine, dimethylformamide) was examined. The thermal stability of the oligomers was studied in relation to the fluorine content.

Activation of cis-ReOBr 3(PPh 3) 2 by means of photoimmobilization

The possibility to activate cis-ReOBr 3(PPh 3) 2 (inactive under homogeneous catalysis conditions) by photoimmobilization on different supports is demonstrated. The systems obtained are active in the liquid-phase hydrogenation of 1-hexene and m-nitrobenzoic acid. We propose various mechanisms for grafting the complex in darkness and under UV irradiation. The samples photoimmobilized on anatase are the most active.

Synthesis of aryl- and hetarylphosphonates

The reaction of tris(trimethylsilyl) phosphite with aryl or hetaryl halides under homogeneous catalysis conditions gave bis(trimethylsilyl)phosphonates. Treatment of these products with methanol gave the corresponding arylor hetarylphosphonic acids in quantitative yield.

Preparation of arylphosphonates by the reaction of aryl halides with tris(trimethylsilyl) phosphite under homogeneous catalysis conditions

The reaction of tris(trimethylsilyl) phosphite with aryl bromides under homogeneous catalysis conditions gives bis(trimethylsilyl)arylphosphonates. The desilylation of these phosphonate products with methanol leads to arylphosphonic acids.

ChemInform Abstract: Carbon Dioxide as an Alternative C1 Synthetic Unit: Activation by Transition‐Metal Complexes

The carbon dioxide molecule has been of limited importance as a synthetic unit in organic chemistry. When it is coordinated to transition metals, however, completely new possibilities arise; CO2 can bond to metal complexes in a variety of ways and can enter into insertion and coupling reactions, or become catalytically attached to other substrates. The formation of CC bonds between carbon dioxide and unsaturated hydrocarbons under conditions of homogeneous catalysis makes available new synthetic routes to industrially interesting organic compounds.

Carbon Dioxide as an Alternative C1 Synthetic Unit: Activation by Transition‐Metal Complexes

AbstractThe carbon dioxide molecule has been of limited importance as a synthetic unit in organic chemistry. When it is coordinated to transition metals, however, completely new possibilities arise; CO2 can bond to metal complexes in a variety of ways and can enter into insertion and coupling reactions, or become catalytically attached to other substrates. The formation of CC bonds between carbon dioxide and unsaturated hydrocarbons under conditions of homogeneous catalysis makes available new synthetic routes to industrially interesting organic compounds.

Polymerization of vinylacetylene compounds under the action of palladium salt in conditions of homogeneous catalysis

The polymerization of vinylacetylene compounds under the action of palladium salts in conditions of homogeneous catalysis was studied. Based on the results of IR and UV spectroscopy, and also of diene synthesis with maleic anhydride it was shown that the vinylacetylenes are polymerized selectively at the triple bound to form trans-polyenes.

Kinetics of reaction of 2,3,5-trimethyl-1,4-hydroquinone with isophytol under conditions of homogeneous catalysis by Lewis acids

Kinetics of reaction of 2,3,5-trimethyl-1,4-hydroquinone with isophytol under conditions of homogeneous catalysis by Lewis acids